The other Dirofilaria

Most of the time, when we talk about the parasite Dirofilaria in animals, we’re talking about Dirofilaria immitis - a.k.a. heartworm. However, it’s not the only member of this parasite family that is found in dogs and cats. Another one, Dirofilaria repens, is present in pets in many regions, and it can also spread to people via mosquitoes.

A recent report from Belarus, highlighted in ProMed-Mail, describes 21 cases of dirofilariasis caused by D. repens. Interestingly, this is a relatively new finding for the area, as the disease was not reported in Belarus before the mid-1990s.

This parasite naturally infects dogs, cats, and a variety of wild carnivores like wild canids (e.g. wolves, coyotes, foxes). Mature worms live in tissues under the skin of a suitable host, where they produce larvae (microfilaria). These larvae enter the bloodstream and can then be taken up by mosquitoes that bite the host. If a mosquito feeds on an infected animal and then a person, it’s possible to transfer the larvae to the person. People aren’t natural hosts, and the parasite almost never develops into its adult state. However, as the parasite undertakes its futile migration through a person’s tissues, trying to find a place to mature, the body mounts an immune response. This results in local inflammation, typically causing the development of little tissue nodules. Very rarely, more serious infections can occur, in which case surgical excision of the nodule, with or without antiparasitic drugs, is the typical treatment.

Heartworm prevention practices should also prevent establishment of D. repens infections in dogs. Control of the parasite in the dog population is an important control measure in areas where it exists, but if the parasite is also present at high levels in wild animals, that complicates things. Basic mosquito control and avoidance measures also make sense.

Image source: http://www.cdc.gov/dpdx/dirofilariasis/index.html

What does a puppy have to do with herd health?

The new puppy, now named Merlin, is keeping things busy around here. (Note to self: avoid getting a new puppy during miserable weather.  Standing in pouring, driving rain at 4 AM is not fun. Okay, enough whining.)

Yesterday, I wrote about the new puppy's deworming plan. One thing I forgot to mention was the rest of the "herd." By that, I mean Meg, our 11-year-old Lab. Herd health gets a lot of attention in food animals and to a lesser degree in horses, but many concepts remain important for pets. Specifically, when you introduce a new member into the herd, you might change disease risks or required preventive measures for other members of the herd.

Meg lives a pretty cat-like existence. She sleeps, eats, walks far enough to go outside to pee and, well, that's about it. As an older dog who has very rare contact with other dogs, her risk of exposure to many microorganisms, such as parasites, is limited. However, since we brought a new little furry vector into the house, Meg might be exposed to some things that haven't been much of a concern in the past. Her habit of eating whatever she can find (including poop), increases that risk further. So, what's the herd health plan?

It's not too detailed, actually.

  • One thing is making sure that we deworm Meg and we don't just focus on the puppy. She might be exposed to anything the puppy is/was shedding. We're usually pretty lax on deworming her in the winter months, but she'll get a couple of doses of dewormer alongside the puppy. 
  • Poop removal. Since Meg's a notorious poop-eater, we'll want to remove Merlin's waste promptly. That's pretty straightforward. If she can't find it, she can't eat it. It's also important to make sure that old feces aren't left around, because some parasites require time in the environment to become infectious, so regular feces removal prevents accumulation of infective forms of some. The current temperature is at the lower limit of where Toxocara eggs are able to develop into infectious larvae, and the risk will probably be pretty minimal as the temperature drops over the next few days, but it's not hard to make sure the yard gets cleaned up.
  • If we find something in the puppy, then we'll have to consider whether Meg might be exposed or at risk too, and decide whether she needs to be tested or treated.

The other aspect of the herd is the non-canine component of the household (i.e. the kids). The key points for that, in terms of zoonotic parasites, are cleaning up feces from the yard, avoiding fecal contact, hand washing, treating the dogs appropriately to reduce parasite shedding and other basic feces-avoidance measures.

New arrival...

Hide the kids’ toys, tune up the carpet cleaner, get ready for some sleep deprivation… there’s a new dog in the house. Last night, the yet-to-be-named ("he who shall not be named" having been rejected by Heather) little yellow critter arrived. Meg (the existing dog) seems relatively content, or at least resigned. The cat... not so much, but he's already established who's the boss.

So, while I'm momentarily not trying to convince the puppy to pee outside, I’ll take this opportunity to hopefully practice what I preach and describe what we’re doing for things like vaccination, deworming and other infectious disease-related topics.

To start things off: What’s the deworming plan?

  • Roundworms (Toxocara canis) are the main concern in puppies. It’s generally a good idea to assume that a young puppy has roundworms, regardless of from where it came and how well cared for it was.
  • Canadian parasite treatment guidelines are to treat puppies with a drug that will kill Toxocara worms at 2, 4, 6 and 8 weeks of age, then monthly until 6 months of age. Our little guy is 9 weeks old and has already been treated a couple of times for roundworms, plus he's had one treatment for coccidia (a different parasite that was found on a recent fecal exam).  He’ll get another dose of pyrantel pamoate in the next day or two, then monthly until he’s 6 months old. (If someone gets a puppy and it hasn’t been treated like this or its vaccination history isn’t known, it is recommended to give 3 treatments 2 weeks apart, then monthly until 6 months).
  • A fecal exam will be done on the puppy in the near future. It’s not an emergency since it won’t impact what I do at the moment in terms of treatment, but it’s good to see if there are any parasites that aren’t killed by the chosen dewormer (e.g. tapeworms) and to detect resistant parasites (i.e. Toxocara eggs still found in feces after appropriate treatment).
  • No flea treatment now since he doesn’t have any evidence of a flea infestation and it’s not very likely he’ll be exposed to fleas before the spring based on the current climate where we are.
  • No heartworm treatment until the spring either. The Canadian Parasitology Expert Panel (CPEP) recommentaion is for dogs to receive monthly heartworm preventive treatments beginning at a maximum of two months of age. So, I’m not really following that one, but given the time of year, the low prevalence of heartworm in the area he's from and the fact that the puppy wouldn’t have had too much risk of mosquito exposure because of its age and indoor housing, the risk of heartworm exposure this season is very low.

More updates to come, and hopefully not too many descriptions of how to clean puppy feces off of various surfaces.

 

Identifying the "right" parasite control program

Here is another guest blog, this time from the "worm-guy" Dr. Martin Nielsen of the Gluck Equine Research Center at the University of Kentucky.

At the recent 9th International Conference on Equine Infectious Diseases (EIDC) in Lexington, Kentucky several sessions were focused on parasite control of horses. Drug resistant parasites are a world-wide problem in equine establishments, and it has become a challenge to define a simple and useful set of guidelines to be used by horse owners. As many readers of the Worms & Germs Blog will be aware, there is no longer a “one size fits all” program, and parasitologists instead often talk about the complexity related to the different parasites that often infect the horses in concert, their interactions with their hosts, and how to interpret fecal egg counts. While this is all useful and important information, it can be frustrating when it does not readily come with some practical guidance.

Equine parasitology is rarely well-represented at parasitology conferences. Usually, there are less than a handful equine abstracts, and often not even enough for a separate session. The three or so participating equine parasitologists often have to create their own little scientific session over a cup of coffee during the breaks. The EIDC was much different. It had participation from leading equine parasitologists from Sweden, Denmark, Finland, Germany, United Kingdom, Canada, Brazil, and the USA. More than 30 parasitology abstracts were presented at the meeting, and a special session critically addressed the most pressing research needs for equine parasite control. During the conference, an international equine parasitology consortium was formed, and it will serve to coordinate future research efforts and to communicate consensus-based guidelines for parasite control.

So, what are these recommendations then?  New research presented at the EIDC illustrated very well that general recommendations are more straight-forward than often anticipated. Work performed by Kurt Pfister and colleagues in Germany illustrated that fecal egg counts are useful for monitoring and controlling parasite transmission by the means of selective therapy. Two Danish studies illustrated that one or two yearly strategic treatments applied to all horses are advisable to effectively break the life cycle of large strongyles, particularly the bloodworm, Strongylus vulgaris. In other words, a basic foundation of treatments can be defined, upon which the some of the more parasitized horses can be identified to receive additional treatments with a selective approach. Several presentations underlined the need for yearly routine evaluations of the efficacy of the anthelmintic drugs used on each farm. The fecal egg count reduction test is the most important use of the fecal egg counts. [Weese comment: that's when you do a fecal egg count before and after deworming, and compare the egg counts to see how much they dropped, as an indication of how well the dewormer worked] Perhaps most encouraging was the promising new diagnostic tools presented by several groups for detection of migrating or encysted parasite larvae. These will turn very useful for identifying horses at risk of disease and in need of deworming. One of these, developed by Jacqui Matthews and her group at Moredun Research Institute in Scotland shows great promise for measuring burdens of small strongyle larvae (cyathostomins), which can pose a threat for severe parasitic disease. With these new tools in hand, we will become able to further refine our recommendations in the future.

Echinococcus in Canada

If you ask people about tapeworms, they typically think about the "ick" factor of having a  large worm in their gut, but they probably don't get too concerned. However, some types of tapeworm infection can be serious health problems in humans and animals. One of the worst is infection by the tapeworm species Echinococcus multilocularis. A couple of recent reports about E. multilocularis in Canada have received a lot of attention.

With Echinococcus, the problem isn't the worm living in the intestine. Adult worms live in the intestinal tract of only "definitive hosts," which are primarily foxes and coyotes in North America. The worms aren't necessarily a problem for these animals, but they can pass large numbers of tapeworm eggs in their stool. The parasite's normal life cycle continues when small animals (e.g. rodents like mice and voles) swallow a tapeworm egg. The parasite then develops into a cyst in the animal's body, and if/when the little critter is eaten by a fox or coyote, the cyst gets eaten too and the fox/coyote develops a new adult tapeworm in the intestinal tract.

When it comes to people (and some other domestic species), the problem is what happens when they ingest tapeworm eggs. Like in rodents, the eggs hatch and the immature parasites migrate through the intestinal wall, and can then spread to virtually any place in the body. They can then develop into large cysts that, over a long period of time, result in serious disease. Large cysts and/or cysts in critical areas (e.g. the brain) can be devastating. Treatment is difficult, prolonged and expensive, and death rates are high.

Dogs are a bit of an oddity in this cycle, since they can carry adult tapeworms (not surprising, since they are similar to foxes and coyotes) but they can also get these large tissue cysts. From public health and infection control standpoints, dogs shedding Echinococcus eggs are the main concern, but cysts are potentially devastating in the rare dog that develops one, just as they are in people.

Recent concerns revolve around two papers, one that described a dog from British Columbia with Echinococcus cysts (Jenkins et al. Emerging Infectious Diseases 2012) and a study that identified E. multilocularis eggs in feces from 23/91 (25%) urban coyotes in Alberta (Catalano et al. Emerging Infectious Diseases 2012).

What's the risk in Canada?

It's low.  Actually it's very low, and there have been only a handful of cases diagnosed even in people in North America. But with a serious disease like this, you can't ignore it. If Echinococcus is spreading in coyotes and foxes, it creates the potential for exposure of other species (including humans). The risk gets higher as coyotes and foxes get closer and closer to people and dogs, as is happening in some areas because of urban sprawl. The more coyotes that are around and the closer they are to human populations, the greater the chance that a person or dog will inadvertently ingest a tapeworm egg from coyote feces. Dog parks may be of particular concern because of the high traffic through them and the potential for them to be a big mixing site between wildlife, pets and humans.

There shouldn't be any panic because of this, as it still remains an extremely rare disease. But, it's not much consolation that it's a rare disease if you're the one with a big Echinococcus cyst in the brain. So, while the risk is low, we don't really know (yet) whether it's changing, and it's worth using some basic practices to reduce the risk. These include:

  • The standard: Don't eat poop. Pretty straightforward but easier said than done, in many respects, since fecal contamination of the environment is pretty common. Avoiding inadvertent ingestion of feces can be done through proper handling of dog and wildlife feces and attention to handwashing.
  • Controlling rodents and preventing pets from catching and eating rodents.
  • Preventing dogs from eating wildlife feces.
  • Routine tapeworm deworming should kill Echinococcus and if a dog is at particularly high risk, more regular testing and treatment for tapeworms may be indicated. Not many dogs fit into that category at the moment, though.

Image: Echinococcus multilocularis isolated from a fox in Hungary.  Unlike the very long tapeworms of the Taenia genus, which are most commonly found in dogs and cats, Echinococcus tapeworms are quite small (the bar in the picture is 0.5 mm), but the eggs shed in the feces of animals with an intestinal infection (involving mature adult worms) are virtually identical to those of Taenia spp. (click image for source).

Pet travel misinformation

Travel always carries a risk of infectious diseases. More people are paying attention to their health and going to travel clinics to find out about these risks and what preventive measures they can take. They still constitute only a minority of travelers, but it’s an improvement. There aren’t travel clinics for pets, so travelers thinking about pets and infectious diseases need to rely on sources like their regular veterinarians and government websites.

Unfortunately, that doesn’t always result in good information, as shown in a study recently published in Zoonoses and Public Health (Davidson et al 2012). For the study, the authors called veterinary clinics in eight European countries (Austria, Belgium, Finland, France, Germany, Sweden, Switzerland and the UK) and asked them about taking a dog to Norway. They also called clinics in Norway and asked about bringing a dog to the country from an unspecified location in Europe. Calling was done not as a research survey but by a person pretending to be a pet owner.

The study focused on two main pathogens, Echinococcus multilocularis (a tapeworm that is present in some parts of Europe but not others, and one that is both an animal and public health concern) and rabies. Only 9% of clinics provided accurate information about these two problems. Some clinics (58%) referred people to government sites that have good information, but unfortunately 13% of clinics referred people to websites or government agencies that provided incorrect or incomplete information. When information from websites is included, people received correct advice 62% of the time. Not bad but not great.

Among the bad advice that was given (or important information that was not given):

  • Failure to tell people about the requirement for tapeworm treatment after arrival.
  • Incorrect tapeworm treatment information.
  • No mention of rabies titre testing.
  • False information that pets traveling to Norway don’t require tapeworm treatment.

This shouldn’t be taken as indicating that veterinary clinics aren’t competent. Travel medicine certainly isn’t something I was taught in vet school. Most veterinarians (understandably) don’t spend much time reading about problems that only occur in other geographic regions, since there’s enough other new information on which they must stay current. So, they may not have answers at the tip of their tongues when asked a question. Trying to get good information by random phone calls or as an aside during a veterinary appointment might not be the best approach. However, since we have a surprisingly mobile pet population, with pets traveling with owners to many different regions, it’s an important area for veterinarians to think about, from two standpoints:

1)   Counseling people who are traveling: As was the focus here, it’s important for people to know about disease risks and regulatory requirements for places to which they travel. Specific preventive measures (e.g. vaccination, deworming) that are not needed at home may be indicated when traveling.

2)   Diagnosing disease in returning animals: It’s easy to miss travel-associated diseases, and that can lead to bad outcomes. If veterinarians don’t ask whether a pet has traveled, they won’t realize that there might be some other diseases to consider. If they don’t know about disease concerns in other regions or (perhaps more importantly) don’t have ready access to good information about disease risks in other regions (e.g. accurate websites), they might not consider important diseases even if they ask about travel history.

This study highlights a few of the current gaps in the system, involving background knowledge, client communications and variable accuracy of electronic sources. People who are traveling with pets (or acquiring pets from abroad) should have a thorough discussion with their veterinarian (not just a casual call to the veterinary clinic, during which information may come from or through lay staff) about the situation, and they need to do their own homework. It's probably best to make sure the clinic knows that there will be travel questions in advance, so mentioning it at the time of booking the appointment might help.

As the authors of this research state “An accessible, centralized, easy to use website, that is updated by a central regulating agency and applies to all countries, would allow veterinarians to refer pet owners to one site for further information regardless of which country they are travelling from and going to.”

That's the ideal situation. Given the minimal attention that governments pay to pet animals, it's probably going to have to be an government-independent, collaborative venture. We've had some discussions about this in the past and it would be great to do, but the logistics are a bit daunting. Maybe it's time to resurrect those discussions.

 

Travel, pets and infectious disease risks

An important concept when dealing with infectious diseases is consideration of the risk that an animal has been, or will be, exposed to a particular microorganism. Some diseases vary greatly geographically, and something that's very important in one region may be rare or non-existent in another. Good veterinarians are aware of disease trends in their area and make informed decisions about vaccination and anti-parasitic treatments based on what's happening in the area. They also know which diseases are common and which are rare or non-existent.

But that only works if the pets stay in their "home" area. Traveling with pets can result in exposure to various infectious diseases they wouldn't normally encounter. If a veterinarian doesn't know a pet travels, they can't make proper recommendations for preventive medicine.

Additionally, travel history can be very important when evaluating a sick animal, since there may be diseases that need to be considered in a traveling pet that wouldn't be an issue with a local pet. However, it's easy to overlook or forget about travel history. Pet owners need to tell their veterinarians about "recent" travel with their pets. What does recent mean? It's hard to say. For some diseases, exposure within the past few days is all that's important. For others, it may be weeks or months. So, if you have a sick pet and have traveled any time in the past year with it, it's good to mention that to your veterinarian. It may have nothing to do with the current illness, but it never hurts to let them know anyway. In some situations, it may be the critical piece of information needed to trigger thinking about a specific disease.

Some examples of diseases that may be travel-related (at least to dogs in most parts of Ontario):

  • Blastomycosis, a fungal disease, tends to occur predominantly in specific areas. It's not too common elsewhere, but travel to high-risk areas puts blasto on the list of possibilities in certain cases.
  • Around here, there's no indication for heartworm preventive treatment during cold winter months, but that changes if the pet goes to areas where mosquitoes hang around all year.
  • Some tickborne diseases have very specific ranges that correspond to their primary hosts and certain vector species (such as birds). In Ontario, ticks are currently quite geographically focused and many dogs have little risk of exposure. Travel to one of the tick hotbed areas changes that, and means that certain tickborne diseases need to be considered.
  • Canine influenza currently seems like a non-entity in Ontario. We're still looking for it but haven't found it. It is present in some places in the US, and at times, is a big problem. Travel to a place experiencing a canine flu outbreak would be a good indication to consider canine flu vaccination.

What to do?

  • If you travel with your pet, part of your pre-travel checklist should be an appointment with your veterinarian to go over anything that needs to be done, be it vaccination, deworming, flea control, heartworm preventive or anything else. (It's also a good time to make sure there's nothing else going on with your pet, because you don't want a pet health crisis en route.)
  • If your pet gets sick and has traveled, make sure your veterinarian knows where you went and when.
  • If you travel regularly, even if it's not long distances, it's good to discuss it with your veterinarian to see if anything is required for your pet. Even if you just go a couple of hours away to a cottage regularly during the summer, you may be exposing your pet to something different.

Kinkajou owners beware

Kinkajous are strange little mammals from the Procyonidae family - the same family to which raccoons belong. Kinkajous are native to Central and South America and are occasionally kept as pets, but they don't make great pets because they are strictly nocturnal, can be cranky when woken during the day, and can sometimes be aggressive. Regardless, there is a niche pet trade, particularly in the US.

A recent report in Morbidity and Mortality Weekly Report describes detection of Baylisascaris procyonis (the raccoon roundworm) in pet kinkajous in the US, including:

  • A 10-week-old kinkajou in Tennessee in which Baylisascaris procyonis was found during a routine fecal examination.
  • Detection of Baylisascaris eggs from soil samples under the cages of a kinkajou breeder in Florida (the breeder from which the Tennessee animal was obtained).
  • An unrelated case (11 years earlier) in which adult Baylisascaris worms were found in the intestinal tract of two adult kinkajous that died of other causes.

No human infections (i.e. cases of larval migrans) were linked to infected kinkiajous.

Baylisascaris is a parasite that's extremely common in raccoons, rare (but concerning and sometimes over-hyped) in dogs, and an extremely rare cause of disease in people. While rare in humans, it still gets a lot of attention because when disease does occur, it can cause serious neurological damage, typically in children. The damage is caused by migration of parasite larvae through the body, and through the brain. This can occur after someone swallows infective parasite eggs, which then hatch in the intestinal tract and then embark on their journey through the body.

It's unclear whether Baylisascaris is a common problem in kinkajous (like it is in raccoons) or a rare finding (like it is in dogs), since this report only describes the parasite in a small number of animals, and no larger studies of intestinal parasites in kinkajous have been reported. It would be useful to know whether kinkajous are true reservoirs of this parasite (and therefore whether we should consider all kinkajous to be carriers) or whether infection is just an unusual finding.

Overall, the public health risk is likely limited.

  • There aren't that many pet kinkajous around, as far as I know.
  • While Baylisascaris is nothing to dismiss, to get infected, a person still has to eat infective eggs from feces. The likelihood of transmission from a pet to a person is therefore low if good basic hygiene measures are used.
  • The parasite eggs are not immediately infectious. They have to sit around in the environment before they are infectious, usually for 2-4 weeks. Therefore, prompt removal of feces and careful attention to basic practices like hand hygiene should greatly reduce the risk of transmission.
  • Routine testing and deworming of pet kinkajous should reduce the risk even further.

What does this mean for pet kinkajou owners? Not a lot beyond what would normally be recommended. Pet kinkajous should have good veterinary care and regular fecal examinations. Regular deworming should be discussed with the attending veterinarian, and good hygiene practices should be used to avoid contact with feces, especially old feces.

Photo credit: Robrrb at en.wikipedia

Reducing risks with raccoon latrines

An interesting paper in the journal Emerging Infectious Diseases (Page et al. 2011) describes an impressively large effort to study the effect of anthelmintic (dewormer) baiting on parasite contamination at raccoon latrines sites in Indiana.

Raccoon latrines can be highly contaminated with various parasites, because raccoons congregate at these sites and use them as "communal toilets." Of all these parasites, the raccoon roundworm, Baylisascaris procyonis, gets the most attention.  It is very common in raccoons, but it is also a very rare cause of disease in people who swallow the infective parasite eggs from the environment.  In some of these people the parasite larvae can cause very serious neurological disease which can be very difficult to treat.

In this study, the research team identified 559 raccoon latrines in north-central Indiana. They removed debris from the areas and used a torch to help kill the parasite eggs that were there (this is one of the very few effective ways to kill the very hardy eggs of Baylisascaris). At a selection of latrine sites, they also collected baseline fecal samples. After this was all done, they distributed dewormer (pyrantel pamoate) baits in half the areas once a month (leaving the other half of the areas as controls). They then collected fecal samples at all the latrine sites approximately 6, 12 and 18 months later.

Fecal samples were tested for B. procyonis eggs. Also, they captured mice from some of the study patches. Like people, mice are intermediate hosts for B. procyonis, and they can be infected in the same manner, so researchers looked for B. procyonis larvae in the brains of the mice.

Overall, they tested 1797 fecal samples. In the first round of sampling, 33% of samples contained B. procyonis eggs. The prevalence of eggs decreases significantly (3-fold) after baiting by the first recheck, and stayed at that level throughout the study. By the one-year sample time, there was also a significant decline in B. procyonis larvae in the brains of mice (27% vs 38%).

This impressive study shows the potential impact of controlled and somewhat practical interventions on the presence of some concerning microorganisms. Certainly, no one is going to be able to treat all raccoon latrines with a torch. However, dewormer baiting might be a consideration in areas that are close to human populations, along with other control measures. Dewormer baiting could be relatively cost-effective in this case. It won't eliminate the problem, but it might help reduce environmental contamination and the associated potential for human and domestic animal exposure.

More information about Baylisascaris and raccoon latrines is available in our archives.

Infectious disease considerations for fostering pets

Humane societies and shelters are often overwhelmed by the number of animals that come in. It's pretty uncommon to see much (if any) empty space in most shelters, and overcapacity shelters lead to increased risk of disease transmission, outbreaks and suboptimal care of the animals that are there.

One way of helping deal with overcrowding is fostering animals to people's homes for periods of time. Typically, foster homes take animals when shelters are at capacity, or take specific animals such as nursing cats, which are more difficult to care for properly in a shelter.

Most places have protocols for fostering, but they're not always very comprehensive and they don't always adequately cover some important areas. If you are thinking about fostering shelter animals, you need to think about the risks and whether you can manage them.

Are there people in the household that are at increased risk of infection?

Fostered animals should be assumed to be at higher risk of carrying and transmitting various infectious diseases. They can have high rates of carriage of various intestinal bacteria and parasites, along with a host of other microorganisms (e.g. ringworm). They may also be more likely to bite and scratch, not necessarily because they are aggressive, but often because they are young animals that may do so when playing. They may also be more likely to poop in the house.

Households with children under the age of 5, elderly individuals, pregnant women or people whose immune systems are compromised are at increased risk of various infections, both in terms of the likelihood of becoming infected and the likelihood of developing more severe disease. Households with these types of individuals should not foster animals. They are much better off having their own lower-risk pets.

Are there any "resident" pets in the household?

You might expect that someone willing to foster animals would also have their own pets, but that's not always the case. Non-pet owners are actually ideal, since this negates any risk of diseases being spread from or to household pets that live there long-term. However, it's more typical that foster homes also have such resident pets.

Are there any pets in the household that are at higher risk for infection?

As with people, there are some animals that are at increased risk of infection. These include the very young, very old, pregnant and pets with compromised immune systems. The latter group would include pets with chronic illnesses, those being treated with high doses of steroids for various diseases, animals with cancer, animals with diabetes, and a range of other issues. People owning a pet that fits into one of these categories should not foster animals because of the risk to their own pet. 

How do you reduce the risks associated with fostering animals?

  • May sure there are no high risk people or pets in the household.
  • Make sure the shelter or organization knows what they are doing. Make sure they have a clear protocol that says who will be fostered and how it's done.
  • Look at the animal before you get it. Visit it at the shelter. See if it looks healthy. If you have any questions, make sure it's examined by a vet before it reaches your home.
  • Use good hygiene. Wash your hands regularly. Properly clean up feces and clean litterboxes regularly.

If you have pets of your own:

  • Make sure they are vaccinated and on an appropriate parasite control program.
  • Keep the new animal away from your pet at the start. That lets you find out more about the animal, and it gives you more time to see if there are potential infectious disease concerns.
  • Do a controlled introduction of the new animal. Slow, supervised introduction of the animals can reduce the risk of bites or scratches.

Fostering is a good way to reduce pressures on humane societies and shelters, and to provide better care for some animals, like pregnant animals or those with young kittens/puppies. A good fostering program can be set up with limited risk to all involved, but infectious disease risks can never be completely eliminated. By accepting a new animal into your house, you increase the risk of exposing yourself and anyone else (human or animal) to infectious diseases. That's just a fact of life.

(click image for source)

California Vet Association park safety tips

The California Veterinary Medical Association has published recommendations for dog park safety. The document, entitled "Dog parks harbor risks as well as fun" emphasizes the benefits of park visitation but points out some risks and recommended precautions. Some of the risks associated with park visits include bites, scratches, and exposure to various infectious diseases.

Some basic and practical precautions that are recommended include:

  • Ensure your dog's vaccination status is current.
  • Make sure your dog is socialized and behaves well around people and other animals.
  • Monitor your dog closely.
  • Avoid mixing small dogs and big dogs.
  • Bring water for your dog to drink.
  • Clean your dog's paws when you leave the park (I'm not sure that one's very useful).
  • Have your veterinarian check your dog regularly for parasites (and other infectious diseases or risk factors).
  • Talk to your veterinarian about any (other) precautions you should take.

Overall, the document provides some useful and very practical information. A few things I would add:

  • Keep your pet away from the park when it's sick.
  • Make sure you promptly pick up dog poop and dispose of it properly.
  • If it's an off-leash park, spend a few minutes watching the other dogs that are there before deciding whether to let your dog off its own leash.
  • Make sure your veterinarian knows that your dog goes to the park if it becomes sick. There are some diseases that are more likely in dogs that visit parks, and outbreaks can also be associated with parks.  Knowing that your dog has access to a dog park might be an important part of the diagnostic process. As well, knowing that you visit the park regularly might change your veterinarian's recommendations for vaccination and deworming.

(click image for source)

Baylisascaris and dogs

Recently, I was speaking with a physician who mentioned that a colleague has recommended that people with raccoons in their yard get rid of their dogs because of the risk of Baylisascaris procyonis. This parasite, also known as the raccoon roundworm, can cause severe neurological disease in people that ingest infective parasite eggs from the environment.

The most severe type of disease caused by the migrating larvae of this roundworm (neural larval migrans) is very nasty, and usually causes death or serious, severe neurological deficits.  However,  the recommendation to get rid of dogs when there are raccoons around makes no sense. Here's why:

  • The main host for Baylisascaris is the raccoon. A large percentage of healthy raccoons (over 90% in some areas) are infected and pass large numbers of parasite eggs in their stool.  Exposure to eggs from raccoon feces is the main source of human infection.
  • Human infections are very rare. They predominantly occur in people that are at increased risk of ingesting feces or dirt, based on their age or behaviour.
  • Dogs can be infected with Baylisascaris, but this is rare.
  • The small number of dogs that are shedding Baylisascaris in their feces do not pose an immediate risk to people. Eggs that are passed in feces are not immediately infective. Eggs must mature in the environment (which usually  takes 2-4 weeks) before they are able to cause infections.
  • There are no clearly documented cases of dogs being a source of human infection.
  • The main risk from dogs is probably the potential for dogs to carry old (i.e. infectious) Baylisascaris eggs into houses on their haircoats, after roaming around raccoon infested areas.

How do you reduce the already very low risk associated with Baylisascaris and dogs?

  • Discourage raccoons from living near your house. Raccoons defecate in certain areas or "latrines," where the soil becomes heavily contaminated with raccoon feces, and where tremendous numbers of infectious eggs can be present.  If you make your yard uninviting to raccoons, then they won't establish a latrine near your house.
  • Carefully clean any raccoon latrines that might be on your property.
  • Don't let you dog have contact with raccoon latrines.
  • If your dog has had contact with a raccoon latrine, give it a bath. Baylisascaris eggs are sticky and can stick to the dog's coat quite well, so a thorough bath is much better than a quick rinse or brush. Wear gloves and some form of protective outwear (e.g. a coat that you take off after and promptly launder) while bathing the dog. Wash your hands thoroughly when done.
  • Closely supervise people at increased risk of ingesting feces or dirt (e.g. young children) when they're outside.
  • A routine deworming program will eliminate Baylisascaris in the intestinal tract of a pet dog, in the unlikely event it's been infected.
  • Prophylactic treatment of dogs that have eaten (or have a tendency to eat) raccoon feces could be considered, but the need and usefulness of this is not clear.

Bottom line: You don't need to get rid of your dog if there are raccoons in your yard.  The risk of Baylisascaris infection from your dog is extremely low, and the steps above can help you decrease the risk even further.  Getting rid of the raccoons (instead of the dog) will be much more effective.

More information about Baylisascaris and neural larval migrans is available in our archives.

Deworming dogs... How often?

Deworming has become a controversial subject. There are numerous opposing views, strong opinions and conflicts of interest that drive a lot of debate on the subject. There's no argument that parasites can be bad for pets and some can pose a risk to people. There's no argument that we want to reduce parasite burdens in pets to improve pet health and decrease human risks. It's the "how" that causes all of the problems. Developing deworming strategies requires consideration of a several different things, including:

  • What parasites are in the area?
  • Are the risks the same all year round or are they seasonal?
  • What parasites pose a risk to an individual pet or what are the pet's chances of exposure? (e.g. Does the pet go outside? Is it exposed to many other animals? Are there multiple pets in the household?)
  • Are there any people in the household at particular risk for parasitic infections? (e.g. young children, people with developmental disorders that might be more likely to be exposed to pet feces?)

Everyone agrees puppies and kittens need more aggressive deworming, but there are a few different approaches to managing deworming in adult animals.

The Companion Animal Parasite Council advocates monthly deworming for a few reasons. One is that, based on the duration of activity of the drugs used, monthly treatment prevents establishment of significant parasite populations in the animal (and therefore also in the animal's environment). It also keeps the treatment user-friendly - it makes it easier for people to remember to treat their pet. Some concerns with this approach include its "one plan fits all" mentality, despite the fact that there are great differences in the risks between different regions, and even between pets in the same area. There are also concerns about such heavy use contributing to the development of parasite drug resistance (which is a problem in some other species like horses and sheep), although this doesn't seem to be a major concern... at least not yet.

Recent European guidelines take a somewhat different approach and use a philosophy more geared towards individual risks for each animal. These guidelines recommend that if regular deworming is used, animals should be treated at least 4 times a year, with no more than 3 months between each treatment. This is based on some research indicating that dropping treatment to 3-4 times per year had no effect on parasite levels. This approach is therefore more conservative (in terms of the number of treatments) and probably has less of an impact on the development of resistance, but it requires more organization and thought. If used properly, it's probably a good approach.

Yet another approach was recommended by a Canadian Parasite Expert Panel. With their approach, in low-risk households (both pets at low risk for parasite exposure and people at low risk of infection), treatment is based on fecal examination results or, if fecal testing is not performed, once or twice yearly treatment is recommended. In high risk households, fecal testing is recommended 3-4 times per year, with treatment based on results, or administration of routine preventive treatment at least 2, and preferably 3-4 times per year. The main criticism of this approach is that it's more complicated and perhaps prone to errors or missed treatments.

There's no clear answer, nor should there be. There really can't be a "one program fits all" approach that properly addresses the risks for all pets (and people) in all regions. Tailoring the deworming strategy to your pet, based on your pet's and your family's risk, is the logical approach. Regardless of the chosen approach, regular fecal testing is a good (and underused) way to assess what's going on with parasites in your pet, and to identify treatment failure or the emergence of drug resistance.

Monthly heartworm prevention has an impact on what you do as well, since typical heartworm preventives are also effective against roundworms and hookworms, the main parasites targeted by routine deworming. If you are in a region where heartworm is present, monthly treatment during the heartworm season is indicated, and the main decision that needs to be made is what to do the rest of the year (where heartworm isn't a risk year-round).

Heartworm in people

Heartworm is an important problem in dogs. It's a parasitic disease caused by Dirofilaria immitis and is spread by mosquitoes. It can cause serious, even fatal disease, and routine testing and preventive medication is an important thing for dogs in areas where D. immitis is present. Dogs (wild and domestic) are the natural host for this parasite, but other species can be accidentally infected, including people and cats. People become infected by being bitten by a mosquito that is carrying the parasite, having acquired it from an infected dog. Human infections seem to be quite uncommon and, interestingly, while this is a serious problem in dogs, it tends to be rather innocuous in people. In fact, the biggest problem with heartworm infection in people is the fact that it can be confused with other, more serious problems, leading to invasive testing.

After infecting someone, D. immitis works its way to the blood vessels in the lungs. This can result in  a small area of inflamed tissue in the area. If a chest x-ray is taken, a "coin lesion" (a small, usually 1-3 cm spot) is often present. The parasite infection usually doesn't cause any problems in people, but lung cancer and tuberculosis can look the same on x-rays. Usually, open-chest surgery ends up being performed to get a biopsy of the area because of the concerns about cancer. In heartworm cases,the biopsy identifies the problem as D. immitis, which is much better than cancer, but the risks associated with having undergone such an invasive procedure are much greater than that of the parasitic infection itself.  

Typically, treatment is not recommended in people because the infection rarely causes problems and people are "dead end" hosts, meaning they cannot pass on the infection. (Unlike in dogs, infected people don't have the parasite microfilaria in their blood, which is how the infection is passed on to  mosquitoes and other animals).

Heartworm is a rare and rather innocuous problem in humans - it's nothing to lose sleep about.

Image: A diagram of a very severe case of heartworm in a dog, in which there are so many worms in the pulmonary arteries that there is "back-up" of the parasites into the right side of the heart, which is how the parasite got its common name.

More on Giardia in healthy dogs

New research provides more information on the debate about testing and treating of healthy dogs for Giardia. Two abstracts on the subject by researchers at Colorado State University were presented at the recent American College of Veterinary Internal Medicine conference.

In the first study (Clark et al), fecal samples were collected from 220 healthy dogs. Giardia was detected in 11.4% of samples, but no dogs carried assemblages (types) known to cause disease in people.

In the second study (Lappin et al), they evaluated whether treatment of healthy dogs that were shedding Giardia would eliminated the parasite. Sixteen infected dogs were treated with either fenbendazole or nitazoxanide. Eight (50%) of the dogs had to be removed from the study because of adverse effects from treatment! Of the dogs that completed the study, Giardia was still detected in 63% of dogs 34 days after treatment, indicating that the infection wasn't eliminated or that dogs were quickly re-infected.

These studies provide more support of the notion that there is no indication to test or treat healthy dogs for Giardia. Testing makes no sense when the parasite is so common but most infected dogs are healthy, and when strains carried by infected dogs are usually of no consequence to people. Giardia is essentially a normal part of the intestinal microflora in many healthy dogs. Treatment of healthy carriers isn't indicated because it can make dogs sick and because it doesn't work very well.  Remember: above all do no harm.

The bottom line is don't bother testing healthy dogs for Giardia or treating healthy dogs in normal households.

Traveling parasite roadshow

There have been a few press articles lately about the Companion Animal Parasite Council (CAPC)'s traveling roadshow on parasitic zoonoses. Measures to increase awareness about zoonotic diseases and encourage appropriate preventive measures are needed, and traveling shows such as this have the potential to reach wide audiences. However, it's important for people to critically assess everything they are told and understand the sources. CAPC produces some excellent educational material but, to my knowledge, it is fully funded by the pharmaceutical industry. That doesn't necessarily mean that CAPC's educational efforts are suspect - people participating with their roadshow have solid credentials, but you do have to critique some of the things CAPC says.

One news article about CAPC's efforts states that "The CDC reports that about 14 percent of the total U.S. population is currently infected with Toxocara, or internal roundworms, contracted from dogs and cats." I don't think that's accurate information. I believe that this is based on seroprevalence data, meaning 14 percent of the population has antibodies against Toxocara. The presence of antibodies means that at some point in life the person's (or animal's) body was exposed to Toxocara and produced antibodies.  It does not mean that these people were ever sick and it certainly does not mean that these people are currently infected. Toxocara can cause serious infections and is a concern in some regions (although it's extremely rare in Ontario), so it warrants some attention, but we need to take a balanced and evidence-based approach.

One common theme in all of the reports that I've read lately is the statement that "The CAPC recommends that pet owners use preventive medicine year-round to control internal and external parasites for the life of their cat or dog, no matter where they live."  There's simply no evidence supporting this broad of a statement. Risks in warm southern climates are not the same as in northern areas with cold winters. Prevalence rates of different parasites vary greatly between regions. There is no evidence supporting year-round deworming of dogs and cats in all regions. Statements like this weaken the other good educational information CAPC has, particularly when you consider their funding source.

Don't disregard educational materials from CAPC or other industry-sponsored groups, just don't accept them as gospel. Critically assess the information, and don't be afraid to ask for facts, or to get information from other sources.

For more information about deworming recommendations for dogs and cats in Canada, see this previous Worms & Germs post.

Baylisascaris (raccoon roundworm) in cats

A reader posed this question, with respect to having raccoons living around the house:

"One thing that causes me concern with the raccoon roundworm is the possible danger of infection to my pets and myself through the feces left behind from the raccoons in the yard and possibly in my vegetable garden. Can I acquire the roundworm from working in the soil and/or from my root vegetables etc? My cats mingle near the raccoons, they don't bother each other, should I get my cats tested?"

Certainly, working outside (particularly in soil) leads to the potential for exposure to many disease-causing agents, including Baylisascaris, as well as dog and cat roundworms (Toxocara spp.). Eating unwashed/uncooked vegetables is also a risk. However, in the grand scheme of things, the risks to the average person (not very young or very old, functional imune system) are minimal, especially if basic hygiene measures are used, such as washing hands after working in the garden, and thoroughly washing vegetables. Raccoons tend to defecate in the same specific areas most of the time (raccoon latrines), so in general gardens probably aren't common sites for raccoon feces, although it certainly can occur. Cats are probably more likely to defecate in gardens. We shouldn't take concerns about Baylisascaris lightly, because even though disease (larval migrans) is very rare, it can be very severe.

Now, about testing cats for Baylisascaris - there's not much use, for several reasons:

1) The likelihood of a positive result is very low. The prevalence of Baylisascaris in dogs is very low. Little is known about the prevalence in cats specifically, but it is presumably very uncommon there as well.

2) It can be difficult to differentiate Baylisascaris from the feline roundworm, Toxocara cati. Unless the lab has experience with this, they may not be able to tell the difference. Therefore, you might get a misleading result.

3) What does a positive test tell you? It tells you that the cat is shedding this parasite or that is has ingested eggs that are just passing through the intestine.  The risk to people is still minimal if litterboxes are cleaned regularly. Contaminated stool is not infective until it has sat around for days to weeks, so regularly cleaning the litterbox and good handwashing can control the risk.

4) What does a negative test tell you? It tells you that the parasite was not detected on this single sample. It could have been there but not been identified. It might not be there today but could be there tomorrow (though this is still unlikely). A single negative test today does not tell you too much.

5) What would you do with the results? Probably not much. In the very unlikely chance that results were positive, it would likely be recommended to repeat testing to see if eggs are just passing through or whether the animal truly is infected with the parasite. That would determine whether treatment is needed. Otherwise, recommendations would be pretty much the same in both cases (good regular deworming program as directed by your veterinarian, proper handling of cat feces...).

The best way to prevent exposure of your cat to Baylisascaris (as well as other pathogens, predatory wildlife, vehicles, etc.) is to keep it inside.

Parasite exposure from pets

A recent study from the Netherlands investigated the prevalence of zoonotic parasites in pet feces and on pets' haircoats. The authors sampled feces and fur from dogs and cats, and looked for Toxocara (roundworms), Toxoplasma, Giardia and Cryptosporidium. All these parasites are of concern from a public health standpoint because they can be found in healthy pets and can also infect people.

Toxocara eggs were found on the haircoats of 12% of dogs and 3.4% of cats. Levels were low, ranging from 1-31 eggs per sample. An important aspect of this study was that they also assessed viability of these eggs, and found that none were viable.  Therefore, even though eggs were present, they were not relevant because they were dead. Exposure to UV light and lack of humiditiy were cited as possible reasons for the death of the eggs.

Toxocara were found in the feces of 4.4% of dogs and 4.6% of cats, which is consistent with other studies of healthy pets.

Toxoplasma was not found in the feces of any cat. (Cats are the hosts for this parasite so dogs weren't tested.)

Giardia was found in the feces of 15% of dogs and 13.6% of cats. However, when these strains were typed, the vast majority were species-specific types that do not cause disease in people. Only 2 of the 15 Giardia samples were assemblage A, a type that is transmissible from pets to people. This is very important to know because crude Giardia numbers don't tell you the whole story

Cryptosporidium was found in feces of 8.7% of dogs and 4.6% of cats. However, they were not able to type these parasites to determine if they were species that typically cause infection in humans, or whether they were Cryptosporidium felis or C. canis, which rarely cause disease in people.

The discussion section of the paper contains an interesting and relevant point about exposure to Toxocara eggs on the haircoat of pets. The authors state "Even in the worst case scenario of highly contaminated fur, e.g. with the highest Toxocara [eggs per gram] of 300 and an embryonated rate of 4% from the study of Wolfe and Wright, it is necessary to ingest more than 4 grams of hair, with 12 embryonated eggs per gram, to ingest 50 infective eggs."  Based on these data, exposure to parasites from the haircoat of pets is quite unlikely.  It might be a greater concern with stray or debilitated animals, or with puppies/kittens, who could have much greater coat contamination.

The take home message: Normal contact with healthy pets likely poses minimal risk of transmission of zoonotic parasites. That being said, regularly washing your hands is still a good idea because of the potential for exposure to other types of microorganisms (e.g. bacteria), and in rare circumstances where there may be large parasite burdens on a pet. Good deworming practices, particularly for puppies and kittens, also need to be considered.

Reference: Overgaauw et al, Veterinary Parasitology, 2009.

Canadian parasite treatment guidelines for pets

Canadian Guidelines for the Treatment of Parasites in Dogs and Cats have recently been released. These guidelines were developed by an expert panel, consisting of six Canadian veterinary parasitologists and two private practitioners. They provide a good, balanced approach to the treatment of parasites, with an emphasis on the risks present in different regions and in different types of pets. There is very little objective information on which to base some of the recommendations, so many aspects are instead based on expert opinion, not necessarily hard facts, but when data are lacking, that's when opinions from independent experts are most needed. The guidelines provide an overview of recommended treatments along with an explanation of the reasoning.  This document is a useful resource for pet owners and veterinarians alike. There is also discussion about why guidelines in Canada differ from those in the US. To download these guidelines click here.

Note: Development of the guidelines was supported by a pharmaceutical company, but the information they contain was developed by the independent experts mentioned above.

Dog park closed because of bleach contamination

A dog park was closed because of an attempt by a dog-owner to disinfect puddles.  The woman was seen pouring a gallon of bleach into a mud puddle, sparking an investigation. The site was closed while city staff pumped out puddles. The woman told the person that witnessed and reported the incident that her dog had contracted the intestinal parasite Giardia in the park, and she was trying to sanitize the water.  However, authorities believe it may in fact have been a malicious act (i.e. an attempt to poison the dogs using the park).

  • Firstly, there's no way the woman could know that the park (let alone a specific puddle) was the source of her dog's infection. Giardia can be found in the environment and in the stool of a small  percentage of healthy dogs (~7% in many studies).
  • Secondly, pouring a toxic substance into the puddles in the park is obviously not an appropriate response. Bleach is a good disinfectant when it's used right, but disinfecting outdoor surfaces like this is essentially impossible. Organic debris (e.g. mud) will readily inactivate bleach, but the bleach could still make an animal sick if too much (too high a concentration) is swallowed, because it's very caustic.
  • Thirdly, for this woman to take matters into her own hands like this without consulting  someone who knows something about infectious diseases, and potentially exposing a lot of animals to high levels of bleach is irresponsible. If there was concern about the park as a source of infection, the appropriate response would have been to talk to city staff.

In reality, the risk to other dogs was probably pretty low. It’s pretty obvious when there's a lot of bleach somewhere (even just based on the smell), and in general dogs would probably be very reluctant to drink bleach-contaminated water.

One officer stated that he suspects the Giardia story was an excuse contrived by the woman when confronted by the passer-by who witnessed the bleaching incident. That’s certainly possible, but I’m surprised someone would come up with a specific excuse like Giardia.  If the woman is found, that should be easy to figure out - the diagnosis would have to be in her dog's medical record.  Police stated that the woman, if identified by the authorities, could potentially face animal cruelty charges. I think that’s pretty unlikely, considering what usually has to happen for someone to actually be charged and convicted of animal cruelty. I suspect this really was an overzealous response by someone who lacks common sense. There was no comment about whether the woman would be billed for the city staff time required to deal with the clean up - that might be a more effective deterrent to similar incidents in the future!

Parks are inherently a high-risk environment for exposure to infectious diseases. Whenever you mix large numbers of animals, especially in an area where they often pass stool, there is an increased risk of disease transmission. You have to accept that when going to a park. People should also ensure that they never take a sick animal to a park, promptly clean up stool, and may sure that their pet is on an appropriate vaccination and deworming program. Disinfection of a park will never be part of the infection control program.

More information about Giardia can be found on the Worms&Germs Resources page.

Lungworms in dogs: Parasite risk or marketing ploy?

I read a press release today entitled "New Parasite Infection Killing Pet Dogs in Southern England". It's about the lungworm Angiostrongylus vasorum. The main reservoir for this parasite in England is the common red fox. Slugs and snails are involved in transmission of the worm as well.  Infection of dogs most likely occurs through ingestion of the parasite from contaminated water or other environmental sources. The press release mentions a study that was released last year which reported an increase in the parasite in wild foxes. It mentions (without providing any data) that infections are occurring regularly dogs in some regions. This may well be true but brings to mind an important point I mentioned the other day (among others): know the source of information you are reading. I know I'm being a bit cynical, and it's possible that they have the well being of pets in mind, but the press release is from an online veterinary pharmacy, a company that obviously benefits from increased treatment of pets with dewormers.

This is made clear by their statement "Luckily there are a number of medicines available that can provide real and lasting protection from this nasty parasite. At www.vetscriptions.co.uk we recommend that all dog owners make it their business to find out about this disease and make sure that their dogs are fully protected."

Is lungworm a real and increasing threat in the UK? It's certainly possible. I don't dismiss the possibility at all.

Would I get concerned about it at this point? No. I'd look for objective information and ask my vet if there are any concerns in my particular area. Like the press release says, people should "make it their business to find out about this disease."

So what does this tell me? It reminds me that there are a lot of potential infectious disease threats out there that I need to pay attention to, but there are also a lot of people trying to make money at the same time. It could be that this company is being benevolent and honestly trying to make sure that pet owners are aware of the risks of lungworm. It's also possible they are taking advantage of a marginally relevant problem. Information like this is good for raising some questions, but getting advice from a non-biased source is critical.

Deworming kittens and puppies

Deworming adult cats and dogs is a rather controversial area at the moment. Balancing concerns about animal health, zoonotic disease transmission, drug resistance, compliance and cost is difficult. Risks vary between different regions/climates and there are no clear answers. One area that is much less controversial is deworming of kittens and puppies (less than 6 months of age), as there is general consensus that aggressive deworming is needed in these animals.This is because young animals are much more likely to harbour parasites. They are also more likely to contaminate the household environment during the litter/house training process and tend to have very close contact with people. The greatest concern tends to be about roundworms, since they are very common in dogs and cats (especially young ones) and zoonotic infections  can occur (i.e. visceral and ocular larval migrans, similar to that caused by the raccoon roundworm, Baylisascaris procyonis).

Standard deworming guidelines are:

  • Puppies should be dewormed at 2, 4, 6 and 8 weeks of age, then monthly until 6 months.
  • Kittens should be dewormed at 3, 5, 7 and 9 weeks of age, then monthly until 6 months.

Further treatments depend on various factors, including the animal's lifestyle (risk of exposure), how common different parasites are in the region and perhaps whether there are high-risk people in the household. Your veterinarian can provide the best advice for your individual pet.

Another thing to remember is that not all parasites are killed by all dewormers. Specific deworming programs need to be set up to address different parasite risks.

More information about roundworms (and other parasites) in dogs and cats can be found on the website of the Companion Animal Parasite Council, an industry-funded organization.

Photo: A large mass of roundworms from the intestine of a heavily infected animal.

More about Echinococcus tapeworms in dogs

Echinococcus granulosus is a tapeworm of dogs that causes a condition known as hydatid disease or hydatidosis in humans.  The parasite is found in many parts of the world, and is very common in some regions of southern South America, the Mediterranean, the Middle East, southwestern Asia, northern Africa and Australia.  To the best of our knowledge, E. granulosus does not occur in southern Ontario, but it is present in other parts of Canada including the western provinces and northern Ontario.  A related, but much nastier, tapeworm called Echinococcus multilocularis is much less commonly found in North America.

A previous Worms & Germs post described what is known as the sylvatic cycle of Echinococcus granulosus, which is thought to be a common route of infection for dogs in Canada.  In the sylvatic cycle, dogs become infected with Echinococcus by eating the internal organs (usually lungs and liver) of wild game such as moose and caribou.  The dogs then pass tapeworm eggs in their stool, which can cause infection in other wild animals (thus continuing the cycle) or in people who accidentally swallow the eggs.  In humans, Echinococcus forms slow-growing cysts (called hydatid cysts) in different organs of the body which can be very difficult to remove or treat in some cases.

Echinococcus also has a pastoral or domestic cycle.  In this cycle, dogs acquire the parasite by eating the internal organs of infected sheep, and sometimes other livestock such as cattle and swine.  This cycle is potentially very important in areas where there is a lot of sheep farming.  In some areas of Latin America, 20-95% of sheep at slaughter may have evidence of hydatid cysts in their organs.

It is much more difficult to tell when a dog is infected with Echinococcus compared to other tapeworms such as Taenia or Dipylidium.  An adult Echinococcus is tiny - only a few milimetres long (see picture right), very unlike the long, stringy white tapeworms that most people picture.  Dogs can carry hundreds, even thousands of these tiny tapeworms without showing any signs of illness at all.  The eggs can sometimes be difficult to detect on fecal examinations, and when they are seen they cannot be differentiated from Taenia eggs.  Nonetheless, this is still the best way to detect infection, so fecal examinations should be performed regularly.

Remember:

  • In areas where Echinococcus is known to exist, it's important to have your veterinarian perform fecal examinations on your dog's stool more frequently than the usual once-a-year, because of the serious zoonotic potential of this parasite.
  • Always wash your hands well after handling dog stools.
  • Do not let your dog eat uncooked meat, or the organs from farm animals or wild game.

For more information on Echinococcus, see Worms & Germs post entitled Echinococcus and hydatid disease - not your average tapeworm.  There is also information available on the Michigan State Department of Natural Resources site.

Lower photo credit: Ontario Veterinary College

Updated: Raccoon Roundworms - Baylisascaris procyonis

This post has been updated with new information as of October 2, 2008.

Raccoons, just like dogs and cats, can have roundworms in their intestine. Dogs are typically infected by the species Toxocara canis, and cats are infected by Toxocara cati. Raccoons are infected by a type of roundworm from a different genus, called Baylisascaris procyonis. There is one thing that all three of the parasites have in common – the larvae of these worms can infect humans, causing a condition called visceral larval migrans.

Dogs and cats are usually dewormed as puppies and kittens, and often as adults as well, which dramatically decreases the number of pets that are infected with roundworms. Raccoons are not so lucky – in the northern and northeastern parts of North America, over 70% of raccoons may be infected with Baylisascaris.  In Ontario, it has been estimated that only about 20-30% of raccoons are infected, but usually with high numbers of worms. In either case, younger raccoons are even more likely to be infected.  Infected animals may shed millions of parasite eggs in their stool, and the eggs can survive in the soil for months or even years.

After a few weeks, the eggs in the raccoon stool become infective. If a person swallows the eggs, they hatch in the small intestine and release larvae. These larvae can then burrow through the wall of the intestine and migrate through tissues all over the body, causing tissue damage and inflammation. The signs of illness are often not very specific, and may include things like fever, fatigue and nausea. If the larvae migrate through the brain or spinal cord, a person may develop neurological signs like loss of coordination and muscle control. This is called neural larval migrans, which is the most serious type of disease caused by these larvae.  If the larvae migrate through the eye, they can cause blindness.  This condition is known as ocular larval migrans.

There have been less than 25 cases of confirmed visceral larval migrans due to Baylisascaris in the USA as of 2003, but the condition is very hard to diagnose with certainty, and it is possible that many cases are mistaken for other illnesses. The disease is also very difficult to treat, and neurological damage from neural larval migrans is usually permanent, so the best thing to do is prevent infection in the first place. Here are some tips on avoiding Baylisascaris:

  • Avoid contact with raccoons. Many people think raccoons are cute, but they are wild animals. Raccoons are also a risk for transmission of rabies if a person is scratched or bitten. NEVER keep a raccoon as a pet.
  • Discourage raccoons from hanging around your house. Clear brush and seal access to basements and attics where raccoons may try to nest or form latrines. Keep garbage in tightly-closed garbage cans. Eliminate outdoor water sources.
  • Always wash your hands well with soap and water after working with soil (e.g. in the garden).
  • Clean up raccoon latrines.  This must be done very carefully - avoid getting any raccoon stool on your hands or clothes. The stool should be burned, buried or sent to a landfill. Clean the area where the stool was found with boiling water. Wash your hands very carefully when you’re done.  Follow this link for more detailed information on how to identify and clean up raccoon latrines.

Baylisascaris procyonis less commonly infects animal species other than raccoons, including skunks, and it has even been found in dogs.  It's important to have your dog's stool examined for parasite eggs on a regular basis (typically once or twice a year) and to follow your veterinarian's recommendations for deworming your dog.

More information about Baylisascaris is available on the CDC’s Baylisascaris Infection website.

Echinococcus and hydatid disease - not your average tapeworm

A previous Worms & Germs post talked about the (very low) zoonotic risk of the tapeworm most commonly found in dogs and cats, Dipylidium caninum. Dogs can also carry other species of tapeworm, such as Taenia pisiformis, which cannot be naturally transmitted to people. But dogs can also carry tapeworms from the genus Echinococcus, the most common of which is E. granulosus. Echinococcus multilocularis is much less common in North America, and can also be carried by cats.

In Canada, dogs tend to be exposed to E. granulosus when they eat certain animals, particularly wild herbivores like moose and caribou. In other parts of the world, eating sheep organs is the most common way dogs are exposed.  The immature form of the worm is found in the animal’s lungs, liver and other tissues. After being eaten by the dog, the worm matures in the intestine, and tapeworm eggs can soon be found in the dog’s stool. Tapeworm segments, as seen with Dipylidium infection, are usually not seen in the stool with Echinococcus. Under a microscope, it is possible to tell Dipylidium eggs from Echinococcus eggs, but it is not possible to tell Echinococcus eggs from Taenia eggs.

If a moose, caribou, sheep or another suitable “intermediate host” swallows the eggs from the dog stool, the parasite migrates through the animal’s body and forms cysts in various tissues which contain the immature form of the worm. If the animal dies or is killed, and a dog (or a wolf or coyote or related species) eats the cysts, the cycle begins again.

Unfortunately, humans can also be an “intermediate host” for these tapeworms. If a person ingests Echinococcus eggs from dog stool, the parasite can form cysts (called hydatid cysts) in many tissues and organs, including the liver, lungs, brain and heart. If the cysts are small and there are only a few, they may not cause any problems for years, and the person may never know they’re there. But as the cysts grow, they can get very large and start to interfere with the function of organs, or their size alone may be a problem, depending on where they are located. Treatment can be difficult – drugs are frequently not effective, and large problematic cysts may need to be surgically removed, if the surgery can be done safely. If a cyst bursts it can cause anaphylactic shock, which is very dangerous.

In Canada, Echinococcus infection and hydatid disease are most common in the western provinces. Nonetheless, everyone can take a few simple steps to help prevent exposure of people to Echinococcus:

  • Always wash your hands after handling dog stool, even if you use a plastic bag or a scoop to pick it up.
  • Your dog should have a fecal examination for intestinal parasites at least once per year, or more frequently if your dog is at increased risk of exposure to Echinococcus. If tapeworm eggs are identified, your veterinarian can prescribe medication to treat the infection.
    • Monthly heartworm preventatives that are effective against other intestinal worms are not effective against tapeworms!
  • Do not let your dog eat uncooked meat, especially the organs of sheep or wild game such as moose and caribou.

More information on Echinococcus and hydatid disease is available on the CDC’s Echinococcosis webpage.

Tapeworms in dogs and cats

Finding a tapeworm in a pet's stool can be a concerning event for some people. Tapeworms are  intestinal parasites that can be found in varying percentages of dogs and cats. A common tapeworm (at least in North America) in dogs and cats is called Dipylidium caninum, and it can be found in a high proportion of dogs and cats in some regions, particularly animals that go outside and are infested with fleas. There is minimal concern about transmission of this tapeworm to people. Taenia pisiformis (dogs) and Taenia taeniaeformis (cats) are also common, and neither of these can infect people.

People typically realize their pet has tapeworms when they see small tapeworm segments in the animal's stool. These whitish, rice-sized pieces (called proglottids, see the picture on the right) are parts of the adult tapeworm, which break off and are passed in the stool.

Tapeworms are not usually harmful to dogs and cats, particularly if only one or a few worms are present. In some situations, weight loss can occur. Affected animals may 'scoot' (drag their rear end across the ground) because of irritation from tapeworm segments that are passed in the stool.
Diagnosis of a tapeworm infestation is easiest through identification of tapeworm segments in stool. Identification of tapeworm eggs in stool samples through routine testing used for other intestinal parasites is less useful, as the bare eggs are infrequently shed in stool.  Therefore, a negative fecal egg examination does not rule out tapeworms.

Dipylidium infections are extremely rare in people. Children are at greatest risk. Disease in people, if present, is usually mild and easily treated. However, finding tapeworms in a person's stool can be distressing to the individual (and their family). Dipylidium cannot be transmitted directly from animals to people. People and pets get infected by ingesting a flea that is infected with tapeworm larvae. Therefore, flea control is the most important aspect of tapeworm prevention. People that find tapeworm segments in their stool should contact their physician to determine whether they are actually tapeworms (people often mistake other things for tapeworm segments) and to determine whether any treatment is needed.

There are specific dewormers that can be prescribed by your veterinarian to eliminate tapeworms in pets. It is also important to take measures to control fleas and prevent dogs and cats from catching and eating animals that might be carrying fleas.

Stray kittens

While visiting my parents this weekend, we came across a litter of stray kittens in the backyard. This is not an uncommon event and many people obtain their cats this way. Adopting stray kittens can be a great way to get a cat because it provides  a good home for kittens that would otherwise end up increasing the feral cat population. However, there are some things to consider to reduce the risks to your family and your other pets.

Various bacteria that can cause diarrhea in people can be carried by kittens, including Salmonella and Campylobacter. These are shed in the stool of infected animals, and people can become ill from handling the animal or stool-contaminated areas. Kittens may have higher rates of carriage of these bacteria than adult cats. Another bacterium that can be carried commonly by kittens is Bartonella henselae, the cause of cat scratch disease. This is transmitted by bites, scratches and fleas, and is just one reason for proper flea control.

Stray kittens are also more likely to carry Toxoplasma, a parasite that is a concern in pregnant women and immunocompromised individuals. Other intestinal parasites such a roundworms are also a concern. Kittens are more likely to have these parasites than adult cats.  Stool contamination of the haircoat is presumably more common in kittens as well because they are not as good about cleaning themselves as adult cats.  So just handling a kitten, even if you avoid its stool, may result in exposure to some of these parasites and bacteria.

Rabies is always a concern, and widespread exposure of people to rabies has occurred from infected litters of kittens.  While uncommon, rabies is a major concern because it is almost invariably fatal. Any stray (or recently rescued) animal that starts acting strangely should be considered a rabies-suspect and be taken to a vet immediately. [More information on rabies, and other topics, is available in our Resources page].

Stray kittens can also carry various infectious diseases that can be transmitted to other cats in the household, such as feline leukemia virus, panleukopenia, rhinotracheitis and calicivirus.

Overall, the risks from adopting stray kittens are low, but they are real. If you are going to adopt/rescue a stray kitten, keep these things in mind:
  • Take the kitten to your vet as soon as possible to identify any health issues and determine the required vaccination, deworming and flea control program
  • Wash your hands after handling the new kitten
  • Keep the new kitten in a confined area while litterbox training is underway to reduce accidents throughout the house
  • If you have another cat, make sure it is up-to-date on vaccinations before the kitten comes into the house.
  • If the kitten gets sick, make sure it is taken to a vet. If it dies suddenly, make sure you take it to your vet to determine whether testing for rabies is required.
  • Pregnant women and households with immunocompromised individuals should not adopt stray kittens.