Worms and Germs Blog : Animal Health & Diseases : University of Guelph : Ontario Veterinary College : Zoonotic Diseases : Guelph, Hamilton, Ontario

There was an interesting article in USA Today about the increasing recognition of the positive role that pets can play in patients recovering from serious disease, and how contact with pets can sometimes conflict with disease transmission concerns in these same patients. The attitude towards pet ownership among physicians is highly variable - some recognize the strong human-animal bond and its positive effects, while others see pets as unnecessary infectious disease risks. The infectious disease concerns are heightened in patients with compromised immune systems, to the point that sometimes people are told to get rid of their pets if they are severely immunocompromised.  However, more and more pet owners, veterinarians and physicians are beginning to question if this is truly the best approach.

The USA Today article describes the experiences of a cancer patient whose greyhounds were "banished to a caregiver on doctors’ orders". Considering she was at high risk for (potentially fatal) infectious disease because of chemotherapy, bone marrow transplant, stem cell transplant and immunosuppressive drugs, it’s not surprising that there was concern about the pets. After researching the risks, and measures she could take to reduce those risks, the patient convinced her doctors that the risks from her dogs were not as great as the benefits from having them around, and so the dogs returned home. While everyone’s relationship with their pets is different, the patient felt that the return of her dogs was an important step in her recovery, stating "There's no question that having (the dogs) with me these past few months made a huge difference in my recovery".

Infectious disease transmission from pets to people is certainly a real issue, and it is of particular concern in people with weakened immune systems. There is not, nor will there ever be, a "no-risk" pet. Every contact with a pet, just like every contact with another person, carries with it some degree of risk of disease transmission. What needs to be considered is the trade-off, the risks versus the benefits. In some people, the risks are greater than the benefits because of the severity of disease, type of pet, the person's ability (or more likely inability) to interact with the pet. In other people, especially those who have a very strong bond with the animal, the positive social and emotional benefits of pet ownership may greatly outweigh the associated disease risks. The article contains a great quote from Dr. Ray Pais, a pediatric hematology/oncology specialist, saying "Our young patients have already given up so much, I see no reason at that moment for them to also lose the dog."

People that have compromised immune systems need to have a serious discussion with their physician, veterinarian and family about the best thing to do with their pets while they are sick. While there is very little research in this area, taking a few common sense precautions should reduce the risks of disease transmission. These include:

• Avoiding contact with stool
• Frequent handwashing
• Preventing licking of the person by the pet
• Proper training to reduce the risk of bites and scratches
• Keeping cats indoors
• Following a good preventive medicine program for the pet

More information about Immunocompromised Pet Owners will be available soon on the Worms & Germs Resources page. The CDC also has useful information on its website about this topic.

Thanks to Dr. Doug Powell of Barfblog for forwarding this article.

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As we see more and more infections caused by antibiotic-resistant bacteria, we have to re-think our approach towards antibiotic therapy. This often involves using new drugs, but sometimes it also involves considering the use of older drugs that we haven't used very much for a long time.

One such drug is chloramphenicol. Years ago, this antibiotic was widely used, and is still used in people and animals in some situations. In some respects, it is a very good antibiotic - it is often effect against many bacteria including those that are resistant to many other drugs, such as MRSA and MRSI/MRSP.  Chloramphenicol can also be given orally, and it's relatively cheap. Unfortunately this drug can also be very toxic, both to the animals being treated with it and to people that come in contact with with it in the process. In some animals, chloramphenicol can cause suppression of the bone marrow, where red and white blood cells are produced. This is more of a concern with long term use, but if the bone marrow does become suppressed, stopping treatment with the chloramphenicol typically resolves the problem.  Unfortunately, this bone marrow suppression is much more of a concern in people - the supression is very severe, and can occur with exposure to even a very low dose (or probably single dose) of chloramphenicol.  This results in a condition known as aplastic anemia,  which it typically fatal.  Fortunately this reaction is very rare in people, but there is no way to predict who might develop this condition, and since it is usually fatal, we obviously need to be cautious about using this drug. In some countries, chloramphenicol use in banned in all animals. In many others, it cannot be used in food animals, but can be used in pets.

• Chloramphenicol should only be used as a drug of last resort. There are situations where it is useful and may be life-saving, but the human health risks cannot be overlooked.
• If chloramphenicol is being considered, it is critical that  people who would need to handle the drug understand the risk and how to safely handle the drug to avoid exposure.
• Chloramphenicol tablets should not be crushed or otherwise processed at home because of the potential for breathing in the drug when it is in powder form.

Direct contact with pills or liquids should be avoided by use of gloves or other safe handling practices.

• If a liquid form is used and is squirted onto food, the food bowl should be handled as if it is contaminated.
• If pills are being used, the animal should be observed to ensure that the pill is ingested and not spit up and left on the floor.
• Contact with the mouth and face and animals that are being treated with chloramphenicol should be avoided in case drug residues are present.

If people are unable or unwilling to follow safe handling recommendations, they should not use this drug.

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A report about the health risks in children associated with nontraditional pets was recently published in Pediatrics, the official journal of the American Academy of Pediatrics. The report also discusses diseases associated with animals in public settings such as petting zoos and pet stores.  Although contact with pets and animals can be beneficial to growth and development in children, it is very important to be aware of the risks associated with certain kinds of animals.  Physicians, veterinarians and public health personnel can help parents select appropriate pets in order to maximize the benefits while minimizing the risks to children.

One of the most important pathogens discussed in the report is Salmonella. Although Salmonella can be transmitted by many animal species, including traditional pets like dogs and cats, it is a particularly high risk with certain other kinds of pets, including reptiles, amphibians and baby poultry (chicks and ducklings). It has been estimated that direct or indirect contact with reptiles or amphibians is responsible for 6% of all sporadic Salmonella infections in the US, and 11% of cases among people younger than 21 years. There is also a relatively high risk of Salmonella transmission associated with animal-derived pet treats, such as pig ears, and raw meat.

The report makes several recommendations about how to reduce the risk of infection, injury and allergies from nontraditional pets, many of which you may have seen before on the Worms & Germs website. Just a few of these are:

• Always wash your hands after contact with animals, animal products or their environment, and after contact with animal-derived pet treats.
• Supervise hand washing for children less than five years old

Children less than five years of age and individuals with weakened immune systems should avoid contact with reptiles, amphibians, rodents, ferrets and baby poultry. These animals:

• Should not be kept as pets in households where children less than five years of age or individuals with a weakened immune system live.
• Should not be brought to childcare centres.
• Should not be allowed to roam freely in ANY house or living area.
• Should not be permitted in kitchens or anywhere food is prepared.

More information about Salmonella in pets and the risks associated with feeding raw meat and animal-derived treats to pets can now be found on the Worms & Germs Resources page.

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In some areas, pet vaccines are readily available from multiple sources, including the internet. Some people like to purchase vaccines and administer them to their pets themselves in order to save money. But are the cost savings really worth the risk? Here are some things to consider:

• Your veterinarian gets vaccines through a reputable distribution system, which ensures quality control, tracking of products and proper shipping and storage conditions. When buying elsewhere (especially the internet), you don't have the same level of assurance. Vaccines that have been improperly handled or stored may not be effective.
• Vaccines and drugs from some sources are of questionable quality, and you can't always be sure that you're actually getting what you wanted. Ineffective vaccines or contaminated products are a big concern. It's not saving you money if the vaccine doesn't work!
• While uncommon, vaccine reactions do occur. If your pet has an anaphylactic (severe allergic) reaction at a veterinary clinic, the chances that your pet will survive are much greater because the needed expertise, drugs and equipment are readily available. You don't have these things at your house.
• If your pet develops a problem associated with a vaccine administered by your veterinarian, the vaccine manufacturer may get involved and assist with the problem. This will NOT happen if you buy the vaccine from another source and give it yourself.
• Rabies vaccines MUST be given by a veterinarian. (In some areas it's illegal for a non-veterinarian to even possess rabies vaccine.)  A pet that has received a rabies vaccine by a non-veterinarian is considered unvaccinated by public health authorities.  If an unvaccinated animal is exposed to rabies, the repercussions may be much more severe, and may even include euthanasia.
• Vaccination is just one part of your pet's "wellness program." Some of the pressure for people to vaccinate their own pets is a failure of the veterinary profession to adequately emphasize the importance of preventive medicine, of which vaccines are just one component. Simply charging an owner for "annual vaccines" leads people to want to vaccinate their pets themselves because they can get the vaccines for much less money.  Veterinarians need to emphasize that what they are charging for (and what is the most important component of the preventative medicine program) is an annual physical examination and health consultation, and that only a small portion of the fee is for the vaccines.

Vaccination is a minor component of your pet's preventive medicine program. A careful physical examination and consultation about potential, developing and ongoing health issues are the most important parts of this program. Even if you vaccinate your pet yourself (which is still not recommended for the reasons above), it is still critical that your pet has an annual examination. It's better for your pet's health, and it can be easier and cheaper in the long run because problems can be detected and treated early.

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Ringworm infection is not caused by a worm at all - it's actually a skin infection caused by certain kinds of fungus called dermatophytes. The scientific name for ringworm is dermatophytosis, or dermatomycosis. Some of the more common zoonotic species of dermatophytes found in animals include Microsporum canis, Trichophyton verrucosum, T. equinum, and T. mentagrophytes. There are also some dermatophytes that are primarily transmitted from person to person that are not carried by animals. These include the fungi that cause athlete's foot and jock itch.

Like many fungi, dermatophytes grow best in warm, moist environments, but they can grow almost anywhere on the body. They tend to grow around hairs and in the superficial layers of the skin, and the infection can be quite itchy. A ringworm skin lesion tends to spread out from one point on the skin, causing hairloss as it progresses, resulting in a bald patch (see picture right). The outside (most active) edge of the infection often appears as a red ring, from which "ringworm" gets its name.  The centre of the lesion may begin to heal, and the hair may start to grow back, even as the bald patch gets bigger.  It may take anywhere from a few days to a few weeks for visible lesions to develop after a person or animal has been infected. (Photo credit: A. Yu, Ontario Veterinary College)

Ringworm is quite contagious. The fungi are present in the large numbers on hair and skin cells that are shed by infected individuals. People or animals can be infected through contact with these infected hairs and skin cells, either directly on the affected person or animal (i.e. direct contact), or on things like clothing, blankets, hairbrushes etc. that have touched the affected skin (i.e. indirect contact).

Ringworm occurs all over the world, but no one knows exactly how common it is because there are so many different kinds of fungus that cause it, it's not reportable, and many cases probably go undiagnosed. Signs of ringworm in animals are often the same as in people, however not every animal that is infected with ringworm develops signs of infection. It has been estimated that ~90% of cats that are carrying dermatophytes do not show any signs of infection, but they can still transmit the fungus to other animals and people. (NB: this does NOT mean that ~90% of cats carry dermatophytes!)  Almost any animal can be infected by at least one dermatophyte or another - cats, dogs, rabbits, rodents... even horses and cattle!

• Early identification of ringworm is important to reduce the risk of transmission to people and other animals. If your pet develops bald patches, particularly if they're itchy, it should be examined by your veterinarian to determine if a fungal infection may be present.
• If you or anyone in your household develops an area of skin that appears infected (especially if it appears as a red "ring"), keep it covered with a piece of clothing or a bandage and see your doctor.
• Most cases of ringworm can be treated with either topical (e.g. ointments) or oral anti-fungal medication.
• Clean your pet's grooming supplies (e.g. brushes, combs) regularly.
• Always wash your hands after handling your pet.

Watch for another Worms & Germs blog post about ringworm and how to clean up if you or your pet is infected, coming soon!  More information about ringworm and dermatophytes can be found on the CDC's Dermatophytes website.

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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

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You may notice a recurring theme in many of our posts and on virtually all of the information sheets on the Worms & Germs Resources page: an emphasis on handwashing. There is increasing emphasis on hand hygiene (i.e. hand washing and use of alcohol hand sanitizers) education in hospitals because the hands of healthcare workers are a major (if not the most important) means of disease transmission between patients. Despite hand hygiene being easy, cheap and effective, people rarely wash their hands as often as they should, and they often don't do it properly.

Most of the research about hand hygiene that has been published has focused on its use and impact in human hospitals, but this area is now also being studied more with regard to animals and veterinary medicine. A study published earlier this year in Veterinary Microbiology provided more evidence that hand hygiene is a critical infection control measure when dealing with animals. The study, coordinated by Dr. Maureen Anderson (of Worms&Germs fame) looked at MRSA carriage rate in veterinarians who work with horses. In addition to finding a high rate of MRSA carriage among these veterinarians (which was consistent with other reports indicating that equine vets are at higher than average risk for exposure to MRSA), the study looked at factors associated with MRSA carriage. Vets that reported routinely washing their hands between farms and those that reported washing their hands after contact with potentially infectious cases had a significantly lower rate of MRSA carriage. That should come as absolutely no surprise, but it's one more piece of evidence that we need to pay more attention to this routine infection control measure, in human hospitals, in veterinary environments and in households.

Remember, the 10 most important sources of infection are the fingers on your hands!

Click here for instructions on how to wash your hands properly.

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