A zoonotic disease is one that can be passed from pets to people. People often worry about the possibility of infection for themselves or family when a pet is diagnosed with intestinal parasites, such as worms. Unfortunately, this concern is valid, as there are several intestinal parasites that are considered to be zoonoses.
Roundworms, more properly known as ascarids, are one of the most common intestinal parasites seen in both dogs and cats. In fact, many–if not most–puppies and kittens are born with roundworms. They do, however, have the potential to be passed to people, and children are at highest risk for infection with roundworms.
Tapeworms also are considered to be a zoonotic parasite. However, they are typically not passed directly from pets to people, even though dogs and cats are commonly infected with them.
In order to infect a dog or cat, tapeworms require an intermediate host, which is usually a flea or a small prey animal that is ingested. The intermediate host is also necessary for transmission of tapeworms to people, and dogs and cats do not serve as intermediate hosts. However, eating uncooked meat or fish that is infected can pass certain types of tapeworms to people.
Trichinella spiralis is another intestinal parasite that has the ability to infect people. However, dogs here in the US are seldom the cause of trichinosis (infection with T. spiralis) in people. This disease is transmitted only by eating undercooked meat infected with the parasite, most often pork or game.
Another intestinal parasite that can be passed from people to pets is Giardia. Giardia is different from many other intestinal parasites because it's a protozoan, or a single-celled organism, rather than a worm. Nevertheless, it can infect both dogs and cats and can also potentially be passed to people.
Toxoplasma gondii, the cause of toxoplasmosis, is a parasite that is frequently found in cats. It can also infect people and can be quite serious under certain circumstances, particularly for a pregnant woman and her fetus. T. gondii is also a protozoan parasite and not a worm. However, pregnant women can take precautions to prevent toxoplasmosis by making sure their food is properly handled.
How Intestinal Parasites Are Passed From Animals to People
Intestinal parasites can be passed to people in several different ways. The primary means of transmission depends on the type of parasite.
- Some intestinal parasites can be passed to people through ingestion of feces from infected animals or ingestion of contaminated soil or water. Examples include roundworms, hookworms, Giardia, and Toxoplasma.
- Some can be passed when the larvae of the parasite contact uncovered skin. Hookworms can be transmitted this way.
- Other intestinal parasites are transmitted by eating uncooked or uncooked meat that is infected. Certain types of tapeworms, as well as Trichenella, can be passed in this fashion.
Fortunately, in most cases, infection with zoonotic intestinal parasites can be avoided by taking simple precautions like practicing good hygiene and making sure all meat is cooked thoroughly before eating.