Animal Diseases Transmisible to Humans

People can catch some diseases from their pets. Have you heard of ringworm, toxoplasmosis or canine roundworms? All of these are zoonoses, a term for animal diseases that can be shared between animals and humans.

Rabies is the best-known viral zoonosis in Canada, and the most deadly. Rabies infects any warm-blooded mammal via bite wounds or saliva contamination of wounds or skin abrasions. Bats can transfer rabies via a bite, though some cases have been reported where no bite was known to occur, but the bat was known to be in the room with a sleeping person. Skunks and raccoons are common wildlife vectors for rabies, as are roaming, unvaccinated feral cats and dogs. Vaccination is very effective, and is mandatory for pets in many areas, and keeping your pet on a leash outdoors will help to prevent contact with roaming rabid animals. An animal with rabies may have the traditional "furious" aggressive form, but the disease may show up as an overly friendly animal, a dazed animal, (the so-called "dumb" rabies) or even a pet with an apparently paralyzed tongue (salivating, mouth and tongue drooping).

Ringworm is a skin disease that plagues cats especially. Although called ringworm, this condition is actually caused by a fungus that can spread to people. Humans with ringworm have red, scaly areas on their skin that are sometimes itchy and may have a traditional "bulls-eye" appearance. Though not a serious problem, ringworm needs to be treated.

Clearing ringworm from catteries or households can be very difficult indeed since cats can be asymptomatic (with no symptoms showing) carriers. The fungus spore form can also get into heating ducts, carpeting and furniture of the home and is quite resistant (lasts years). Many cats only display scurfy or scaly dandruff, with small patches of hair thinning or loss if they do show any symptoms at all.

Toxoplasmosis is a disease people can pick up from cats shedding the single celled parasite Toxoplasma gondii in the cat's stool. "Toxo" is a concern for pregnant women because it can cause serious birth defects or spontaneous abortion. Most people actually get infected with toxo by handling raw meat. Gardening in soil contaminated with cat feces or eating incompletely cooked meat are also important sources. Contact with the stool of infected cats is less commonly a source. All pregnant women should seek advice about this disease from their doctors and not clean the cat box during pregnancy as a precaution.

Cats normally only shed the organisms for a short period following the initial infection, and cat exposure to the toxoplasma organisms most commonly occurs in young, actively hunting, outdoor cats.

Pets commonly have large worms, called roundworms, living in their intestine. People who inadvertently consume roundworm eggs can be infected. Once the eggs reach the person's intestine, they hatch. The larvae produced by these eggs burrow into, and sometimes through the intestinal wall and migrate through the body. The migrating larvae cause disease if they migrate through the abdomen (visceral larval migrans). Blindness may result if the immature worms reach the eyes (ocular larval migrans).

Children are more susceptible to infection than adults because they play on back lawns and in sand boxes where contaminated stool is likely to be found. To reduce the risk of human infection, pets should be dewormed regularly.

Hookworm, another intestinal worm, can cause skin (cutaneous larval migrans) infection in people, but intestinal hookworm disease is extremely rare. Commonly, transmission occurs when children play barefoot in moist, contaminated soils.

Though the common tapeworm species are not considered significant zoonoses, hydatidosis or hydatid disease, caused by an uncommon tapeworm (Echinococcus granulosis), and found in wild and domestic dogs and cats causes significant human disease.

Lyme disease (Borreliosis) is a disease of dogs and wildlife infected with Borrelia bacteria via a bite from a tick vector. Lyme disease may cause arthritis, heart disease, and is limited to only a few geographic regions in Canada. It is uncommon unless the pet or person undertakes travel, particularly in higher prevalence areas such as the northeastern US.

Only recently has the agent causing cat scratch fever been identified, and in humans, this agent causes lymph node changes and ulcers at the site of entry. Cats may not show any signs of illness. As the name implies, the most common route of transfer is by a scratch, but contact with cats, or bite wounds are also considered effective paths of transmission.

Giardia, Salmonella, and Campylobacter are bacteria found in the intestines of some animals, and can cause human disease. Pets and livestock may shed some of these agents in the stool during clinical disease, in diarrhea, or in some cases, unaffected carriers may shed these in normal appearing stools. They may contaminate the environment, and transfer may be indirect via contaminated water, soil, or other means.