Toxoplasmosis: The Facts

Toxoplasmosis is a fairly common zoonosis (a disease that can be shared between humans and animals); 30 to 40 percent of adult humans, and roughly the same percentage of cats, have antibodies that indicate prior exposure to the organism that

causes the disease. Nevertheless, theres still a lot of misinformation regarding toxoplasmosis. The disease poses a threat primarily to fetuses and to immunosuppressed patients, but an understanding of the organisms life cycle, how transmission occurs and can be avoided, and the signs of infection can greatly reduce the risk of serious disease.

Toxoplasmosis is caused by Toxoplasma gondii (T. gondii) – a single-celled protozoan parasite that is able to sexually reproduce in only one host – cats. The most common way for a cat to become infected with T. gondii is by ingesting the tissue cysts present in infected rodents and birds. Once these cysts are ingested, they are released into the lining of the stomach and intestine of the cat, where they begin to reproduce. These cells produce both tachyzoites and oocysts. Tachyzoites, the active, feeding stage of the parasites, spread throughout the body, cause a reaction of the immune system, and are then walled off as dormant cysts in muscle and nerve tissue. Unsporulated (noninfectious) oocysts are also excreted in the cats feces for a few weeks, before immunity is developed. (Once immunity is developed, the cat will no longer shed oocysts in the feces and wont be infectious.) Within one to five days, oocysts that have been passed in the feces will sporulate and become infectious. Oocysts can survive in the environment for months to years and are highly resistant to heat, drying and disinfectants.

It is believed that the most common mode of transmission for T. gondii (to humans as well as cats) is through the ingestion of tissue cysts in undercooked meat. Outdoor cats often eat infected rodents and birds, whereas humans may eat infected, undercooked meat. While pork and lamb are the most common sources, T. gondii can infect any warm-blooded animal. Infection is also transmitted through the accidental ingestion of sporulated oocysts. For example, the oocysts can enter the digestive system of a person who has direct physical contact with old cat feces (they must be “old” because it takes one to five days for the oocysts to sporulate and become infectious), either from scooping cat litter or from gardening without gloves, and then touches his or her mouth. Dr. Michael Lappin, DVM, PhD, co-chair of the American Association of Feline Practitioners Zoonoses Guidelines Committee emphasizes that it is virtually impossible to contract toxoplasmosis by petting a healthy cat, given their scrupulous attention to personal hygiene. The only way to become infected with T. gondii is to ingest it. A pregnant female who has ingested the parasite stands some risk of transmitting infection to her fetus.

Toxoplasmosis often goes undiagnosed because the signs of infection are usually mild and short-lived. In general, cats may experience fever, loss of appetite and depression, although the signs may be more serious in cats that are immunosuppressed (for example, if they have feline infectious peritonitis or are infected with feline immunodeficiency virus or feline leukemia virus). Signs are very similar for humans. There are several precautions that can be taken to help reduce the risk of exposure to T. gondii:

(8) Cover your childrens sandbox when it is not in use so that outdoor cats wont use it as a litter box.