Herd Health: What is Toxoplasma gondii?

Tuesday, December 2, 2008

Toxoplasma gondii is a microscopic parasite which can infect all warm-blooded animals, including humans. Cats are the most common carriers of Toxoplasma gondii and they shed infective parasite eggs (called oocysts) in their feces.
People can become infected if they don't wash their hands after they change cat litter or if they garden in areas where cats have defecated. People can also pick up the parasite by consuming infected game meat, such as bear. Pork is also considered to be an important source of Toxoplasma gondii infection in people.

What happens to pigs?
Pigs can become infected if they consume infected cat feces or feed or water contaminated by cat feces. Once eaten, the eggs "hatch" in the intestines and the parasites move into the pig's body to form microscopic cysts in the muscles. Because rodents can also carry Toxoplasma gondii, pigs can also become infected by eating infected rodents. Pigs infected with Toxoplasma gondii typically don't become sick, so it is impossible to know if a pig is infected.

What happens to people?
Pork can become a source of Toxoplasma gondii infection when people eat undercooked, infected pork or other foods which have become contaminated with raw pork through improper hand or utensil washing during food preparation.
In humans, the disease caused by Toxoplasma gondii is called toxoplasmosis. In healthy people, the immune system is usually able to control a Toxoplasma gondii infection and most people don't become sick. If a healthy person does become sick, the symptoms are usually very mild and flu-like.

However, people with compromised immune systems can experience severe symptoms,  including fever, headaches, blindness, changes in behaviour, seizures and coma. Also, women who become infected for the first time during pregnancy can pass the infection to their unborn baby. This can result in miscarriage, the birth of a stillborn baby or birth of a baby which develops damage to the eyes, brain or other organs.

What can be done to prevent it from spreading from pigs to people?

One of the easiest steps to take is to make sure that there are no cats in the pig barn. If it is not possible to keep cats out of the barn, make sure that only mature cats are allowed in and spay female cats to ensure that no kittens are born in the barn.

Kittens and young cats are more likely to shed the infective eggs than mature cats.  Provide litter boxes and make sure the cat litter is changed regularly so that cats don't defecate in areas where pigs may come in contact with their feces. Do not allow cats to have access to areas where feed is stored to prevent contamination of pig feed. Good rodent control is also important to reduce the possibility of pigs consuming infected rats and mice. BP

Beth Young is a post-doctoral researcher and Cate Dewey is a professor in the Department of Population Medicine, Ontario Veterinary College, University of Guelph