Some Beach, Somewhere
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"Some Beach, Somewhere" is not only a popular country music song AND the name of one of the best Standardbred racehorses in the world (originally Canadian, no less!), it's also the prime source of infection for a disease called cutaneous larval migrans.
Cutaneous larval migrans is a skin disease caused by migration of hookworm larvae. The most common hookworm species involved is Ancylostoma braziliense, which can be shed in the stool and dogs and cats. Ancylostoma caninum and A. tubaeforme are other species of hookworms that parasitize dogs and cats, respectively, and can also cause the disease, but much more rarely.
Animals infected by the hookworms shed hookworm eggs in their stool. These eggs then develop into larvae, and people become infected through skin contact with hookworm larvae in the environment, particularly in sandy areas like beaches where infected animals may have defecated.
Cutaneous larval migrans is characterized by a "serpiginous (snake-like) rash" that is intensely itchy (see picture left). This is caused by the parasite larva burrowing through the skin. In North America, the disease is most common in the southeastern US and the Caribbean. Most , if not all, cases in people in Canada are associated with travel, especially to Caribbean countries; they presumably caused by exposure to hookworm larvae on the beach. Ancylostoma braziliense is not found in Canada.
The best means of controlling cutaneous larval migrans are to promptly remove dog and cat stool from the environment and dispose of it in the garbage, and to regularly deworm dogs and cats. This is important in areas where A. braziliense is endemic, but is easier said that done in areas where feral (wild) dogs are common.
Photo source: http://www.leeds.ac.uk
Sharing E. coli with your dog
A recent study, published in the American Journal of Veterinary Research, investigated the relationship of E. coli bacteria in people and their pets. This study reported a number of interesting findings:
- When they compared the molecular fingerprints of E. coli from people and pets, they were the same 10% of the time. This means that E. coli is likely often spread between people and pets in households, although there is no way to know in which direction this occurs. It's also possible, though less likely, that people are pets don't transmit E. coli to each other, but rather that they get it from the same source.
- Antibiotic resistance was common, especially in strains from people.
- They did not detect an association between bonding behaviors (e.g. sharing the bed, allowing licks on the face) and sharing E. coli. There was, however, an association between having antibiotic resistant E. coli and owners that did not wash their hands after petting their dogs or before cooking meals.
Care should be taken with the study's conclusion that close contacts like licking aren't a risk for transmitting germs. They only looked at E. coli, which is but one of many organisms that can be passed between animals and people. Licking of the face, particularly around the ears in children, has been associated with a risk of infection from the multitude of bacteria that are present in the dog's mouth.
Nonetheless, this study has some good information. My key take-home points are:
- We routinely "share" bacteria with our close contacts, including our pets. I've been saying this for a while, and this is another piece of evidence showing how closely we interact (physically, emotionally and microbiologically) with our animal companions.
- Handwashing is an important and effective infection control tool.
- We shouldn't fear our pets in terms of infectious diseases. There are always risks but for the average person with the average pet, these are very low, particularly is good hygiene practices are used.
- There are either some dedicated pet owners in Kansas or Dr. Stenske is a very good negotiator. Getting people to provide stool samples for research studies is usually very difficult! (They'll give us all the dog poop we want, but getting their own is a completely different story!)
In a University press release, Dr. Stenske sums it up nicely: "We have a lot to learn," Stenske said. "In the meantime, we should continue to own and love our pets because they provide a source of companionship. We also need to make sure we are washing our hands often."
How long do animals carry MRSP/MRSI?
I've had this question a lot lately. Methicillin-resistant Staphylococcus pseudintermedius (MRSP), which is sometimes misidentified as methicillin-resistant S. intermedius (MRSI), is an important and increasing cause of infections in dogs and cats. After an animal has had an MRSP/MRSI infection, a question people often ask is how long they will carry the bacterium?
MRSP can be carried in the nose, intestinal tract or on the skin of a small percentage of normal animals. The implications of this are not clear, but it is reasonable to assume that carriers are more likely to develop infections in certain situations (e.g. if they sustain a wound or need to have surgery), and can transmit it to other animals (and possibly people, but that's much less of a concern with MRSP than with MRSA).
Back to the question... To be perfectly honest, we really don't know. However, I think it's reasonable to assume that some animals could carry MRSP for a long period of time - certainly weeks or months, maybe even years. Staphylococcu pseudintermedius is a common bacterium in healthy dogs and cats, and has basically evolved to survive on these animals. The methicillin-resistant versions are likely no different in this respect, so it's reasonable to assume that some animals could be long-term carriers. This makes controlling MRSP more difficult. In contrast, MRSA appears to be only transiently carried by dogs and cats, probably because it is better adapted to living on humans than pets.
What you should do in the meantime if your pet has MRSP:
- Treat any infection as per your vet's instructions.
- Always complete the full treatment course.
- Wash your hands after contact with your pet, healthy or not.
More information about different types of staph bacteria can be found in the previous Worms&Germs post entitled Methicillin-Resistant Staph - What's In A Name?
Dealing with pet bites
A recent article in Canadian Living talked about how to treat pet bites. Three main tips were provided. My comments follow in bold.
1) If the bite has punctured the skin, wash the wound thoroughly with hot water, then cover with a sterile bandage. Excellent advice. Immediate cleaning of the wound is very important.
2) If the wound/scratch appears to be swelling, soak the area in a warm bath of Epsom salts: If the wound appears to be swelling (a sign of potential infection) get thee to a physician. Actually, you should "get thee to a physician" before it gets to that point. A physician should be consulted promptly following any bite over the hand, over a joint or tendon sheath (such as on the wrist or ankle), over any kind of implant or prosthesis, or in the groin area, or any bite to person who has a weakened immune system, who has had their spleen removed, or who has any serious underlying chronic disease. A large percentage of bites occur over these high risk sites, particularly the hands.
3) If the wound continues to look inflamed, visit your doctor right away.You're better off getting this addressed proactively, before the site is swollen and persistently inflamed. It's much easier to prevent bite infections than treat them.
Another tip I'd add is make sure the animal's rabies vaccination status is known and report the bite to the appropriate Public Health authorities. There's a big difference in terms of consequences and what needs to be done if it's your pet versus some random animal you know nothing about.
The best information in this article was a very important point. "What is Dr. Conway's best advice when dealing with aggressive pets? Avoid a bite altogether by taking proper precautions." That's the key. Knowing how to interact with animals is a critical aspect of bite avoidance.
More information about bites can be found in our Bite Archives and on the Worms & Germs Resources page.
Peanut butter recall now affects pet products
I'm sure you've heard about the large outbreak of salmonellosis in people in the US associated (again!) with contaminated peanut butter. Based on the extent of the outbreak, it probably should not come as a surprise that pet treats are now caught up in the recall. The FDA has announced that the recall now includes some pet food products that contain peanut paste produced by the Peanut Corporation of America (PCA) at its Blakely, Georgia processing plant. The concerns here are two-fold: the risk of disease in pets fed the treats, and risk to people handling the treats. If you have peanut butter-containing pet treats, you should stop feeding them to your pet(s) until you can determine whether or not they are affected by the recall.
The recommendation in the recall notice really applies at all times: "It is important for people to wash their hands--and make sure children wash their hands--before and, especially, after feeding treats to pets."
More information on Salmonella and pets can be found on the Womrs&Germs Resources page.
Salmonella and turtles info sheet
BarfBlog is a food safety blog run by Dr. Doug Powell, who used to be at the University of Guelph, before moving to Kansas State. (I played hockey with him and can confidently state that he is one of the better hockey goalies working in food safety in Kansas). Doug and his group have put together numerous useful, and often entertaining, fact sheets about food safety issues, as well as some related infectious disease and infection control topics. One of those is about Salmonella in pet turtles, something we've discussed on Worms&Germs periodically. The info sheet, and associated commentary from Ben Chapman, can be found here.
Sleeping sickness - Don't doze off
Particularly when the mercury is well below zero (like it has been recently here in Ontario), many people dream of warmer places, and some of the luckier ones even get to jet off to regions closer to the equator to thaw out for a while. Before you set off for a tropical destination, it's always good to do a little research so you know what you're getting yourself into, which includes being familiar with local endemic diseases.
For today's example, take African trypanosomiasis, also known as sleeping sickness. This disease is caused by a protozoal parasite called Trypanosoma brucei, which is transmitted by the bite of tsetse flies. The disease only occurs on the African continent, but it is endemic in 36 countries and poses a risk to approximately 50 million people. There are actually two subspecies of T. brucei that cause disease in man. Trypanosoma brucei gambiense tends to cause more chronic disease and has caused massive epidemics of sleeping sickness in the past. Trypanosoma brucei rhodesiense causes more acute disease, tends to occur sporadically and is more common in tourists and travellers in Eastern and Southern Africa. What a lot of people don't realize is that T. brucei rhodesiense is actually a zoonosis - the main reservoir of the organism is livestock, whereas the main reservoir of the gambiense subspecies is infected people.
The World Health Organization (WHO) places human African trypanosomiasis (HAT) on its list of seven neglected endemic zoonoses. Some of the other disease on this list have also been discussed on the Worms&Germs blog, including rabies (one of our favorites), brucellosis and echinococcosis. In the early 1960s, efforts to control HAT brought the prevalence of the disease down to less than 1 case/10 000 people. Unfortunately, for a lot of reasons, the control efforts could not be sustained, and the African continent is now facing its third major epidemic of sleeping sickness. Better and ongoing surveillance, treatment of infected animal reservoirs, and control of the vector tsetse flies are all important components of the WHO's control strategy for HAT on the African continent.
Dogs can be infected by both T. brucei gambiense and T. brucei rhodesiense, but they are not considered significant reservoirs of disease. Dogs may be more important as sentinels for human disease in endemic areas. There are, however, other Trypanosoma species that occur in dogs and people in North and South America, including T. cruzi, which causes American trypanosomiasis or Chagas' disease.
More information about zoonotic sleeping sickness is available on the WHO website, and more information about Chagas' disease in people is available on the CDC website. Keep watching the Worms&Germs blog for more posts about trypanosomiasis in pets.
Smuggling Psittacosis
As an illustration of some of the points made in the recent Worms&Germs post on animal smuggling, an outbreak of psittacosis was recently reported in Russia, which has been linked to illegally imported decorative birds. Since December 30, 21 cases of psittacosis have been reported in the Petuhovsky district of the Kurgan region. The source of the infections was reportedly a large group of illegally imported parrots and canaries. In late 2008, another group of 15 cases were reported in the Orenburg region of Russia, which were also associated with a large group of 1500 smuggled birds. Compare this to statistics from the CDC, to which only 125 cases of psittacosis were reported from 2000 through 2006.
This report reiterates the infectious disease risks than can be associated with illegally imported animals, as well as some of the welfare issues (a second article reported that some of the birds in the illegal shipment were found dead when they reached the border). It's also important to be aware of zoonotic pathogens that can be carried by even healthy pet birds.
Psittacosis, also known as ornithosis or "parrot fever," is caused by the bacterium Chlamydophila psittaci, which is commonly carried by psittacine (pronounced "sit-a-seen") birds, often without making them sick. These birds may shed large numbers of C. psittaci in their feces. When the feces dry they become dusty, which can result in people inhaling the bacteria as they work around the birds. This is the most common way for people to become infected, and can result in pneumonia. The infection can be treated with antibiotics if it is caught in reasonable time, but it can be very serious in some cases. The bacterium can make birds sick as well in come cases, in which case the disease is called avian chlamydiosis.
More information on psittacosis is available in the National Association of State Public Health Veterinarians' Psittacosis Compendium and in the Worms & Germs archives.
Mumps - from people to dogs?
Mumps is a common (and highly infectious) viral disease in people, particularly children. Typically it causes flu-like symptoms (fever, headache, aches and sore muscles) as well as painful swelling of the parotid salivary glands. These glands are located within the cheeks near the angle of the jaw, just below the ear. Illness usually lasts for about ten days, but in young adults the infection can cause serious complications, including meningitis and deafness. Because the disease is so infectious, it is recommended that anyone with the mumps be isolated for nine days - that means no going to work, school, the store or anywhere else!
Dogs may actually be able to get mumps too, but it's very uncommon. Dogs living with recently affected children have been reported to develop similar signs of illness to humans, including fever, not wanting to eat and swollen parotid salivary glands, and antibodies to mumps virus have been found in some dogs. It's also been shown that the virus grows well in canine cell cultures in the laboratory. However, there are no experimental trials that have definitively demonstrated transmission of mumps to dogs.
Because mumps is caused by a virus, antibiotics are not useful for treating the infection. In dogs suspected of being infected, specific treatment is usually not needed - just some TLC and most dogs recover within 5-10 days. There are no reports of people getting mumps from a dog - this is primarily a disease of humans.
People, but not dogs, can be vaccinated for mumps. The vaccine is part of the MMR (measeles, mumps and rubella) vaccine, which many people receive when they are children. For more information about this disease and vaccination, see the website of the Ontario Ministry of Health and Long-Term Care.
Tuberculosis in a dog in Ontario
A report in the latest newsletter from the University of Guelph Animal Health Laboratory describes a case of tuberculosis (TB) in a pet dog. The dog was a seven-year-old Bichon Frise that had an abdominal mass, low-grade fever, nasal discharge and pneumonia. Tuberculosis was diagnosed by testing a sample of the mass that was obtained during an exploratory surgery. The dog was euthanized because of the poor prognosis and because of concerns about transmission to people in the household.
Tuberculosis has historically been one of the most important infectious diseases in people and has re-emerged as a huge problem in human medicine, particularly because of the development of highly drug-resistant strains. The disease is caused by the organism Mycobacterium tuberculosis. It can be spread through the air over short distances by minute droplets when someone with active TB coughs, sneezes, speaks or sings. Other individuals become infected by breathing in the bacterium.
Tuberculosis is primarily a human disease. It has been reported in various animal species, but only rarely. Dogs are considered relatively resistant to TB, even so there are several reports in the scientific literature of TB in dogs. The source of the dog's infection in this case was not discussed. Presumably, the dog was infected by close contact with an infected person.
One of the reasons for euthanasia of the dog in this case was the risk to household members. At this point, we have little information about the risk that infected animals pose to their human contacts. This makes providing evidence-based advice difficult. Many people may err on the side of caution by euthanizing the animal to prevent transmission. Important aspects that need to be considered include whether the owner can afford to attempt treatment of the animal (with no clear evidence of what works and longterm treatment being required), whether the disease is potentially treatable (i.e. what are the chances the animal will recover if it is treated), and the status of other household members with respect to TB disease or exposure. Of course, these consideration are all in addition to that of the animal's condition and quality of life, which may warrant euthanasia regardless - tuberculosis can be a devastating disease, and it is often not detected until it is quite advanced.
There's no correct answer. Our poor understanding of this disease in dogs and the significant health risks of TB in people unfortunately make euthanasia a reasonable decision.
Animal smuggling - Do you know where that pet came from?
Animal smuggling is a surprisingly big problem. A report in the Canberra Times quotes an Australian customs officer as saying animal smuggling is a $20 billion industry and the third largest criminal activity in the world (after drugs and weapons).
Animal smuggling can range from someone trying to sneak an exotic pet into the country, or large- scale smuggling by certain individuals (like the guy who tried to smuggle 300 poisonous frogs onto a plane). It can also consist of massive organized crime ventures.
There are many concerns associated with animal smuggling:
- Animal welfare: High death rates are not uncommon among animals during illicit transportation. Smuggled animals are often wild-caught, and even if they survive the stress of transportation, they may die soon after arrival. Particularly when you hear about animals being smuggled sewn up in giant teddy bears, or stuffed into pockets and pouches, it's a wonder as many of them survive as they do. The customs office in the Canberra Times article sums it up nicely "'People who smuggle animals don't care about the animals ... They actually see dead animals as an overhead.'"
- Introduction of foreign diseases: Smuggled animals have been blamed for introduction of serious diseases like avian influenza into areas where these diseases don't normally exist. This can be a huge problem, as it creates the potential for large outbreaks amongst indigenous animals or people whose immune systems are completely naive to the diseases.
- Transmission of disease to new owners: Smuggled animals certainly have not undergone good health examinations and quarantines, and can carry a host of potentially harmful microorganisms. This can put buyers and their families at risk.
Despite being a huge industry, there are things that everyone can and should do to reduce animal smuggling:
- Don't buy animals that you know were or may have been illegally imported. Doing so contributes to the death of countless other animals for every animal that survives.
- Don't buy wild-caught animals like birds and reptiles. Wild caught doesn't mean smuggled, but it may be hard to tell the two apart. Some of the disease risks, particularly to individual buyers, are the same with legally and illegally imported wild-caught animals. These days there are good, reputable and ethical breeders of many animal species around that can supply animals. If the species is so rare that there aren't any good breeders around, then don't buy it. It might be rare because the animals don't survive well in captivity, or are hard to find in the wild. You don't want to contribute to either of those situations. In some instances, you can find both wild-caught and captive-bred animals for sale. While the captive-bred version will almost certainly be more expensive, the extra cost is not so great when you consider the overall lifetime costs of the animal. And how much money do you really save if you end up with a sick or dead animal?
- If a deal sounds too good to be true, it probably is. That animal that you're getting for such a "great deal" might have been smuggled or be otherwise unhealthy.
- If, for some reason, you are determined to get a wild-caught animal, make sure that it comes from a reputable source who imported the animal legally. Ask how it was caught, stored and transported. A good supplier should be able to tell you everything that happened from the time of capture to its arrival, or at least be able to find that out. If they don't know or don't care, walk away.
Cat Scratch Disease - Bartonella henselae
Bartonella henselae is a small, Gram-negative bacterium that is host-adapted to cats. It may rarely cause mild illness in cats, but most felines, from tiny house cats to the king of the beasts, carry the bacteria with no clinical signs whatsoever. Unfortunately, when B. henselae infects a person it can cause any of several serious conditions (most of which have very long names!). These include bacillary angiomatosis (formation of masses of abnormal blood and lymph vessels), endocarditis (infection of the lining of the heart), chronic lymphadomegally (enlarged lymph nodes), and pyogranulomatous lymphadenitis, better known as cat scratch disease. There are at least four Bartonella species (among many, many other Bartonella species) that can infect cats, but B. henselae is the most common. There are at least nine Bartonella species that can infect humans, seven of which are zoonotic.
Between 5% and 40% of cats in the USA have B. henselae in their bloodstream. It is most common in cats from temperate areas, and is much less common in Canada. Bartonella spp. live in the red blood cells of their host – quite a clever strategy really, because it makes the bacteria readily available to be picked up by vectors like blood-sucking fleas, it protects the bacteria from the hosts immune system so it can live there for a long time, and it may even partially protect the bacteria from antibiotics. Cats can maintain a waxing and waning infection for months or even years. The bacterium is transmitted between animals by the cat flea (Ctenocephalides felis felis). Studies have shown that transmission does not occur between cats kept in a flea-free environment. Some ticks may also be able to transmit the disease. Diagnosis in cats is difficult – blood culture is the most reliable means, but it is not always sensitive. Antibody production only confirms exposure but not active infection. Polymerase chain reaction is often faster but no more sensitive than blood culture. An effective treatment regimen to eliminate B. henselae infection in cats has yet to be determined.
Transmission of B. henselae from cats to humans is thought to occur through contamination of scratches and bites (broken skin) with flea dirt (i.e. partially digested blood from the infected animal that is excreted by fleas = flea poop). Infection in individuals with weakened immune systems can be extremely serious or even fatal. In otherwise healthy people, the infection tends to remain localized, but can still cause massive swelling and abscessation of local lymph nodes. The type of disease that occurs may depend on the strain of Bartonella involved.
There are a few simple steps people can take to decrease the risk of cat scratch disease. These are particularly important for individuals with compromised immune systems, in which infection can be much more severe:
- Keep your pets flea- and tick-free. Effective treatment and prevention products are available from your veterinarian.
- Avoid or prevent situations that may result in bites and scratches from your pet. There is more information about this on the Worms & Germs Resources page and in our archives. If you do accidentally get scratched or bitten, be sure to clean the wound thoroughly. Consider seeking medical attention for bites in particular.
- Be aware of where cats come from. Stray or shelter cats less than one year old are most likely to be infected with B. henselae.
It is also important to note that there is NO evidence that declawing cats decreases the risk of transmission of B. henselae to humans!
As a point of interest, Bartonella quintana (a human-adapted Bartonella species) was the cause of trench fever in World War I, and was transmitted by lice.
Transmission of tuberculosis between a man and his parrot
A recent article in the journal Avian Pathology describes a case of Mycobacterium tuberculosis, the cause of tuberculosis (TB), in a pet bird (African Grey parrot) and its owner. Mycobacterium tuberculosis mainly causes disease in people, but can sometimes be found in other animal species, including birds. In this case, the bird was presented to a veterinarian because it had a decreased appetite and nodules under its tongue. The bird was wild-caught in Africa 11 years earlier. The owner was treated for TB two-and-a-half years earlier. Apparently, the owner usually fed the bird pre-chewed food (don't ask me why), and the vets suspected TB because of this close exposure. Because of the severity of the disease, the bird was euthanized and TB was confirmed by culture and PCR.
Often, we get to a point like this where both an animal and person have been diagnosed with the same disease, and can't go any further in terms of determining how each of them got the disease, and if it was transmitted between them. Fortunately, the Mycobacterium tuberculosis isolate from the owner had been saved, and they were able to compare it with the strain found in the bird. They were same. This strongly supports the theory that TB was transmitted between the owner and the bird. However, that's as far as we can go with confidence. The authors hypothesized (reasonably) that since the owner was diagnosed first, and since TB is mainly a human issue and is rarely found in birds, that the person acquired TB from some source then infected the bird. Additionally, two other reports of TB in birds also stated that the owners pre-chewed the birds' food.
TB in birds (and pets in general) is rare, and people shouldn't panic about it. However, it is apparent that transmission between species can occur. Transmission from an infected person to a pet is more likely than the other way around, but both are certainly possible. It's a good reminder that people with TB who are considered infectious should take precautions around their pets, just like they do around other people.
...and pre-chewing food for your bird is probably not a good idea, either.
Big dog, little dog, same dose
Most pharmaceutical products are dosed on the basis of weight (e.g. milligrams of drug per kilogram of body weight). That means an animal twice the size of another gets twice the dose.
Other drugs (mainly chemotherapeutic drugs, like those used for cancer treatment) are dosed based on body surface area (e.g. milligrams of drug per square metre of body surface). With this type of dosing, large individuals get more than small individuals, but the differences are not as great as with weight-based dosing.
Vaccines are a different story. They are administered based on the "antigenic dose" which is independent of body size. Therefore, the same dose is required for an adult Bullmastiff and a young Chihuahua. While it may be tempting to split doses of vaccine between several animals, especially small breeds (and initially this may seem logical (based on their small size) to those who do not realize how the dose is determined), this may result in ineffective vaccination. Trying to save money by splitting vaccine doses can end up costing money through increased risk of disease. Always give the full dose of vaccine as described on the label.
This post originally appeared (in modified form) on www.equIDblog.com on January 4, 2009.
Cat attacks Santa: another reason to vaccinate indoor cats
I admit I was a little slow picking up this Christmas story, but it's still "entertaining" (for lack of a better word). I've never thought about it, but I guess there are certain risks associated with playing Santa for pet photos. I'm not one to take my pets for pictures with Santa, but many worthy groups raise funds this way. During one recent event, "Santa" was bitten by a less-than-cooperative feline named Benny, who apparently didn't appreciate being in the company of the dogs which had also come. To make things worse, Benny wasn't your average cat - he was a pixie-bob, a very large breed of cat that resembles the North American bobcat (but it is in fact an entirely domestic breed)(pictured at right, from NBC10). After the incident, Benny's owners apparently produced proof of rabies vaccination, and everyone seemed fine. Besides the rabies concern, cat bites are not necessarily innocuous and severe complications can occur. That's one aspect of the story which hopefully didn't develop.
My point in writing this is to reiterate (again) my frequent statement that people need to make sure that their pets are properly vaccinated, even those that stay indoors all the time. Indoor cats can still bite people that visit, they can be exposed to rabid bats, and they can (not infrequently) escape. In this incident, if the cat had not had proof of rabies vaccination, a long quarantine period or even euthanasia may have been required - certainly not what anyone expects from a Santa photo-op.
And... maybe it's not a good idea to take large cats into strange places surrounded by dogs and thrust them into the arms of a strange person...something to consider.
More information on rabies and cat bites can be found on the Worms & Germs Resources page and in our bites archives.
Echinococcus on the rise in Bashkiria, Russia
Echinococcus granulosus, the cause of hydatid disease/hydatosis in people, is on the rise in the Bashkiria (Bashkortostan) region of Russia. Fifty-three cases were identified in Bashkiria in 2008, 1.7 times the number of cases reported the year before. Over 500 cases of human infection with Echinococcus are reported in Russia annually.
The original article (translated from Russian) states that the people at risk are those in contact with cattle and other domestic animals. Echinococcus actually causes the same type of disease in cattle and livestock as it does in people – it forms slow-growing cysts in the lungs, liver or other tissues. When the cysts are small they usually don’t cause a problem, but eventually (sometimes even years later) they can grow to a size that interferes with normal organ and body functions. However, people do NOT become infected by contact with cattle, sheep or other intermediate hosts. The infection can only be spread to humans (and livestock) by the definitive host - dogs, including domestic dogs and wild canids. In dogs, the parasite lives in the intestine in the form of a tiny adult tapeworm, and the tapeworm eggs are shed in the dog’s stool. When the eggs are swallowed by an intermediate host, the immature form of the parasite penetrates the intestinal wall and migrates through the body tissues to the site where it ultimately forms a hydatid cyst. If the animal dies or is killed, and the cyst is eaten by a dog, then the cycle begins again.
The most probably reason for the increased number of human infections in this case is an increase in the number of dogs in the same area, particularly those used for herding sheep. This may be equivalent to the dog-reindeer cycle present in Siberia. Echinococcus infection in dogs can be treated with common deworming agents that kill other tapeworms, but it is likely that dogs in these areas are not dewormed as often as they should be to prevent this disease.
The article reiterates some sound recommendations for decreasing the risk of Echinococcus infection. These may sound familiar, because many of them also help decrease the risk of transmission of infectious diseases in general:
- Wash your hands after contact with animals.
- Wash your hands after working in orchards where cattle have wandered (not the most widely applicable recommendation for people living in North America, but is along the same lines as our recommendation to wash your hands after working outside, particularly with soil).
- Do not consume unwashed greens or vegetables (all fruits and vegetables should be thoroughly washed with potable water before being processed or eaten).
- Do not drink water from untreated sources.
More information about Echinococcus and other tapeworms is available in the Worms & Germs Archives.
Photo: Central Asian Shepherd Dog (Sredneaziatskaya Ovcharka), click here for source (Wikipedia).
Molecular Diagnostic Testing: Pros and Cons
An important step in diagnosing infectious diseases and determining the optimum approach to treatment and management is rapid and accurate diagnostic testing. Many different testing methods are used, particularly bacterial culture (at least for bacterial diseases). Molecular testing has revolutionized the field of microbiology, and is making inroads into the field of diagnostic testing. Polymerase chain reaction (PCR) testing is a very powerful tool that can be used to detect DNA or RNA from specific microorganisms. This technique can be very useful, but it can also be easily misused or misinterpreted.
The potential PROS of molecular diagnostic testing include:
- Rapid turnaround time: Testing can take as little as a few hours versus a few days for other tests like bacterial culture.
- Sensitivity: Organisms that are difficult or impossible to grow in a lab can be detected, and they can often be detected at lower levels than with other diagnostic methods.
The potential CONS of molecular diagnostic testing include:
- Sample contamination: This is a common concern with highly sensitive molecular tests - even a minute amount of contamination in the sample can cause a false positive result.
- Test inhibition: Samples from complex biological sites (e.g. stool) can contain substances that interfere with the many complex molecular reactions upon which the tests rely. Without good (and proven) methods to prepare the sample, this can result in a false negative result.
- Biologically irrelevant results: Some bacteria that cause disease are also commonly found as part of the normal microflora in healthy animals - simply finding it does not tell you that it is necessarily relevant to the problem. For example, Clostridium difficile can be found in the intestine of approximately 10% of healthy dogs and cats (or more, in some situations), but the diagnosis of C. difficile diarrhea requires detection of the bacterial toxins in stool samples, not just the bacterium itself. A molecular test that simply identifies the presence of C. difficile, even if it identifies strains that possess the genes to produce toxins, tells you nothing about whether the bacterium was actually producing toxins in the animal.
- Lack of validation: This is a common problem with many (if not most) molecular tests. Some companies, especially those that just run molecular tests, offer a huge array of completely unvalidated and sometimes illogical tests. It is also important to remember that tests must be validated for each species in which they are used - a test that works well in people will not necessarily work on a sample from a horse or a dog.
Molecular testing can be useful in some situations. If you are unsure, here are some things to ask the lab:
- Do they have a validated test that provides relevant results? If they don't have good data (ideally published data) that their test is useful, accurate and reproducible, I'd avoid it.
- Do they have a quality control program, which includes running positive and negative control samples with each test batch?
Finally, as with any test that we use in veterinary (or human) medicine, it's important to evaluate all results in the context of what is happening with the animal - treat the patient, not the test result.
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