Transmission of tuberculosis to pets
Some people consider tuberculosis to be a disease of historical interest, but TB is alive and well, and spreading. TB is caused by Mycobacterium tuberculosis, a microorganism that can cause severe lung disease. TB rates are climbing rapidly in some countries and the emergence of highly drug resistant strains is a major concern. Anytime infectious diseases become more common in people in the general population, there is the potential for exposure of household pets. Recently, transmission of TB from humans to different animal species, including a dog, was reported. This follows earlier sporadic reports of TB in dogs. Finding TB in pets, albeit a small number, raises concerns about the potential role of pets in transmission of TB back to people.
Diagnosis of TB in pets is not particularly surprising, since it has been clearly shown by a few other infectious diseases that disease trends in people can sometime be reflected in their pets. It's hard to say if this is an under-recognized problem, an emerging problem or a very rare event that gets a lot of publicity. Really, the only way to tell will be to see what happens over time. Currently, TB is very rare in pets so it is important to keep possible risks and concerns in perspective. There is no reason for pet owners with TB to give up their pets. People with active TB should consider their pets as part of the family, and interact with them as they have been instructed to with people (i.e. if they are supposed to avoid close contact with people they should do the same with their pets).
There is currently no indication that infected pets can transmit TB back to people, and the risks are probably very low. TB is most easily spread through coughing, and pets with TB rarely develop respiratory disease with coughing. That, combined with the rarity of TB in pets, means that the risk of acquiring TB is much, much higher from other people than from pets.
This is just one more example of the "one medicine" concept, whereby we need to break down the barriers between 'animal diseases' and 'human diseases' (because the bugs are clearly doing so).
Banning Bowser from the beach
Many dog owners love to take their canine companions to the beach with them during the summer. Unfortunately, other people (particularly non-dog owners) sometimes take exception to having Bowser on the beach. These individuals often cite potential infectious disease risks as a reason to ban dogs from the beach.
While there are some potential infectious disease risks associated with having pet dogs at the beach, they are minimal. Also, some simple, common-sense steps can greatly reduce the risks that do exist. The infectious disease risks from feral (wild) dogs and wildlife defecating in the sand are much greater.
- The biggest health risk is actually probably from dog bites. Bites can be avoided through proper handling and training of dogs that are brought to public beaches.
- Many different bacteria (e.g. Salmonella, Campylobacter) can be passed in the stool of even healthy dogs. Some of these can be harmful to people, but only under certain circumstances, such as if they are swallowed or if they contaminate an open wound.
- Promptly picking up any stool passed by a dog greatly reduces the risk of significant contamination of the sand. Also, sunlight is an excellent “disinfectant” and will help kill any residual bacteria left behind.
- Dogs can also have different kinds of zoonotic parasites in their stool.
- Some of these parasites (e.g. roundworms, hookworms) are passed in a form that takes days to become infectious to people. So promptly removing dog stool from the beach minimizes the risk of transmission.
- Other parasites, such as Giardia, are immediately infectious when passed in the stool, but must be swallowed to cause infection. Prompt removal of dog stool, good hand hygiene with soap and water or an alcohol-based hand sanitizer before eating, and avoiding sand contamination of food and drink should largely eliminate this risk as well.
Overall, the risks of having dogs on beaches are very low if people behave responsibly, specifically properly restraining their dogs and promptly picking up stool.
More information about zoonotic diseases associated with contamination of sand and Sandboxes is available on the Worms & Germs Resources page.
Listeriosis outbreak in Canada: are pets at risk?
An ongoing outbreak of listeriosis in people in Canada has been linked to prepared meat products from Ontario. At least six deaths have been reported, and others are under investigation. While it is unlikely that there has been widespread exposure of dogs and cats, it is certainly possible that some pets were fed the recalled (and potentially contaminated) meat.
Listeriosis is an infection caused by the bacterium, Listeria monocytogenes. It can affect many animal species, but it is rarely identified as a cause of disease in dogs and cats. When signs do occur, fever, diarrhea and vomiting are most commonly reported. Rare cases of neurological disease in dogs and cats, and one case of suspected miscarriage in a dog due to listeriosis have been reported. Listeria skin infection has also been reported in dogs.
Overall, the risk of listeriosis in pets associated with the tainted meat products is very low. Pets that ate any of the recalled food products do NOT need to be tested or treated if they are not ill. However, should a pet that ate recalled meat become ill, it is important to inform the animal's veterinarian about the potential exposure to Listeria.
Eastern equine encephalitis in Ontario
A horse in Ontario was recently diagnosed with Eastern Equine Encephalitis (EEE), a serious neurological disease caused by a virus of the same name, which is transmitted by mosquitoes. The horse was from the North Durham region. The last reported cases of EEE in Ontario were in 2004. A few weeks ago, the Worms & Germs Blog talked about a large number of cases of EEE that have been reported in Florida this year.
Here are some of the key points to remember about EEE:
- Like West Nile, EEE is a seasonal disease. It is more common in warmer areas, especially some regions of the southeastern US. It is rare in cooler climates, but occasionally EEE is found in horses in Ontario.
- EEE is usually fatal in horses, and there is no effective treatment.
- EEE can also occur in people, and can be fatal in some cases.
- Infected horses cannot transmit the EEE virus to people, but if a horse gets EEE from the mosquitoes in the area, then people could also potentially be exposed to the virus by mosquitoes.
- A vaccine for EEE is available for horses, but most horses in Ontario are not vaccinated for EEE because it is so rare. Nonetheless, vaccination can be considered because the disease is so devastating when it occurs.
- As for West Nile virus, avoiding mosquitoes - for both horses and people - is an important preventative measure for EEE.
For more information, see the Worms & Germs Blog post "Eastern Equine Encephalitis – Not Just For Horses", or the CDC's website on arboviral encephalitides.
Are pregnancy and cats compatible?
.jpg)
There is a degree of risk of disease transmission from any contact with an animal, just as there is from any contact with another person. Some of the diseases involved are minor or even insignificant, while others are potentially devastating. And the risk can change in certain situations, such as pregnancy. A developing fetus is more susceptible to some diseases that may typically have little to no effect on an adult. Toxoplasmosis is one disease that gets a lot of attention from pregnant women.
Toxoplasmosis is caused by the protozoal parasite Toxoplasma gondii. Infection of a pregnant woman with Toxoplasma can cause birth defects or even miscarriage. But the real risk occurs when a woman who has not been previously exposed to Toxoplasma becomes infected during pregnancy. Pregnant women who were exposed to Toxoplamsa before they became pregnant, and therefore already have antibodies against the parasite, are not at risk.
Cats are the only animal species that can spread Toxoplasma in their stool. Only a very small percentage of cats are shedding Toxoplasma at any one time, but the proportion can be higher among cats that go outside, hunt or are fed raw meat. It takes 24 hours or more for Toxoplasma in cat stool to become infectious - a person cannot be infected with Toxoplasma from fresh stool. This key point can greatly reduce the risk of transmission from a cat, if the cat's litter box is cleaned out on a daily basis.
Any infection that can potentially have devastating effects on a fetus needs to be taken seriously. While it appears to be rare these days, some women are still advised to get rid of their cats if they are pregnant. Pregnant women do not need to give up their cats! A few basic measures can greatly reduce the risk of transmission of Toxoplasma from cats to pregnant women:
- Pregnant women should not have contact with litter boxes (or any cat feces) if possible - preferably another person should do the litter box cleaning.
- If a pregnant woman must clean the litter box, it should be done daily so that Toxoplasma does not have enough time to become infectious.
- Litter boxes should be regularly scrubbed and cleaned with scalding water (see the Worms & Germs Resources page for more information on Litter Boxes).
- Keep your cat's fur free of stool contamination. This is especially important in longhaired cats that might get stool on the fur around their hind end, or sick/old/obese cats that have difficulty grooming themselves properly.
- Keep your cat indoors. Outdoor cats are more likely to be exposed to Toxoplasma and spread the infection.
- Do not feed your cat raw meat.
- Wash your hands thoroughly after cleaning the litter box, handling raw fruit and vegetables, and working with soil (for example, in the garden).
- Cook all meat completely to recommended temperatures, and practice safe meat handling to prevent spread of contamination from raw meat to kitchen surfaces and other food.
More information about Toxoplasma and zoonotic diesases associated with Cats can be found on the Woms & Germs Resources page.
Antibody titres versus vaccination: the rabies debate
Rabies is an important disease that is almost always fatal. An important part of rabies control programs is mandatory vaccination of pets such as dogs, cats and ferrets. In general, rabies vaccination is very safe and effective. Complications from rabies vaccination are rare, but in recent years concerns have been raised about vaccine-associated sarcoma, a type of tumour that can develop at the site of vaccination. Since this complication was recognized, the vaccines themselves and the way they are administered have been changed in order to decreased the likelihood of this problem occuring, but the risk cannot be eliminated completely. For this reason, some people have tried to avoid having their pets vaccinated for rabies.
A.jpg)
blood test can be performed to determine antibody levels (also called a titre) against rabies virus. However, there is not enough information available to determine what antibody titre is high enough to say that an animal does not need to be re-vaccinated. Skipping rabies vaccination based on blood test results is dangerous and not recommended. While rabies is uncommon in most areas, exposure can occur, even in strictly indoor animals (e.g. if a bat gets into the house). Rabies vaccination is a legal requirement in most areas of Ontario. The implications of rabies exposure in an animal that is not "up-to-date" on its vaccines can be severe, including prolonged quarantine or euthanasia. I do not know of any jurisdictions that allow rabies antibody levels to be used in place of vaccination, and animals that are not recently vaccinated are treated as non-vaccinated, regardless of their antibody titre. The risk to your family or your pet from rabies is greater than the very tiny risk of vaccine-associated sarcoma. If you care about your pet and your family, make sure your pet is properly vaccinated against rabies.
More information about rabies can be found on the Worms & Germs Resources page.
Protecting your horse and yourself from West Nile virus
In Ontario, and many other regions, mid-August is the beginning of the high risk period for West Nile virus infection in people and animals such as horses. The Ontario Veterinary College has published an informational video on YouTube. This video has information about measures you can take to reduce the risk of West Nile virus exposure and disease, for both people and horses. Click on the image to watch the video. More information about West Nile virus is also available in the blog post entitled West Nile virus in dogs and cats.
"Clostridium" in dogs and cats: what's in a name?
People often ask me questions about "Clostridium" in dogs and cats, with the impression that "Clostridium" is a specific disease. Actually, Clostridium is a large bacterial genus (a group of related bacteria), which includes species that range from harmless to deadly. Some of the more important species are described below:
Clostridium perfringens: This is a common bacterium that can be found in the stool of a large percentage of healthy animals and people. It is a common cause of "food poisoning" in people, and is probably an important cause of diarrhea in dogs and cats. Our understanding of the role of this bacterium in disease in dogs and cats is limited by the fact that it is found in so many healthy animals, so simply growing it from the stool of a diarrheic dog or cat does not prove that it is causing the animal's illness.
Clostridium difficile: This bacterium is a very important cause of diarrhea (and more severe intestinal disease) in people, and is possibly an important cause of diarrhea in dogs and cats. It is rarely found in healthy adult pets, but is relatively common in puppies and kittens.
Clostridium botulinum: This bacterium produces the toxin that causes botulism, a potentially devastating disease that is very rare in dogs and cats. Botulism usually occurs following ingestion of food that has been improperly stored, in which C. botulinum has grown and produced its potent toxins.
Clostridium tetani: This bacterium produces the toxin that causes tetanus, which can occur in dogs and cats, however these species are relatively resistant to this disease. Tetanus usually occurs when a wound becomes contaminated with C. tetani from the soil, followed by growth of the bacterium and production of potent toxins.
Other clostridia: A large number of different species exist, and it is likely that many more clostridia are around but have not been identified and named. Many clostridia are part of the normal bacterial population in the intestinal tract. Some of these can probably also cause disease.
As you can see, "Clostridium" is more than a single bacterium or disease. An understanding of this concept, and the different disease-causing clostridia, is important. More information on Clostridium difficile can be found on the Worms & Germs Resources page.
Image: Photomicrograph of C. botulinum stained with Gentian violet. From CDC's Public Health Image Library (PHIL), ID number #1979.
Snakes, mice and Salmonella: a bad classroom combination
Reptiles are common pets, and the risk of transmission of Salmonella from reptiles is fairly well known. Most of the attention regarding Salmonella in these cases involves direct contact with reptiles, especially turtles. However, both direct and indirect contact with other reptiles also carry risk, as can contact with other animals. A recent report about a 2005/2006 outbreak of salmonellosis in 4 people from Minnesota highlights this:
- Three affected people were from the same junior high classroom, which contained pet snakes.
- Two of the people reported contact with the snakes, and one other student from the school did not handle the snakes but was often in the classroom, while the fourth infected student had a sibling in the class.
- The same Salmonella Typhimurium strain was found in the classroom snakes, various classroom surfaces and vacuum-packed rodents that were purchased over the internet and fed to the snakes.
- Presumably, the snakes became infected from the rodents, and the students became infected from handling the snakes, or from touching contaminated surfaces in the classroom (they reportedly had no contact with the rodents).
A broader US investigation identified 7 other people infected with the same Salmonella strain from handling vacuum-packed rodents. The outbreak was eventually traced back to the (unlicensed) rodent supply facility.
Pets can be educational and entertaining in classrooms, however some pets are better than others. Educational value, ability to properly (and humanely) care for the pet, and classroom safety need to be considered when determining what pet might be appropriate. Careful consideration of measures to reduce the risk of disease transmission is required. The teacher in this case reported that he did not know snakes could carry Salmonella, that he did not wash his hands after cleaning the cage, and that he did not tell students to wash their hands after touching the snake, so it is clear that there was inadequate consideration to these issues.
This case report also highlights the potential risks of reptile ownership in households. Reptiles are high risk for Salmonella, and not appropriate for all households. Good hygiene should be used when handling reptiles, their environment and their food. More information about reptiles can be found in the Turtles information sheet on the Worms & Germs Resources page.
Image: Corn Snake (Pantherophis guttatus) by Mike Wesemann
Pet treat danger
Pet treats derived from raw animal products such as rawhides and pig ears (yes, pig ear treats are actually dried, raw pig ears) are widely available and commonly fed to pets, particularly dogs. Being a raw product, there is an inherent risk of contamination with potentially harmful bacteria such as Salmonella. In 1999, an outbreak of salmonellosis linked to contact with raw pet treats was identified in people in western Canada. A subsequent investigation found Salmonella in over 50% of pig ear treats and 38% of other animal-derived treats. Similar results were reported by a later study in the US, and other outbreaks of disease have been reported. In Canada, the pet treat industry and government groups met and made various recommendations to reduce the risk of contamination.
To evaluate the effect of these changes, a Canadian follow-up study was performed. Only 4% of treats were contaminated with Salmonella, which was a marked contrast to the earlier study. Even so, the fact that Salmonella was present in a detectable percentage of treats means that certain precautions are warranted.
- Always wash your hands thoroughly after handling pet treats such as rawhides and pig ears
- Avoid buying treats from 'bulk bins', as there may be an increased risk of cross-contamination between treats in the bin
- Buy packaged treats so that you don't have to touch them directly when buying them or bringing them home
- Never store treats in areas where other food is kept or prepared
- Ask whether the treats you are buying have been produced under the Guidelines for the Manufacturing of Natural Pet Treats for Pets. There guidelines were developed by the American Pet Products Manufacturers Association with input from the Food and Drug Administration (FDA)
- Avoid buying raw treats if you have young children or anyone with a weakened immune system living in the household, as these treats may pose a small but unnecessary risk of exposure to Salmonella
- Contaminated treats seem to be a bigger problem for people than pets, however Salmonella can also cause disease in pets. If your pet develops diarrhea after eating an animal-product treat, be sure you tell your veterinarian
Image: Pig ear dog treat from www.foodpoisonblog.com
Cows to vultures to dogs to rabies: unintended consequences
"Unintended consequences" are outcomes (usually negative) of a particular action that are unexpected. For example, in some areas, hospitals now receive decreased reimbursement for MRSA infections. This policy was meant to help encourage hospitals to reduce MRSA infection rates. However, there are concerns are that this has actually lead to decreased MRSA testing (and potentially compromised patient care), because if the MRSA infection isn't documented, payment will not be withheld.
Unintended consequences can be found in many diverse areas. An interesting example was recently published in Ecological Economics and reported by the Toronto Star. It described the unintended consequences that linked use of a cattle drug to rabies deaths in India. Here's here story:
- Didofenac is a drug that was routinely used in cattle in India
The drug is apparently highly toxic to vultures- Vultures fed on cattle that died of natural causes, but that had didofenac in their bodies
- Millions of vultures died, which led to a larger food supply for feral dogs
- It was estimated that this lead to 5.5 million more feral dogs in India from 1992 to 2006
- These additional dogs would have accounted for at least 38.5 million dog bites
- Rabies is a serious problem in feral dogs in India
- In India, 123 people die of rabies per 100 000 dog bites.
Putting these numbers together, the unintended consequences of didofenac use in cattle may have result in 47 000 human deaths from rabies and $34 billion in health care costs. There are a lot of assumptions in this report, but it is an interesting story and highlights the unpredictable nature of infectious diseases, and the varying effects that seemingly unrelated actions can have.
More information on rabies can be found on the Worms & Germs Resources page.
Coroner blames cat in owner's death from E. coli
.jpg)
The inquest was told that there were three main possible sources of E. coli: food, travel and animals. The coroner determined that the owner most likely acquired E. coli from handling the cat or cleaning its litter box.There is no indication why this conclusion was reached, and it seems to be a rather strange conclusion based on the reported information. There is no reported evidence that the same strain of E. coli was even present in the cat. I suspect that they are blaming the cat because there is no other obvious source (e.g. an identified foodborne outbreak of E. coli). I doubt the cat played any role in this person's illness.
The risk of contracting E. coli from contact with a cat is very low. However, common sense should be used when handling cats and particularly cat stool. The most important measures are avoiding contact with stool and appropriate hand washing after handling a cat or its litter. More information about litter box management is available on the Worms & Germs Resources page.
How did dogs get MRSA?
A common question from owners of pets infected with methicillin-resistant Staphylococcus aureus (MRSA) is "Where did it come from?" The answer is not completely clear, but evidence strongly suggests it probably came from humans. The MRSA strains found in pets are almost always teh same as those found in people (including people that don't have pets) in the same geographic area. This strongly suggests that the MRSA came from the same source. Considering the fact that S. aureus in general is much more common in humans than in pets, and how long MRSA has been around in people, and that MRSA can sometimes be found in both people and pets in the same household, it is very likely that MRSA can move between species and originally went from humans to animal.Even though MRSA in pets probably originated from people, now that it is in the pet population, pets can spread it to other animals and back to people. It is unclear how frequently this occurs - most people are still more likely to encounter MRSA from another person than from an animal.
The emergence and spread of MRSA in humans was largely driven by extensive antibiotic use in people. Once MRSA crossed over to pets, antibiotic use in these animals almost certainly played a role in helping MRSA spread in the pet population. Antibiotic treatment has been identified as a risk factor for development of MRSA infection in dogs, and for MRSA carriage in horses.
Prudent antibiotic use is likely the most important factor in reducing the risk of MRSA in individual pets. Using antibiotics prudently means doing things like:
- Only using antibiotics when they're really necessary
- Using the most basic antibiotic possible (instead of the fanciest or most powerful antibiotic)
- Finishing every prescription completely and as directed)
Q Fever - From goats to people (and pets!)
Q fever is an infection caused by the proteobacterial organism Coxiella burnetii. Although usually not very common, C. burnetii can be carried by sheep, goats, and cattle, as well as birds and even sometimes cats and dogs. Animals often show no signs of illness, although the infection sometimes causes miscarriage, particularly in sheep and goats. Coxiella burnetii is also transmissible to humans. People are much more susceptible than animals to disease from Q fever. Even so, only about 50% of individuals that become infected show signs of illness, which can range from flu-like symptoms to pneumonia and hepatitis (liver infection). About 1-2% of infections in people are fatal.
Infected animals shed C. burnetii in their stool, urine and milk, but the highest number of organisms are shed in birth fluids and placentae. Coxiella is able to survive very well in hot, dry soil, and when dust and dirt from contaminated areas are stirred up into the air, the organism can be inhaled. This is the most common means of transmission, although direct contact with an infected animal or its stool or urine can also transmit the disease. Transmission from drinking milk from an infected animal is very rare, but is more likely if the milk has not been pasteurized. Cats and dogs can be infected by and transmit C. burnetii in all the same ways (especially through birth fluids), but they very rarely get sick. Ticks can also transmit the disease.
Q fever is one of the most infectious diseases in the world. As little as one C. burnetii organism is enough to infect a susceptible person. There are a few things to keep in mind to help reduce the risk of being exposed to this pathogen:
- Only eat/drink pasteurized dairy products.
- The main risk from cats and dogs (especially cats) is when they give birth. If you have a cat or dog that has kittens/puppies, wear gloves if you have to touch the babies or any placentae. Afterwards, cleaning the area very thoroughly to physically remove any tissue or fluid residue is very important, because most disinfectants cannot kill C. burnetii. Always wash your hands thoroughly after handing newborn kittens or puppies.
- On dry, windy days, avoid farms or areas where sheep or goats are kept.
- Avoid sheep and goat farms during the lambing/kidding season.
E. coli and dogs
While E. coli can be a serious problem in people and some animals, it is usually not a major problem in dogs. E. coli can cause diarrhea in dogs - it is most often linked to a disease called granulomatous colitis that is classically found in Boxer dogs. However, it is not a common cause of disease nor is it often associated with hemolytic-uremic syndrome in dogs. The O157:H7 strain of E. coli is rarely found in dogs, although transmission to people from the small number of dogs it has been found in has been reported. Almost all of the dogs that were found to be carrying E. coli O157:H7 were from farms, where they were probably exposed to the bacteria by eating cattle manure. The risk of transmission of E. coli O157:H7 from dogs to humans is very low.
- Even though E. coli O157:H7 is very rare in dogs, a number of other kinds of bacteria that can infect people can be present in the stool of both diarrheic and healthy dogs.
- All dog stool should be considered potentially infectious. Avoid contact with dog stool, and always wash your hands thoroughly if you have direct or indirect contact with dog stool.
- Because E. coli O157:H7 can be found in raw meat, it is reasonable to suspect feeding raw meat to a dog may increase the risk that it will have E. coli O157:H7 in its stool.
- The most important things you can do to avoid E. coli O157:H7 are:
- Handle raw meat properly to avoid contamination of other foods and surfaces.
- Make sure you cook meat at an appropriate temperature and for an adequate amount of time.
- Handle raw meat properly to avoid contamination of other foods and surfaces.
Eastern Equine Encephalitis - Not just for horses
Over 50 horses have died from Eastern Equine Encephalitis in Florida this year. The disease, caused by a virus of the same name, affects the brain, resulting in a broad range of clinical signs from behaviour changes to blindness to irregular gait. The disease is also sometimes called “sleeping sickness” because some horses may become severely depressed, with low head carriage and droopy eyes, ears and lips. Almost all horses that develop neurological signs from this infection die. Only 35 cases were reported in Florida in 2006 and 2007 combined.
There are actually three related equine encephalitis viruses – Eastern, Western and Venezuelan – which are called EEE, WEE and VEE for short. VEE is found in South and Central America and Mexico, and occasionally in the southern United States, but has never been reported as far north as Canada (VEE is a reportable disease in Canada). It is unique among the three diseases as the only one in which an infected horse will carry enough virus in its bloodstream to infect a mosquito, which could then pass the virus on to another animal. The EEE and WEE viruses, just like the West Nile virus, do not reach high enough levels in the bloodstream of horses to do this. The mosquitoes usually pick up the viruses from passerine birds, which do not become ill from the viruses (unlike West Nile virus in birds from the family Corvidae).
People can also be infected by EEE, WEE and VEE. About 10 fatal cases of EEE in people are reported in the United States every year. But horses cannot transmit EEE or WEE to humans, even if they’re bitten by the same mosquito. A higher number of cases in horses, however, may mean a higher number of mosquitoes that are carrying the virus. There is no vaccine for these viruses for humans, but there are vaccines available for EEE, WEE and VEE for horses.
In the end, EEE is just one more good reason to make sure you wear mosquito repellent when you’re enjoying the great outdoors during the summer. Visit the Health Canada website for safety tips on using personal insect repellents. EEE is very uncommon in Ontario, but horses that live in or travel to the southern United States should be vaccinated. Talk to your veterinarian about whether or not your horse should be vaccinated. Remember that fly control is also important for our equine companions (and also helps protect them against West Nile!).
