This disease of cats and other mammals is caused by a parasitic protozoan, Toxoplasma gondii. Protozoa are single-celled organisms but are not in the same classification as bacteria. They are among the simplest creatures in the animal kingdom. Cats that hunt and consume raw meat will have the greatest chance for contracting Toxoplasmosis. Ingestion of tissue cysts in infected prey or in other raw meat is probably the most common route by which cats are exposed to Toxoplasma.
Although infection with Toxoplasma is fairly common in cats, actual disease caused by the parasite is relatively rare. Cats are able to shed Toxoplasma in their feces for a few weeks after they are first infected with the parasite. And as in humans with the disease, cats rarely have symptoms when first infected. A cat can remain healthy appearing and yet have the organism within their bodies. There are no good tests available to determine if your cat is passing Toxoplasma in its feces.
Acutely infected cats might display lethargy, depression, poor appetite, lesions in the retinas of the eyes, weight loss and fever. Liver and lung abnormalities may occur. Any cat that displays a brain disorder such as incoordination, sensitivity to light, constricted pupils, circling, personality changes or other central nervous system abnormalities should be evaluated for Toxoplasmosis.
Immunocompromised persons who are undergoing immunosuppressive therapy or those with an immunosuppressive disease such as AIDS should take special precautions against exposure to cat feces because of potential infection with Toxoplasma oocysts in the cat’s stool
Cats acquire Toxoplasma infection by eating any of the three infective stages of the parasite: cyst, oocyst, or tachyzoite. Following ingestion of the cysts in infected prey animals such as rodents or birds, the intra-intestinal infection cycle begins. This cycle occurs only in members of the cat family. The organisms multiply in the wall of the small intestine and produce oocysts for two to three weeks. The oocysts are then excreted in large numbers during this time is the cat’s stool. Within five days, if conditions are right, the shed oocysts can sporulate and become infectious for other animals and humans. Once sporulated, the oocysts are highly resistant to environmental conditions and can survive for many months.
Most healthy exposed cats shed oocysts during acute infection with Toxoplasma, but will not shed them after the acute infection is over. In a few cats that do re-excrete oocysts after another exposure to Toxoplasma, the number of oocysts shed is smaller and may even be insufficient to transmit the parasite effectively.
Congenital infection is much less common in cats than it is in humans and some farm animals. The diagnosis of Toxoplasmosis is challenging and requires serial sample of blood to see if the animal is developing immune proteins, which implies that Toxoplasma organisms are stimulating the immune system. Treatment for Toxoplasmosis generally entails administration of an antibiotic, or even two antibiotics at the same time, and is generally effective in arresting the disease in cats.At present there is no vaccine for Toxoplasmosis in cats. Because of the potential for human exposure to infective oocysts in an infected cat’s feces, special circumstance should be discussed with your physician if you are pregnant, immune compromised or are taking immunosuppressive medications such as anti-cancer medication or cortisone.