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Eric Barchas, DVM is a veterinarian who lives and works in the San Francisco Bay Area. His emphasis is on small animal medicine, emergency medicine, hospice and wellness. An avid traveler, he has studied lions in Botswana and salmon in southern Chile.

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Toxoplasma gondii (Toxoplasmosis) in Cats

Animals Affected

Cats and humans

Overview

Toxoplasma is a microscopic parasite that is capable of infesting most mammals.   It causes no symptoms in the vast majority of infested hosts, including humans.  However, Toxoplasma can cause fetal malformation or miscarriage in pregnant women, and it can cause serious illness in human beings with AIDS.

Although Toxoplasma commonly infests a very wide variety of animals, the parasite is capable of completing its life cycle only in cats.  Infective Toxoplasma oocysts (eggs) may occur in cat feces.

Cats infested with Toxoplasma typically shed infective eggs for one period of 3 - 21 days during their lives.  Therefore, any given cat is very unlikely to pass eggs in its feces at any given time.  However, the eggs are very durable and persist in the environment for many months.

Animals (including humans) can become infested with Toxoplasma by consuming eggs that have passed in cat feces or by consuming meat that contains the parasite.  Most experts believe that the majority of human cases of toxoplasmosis occur as a result of exposure to the eggs in the environment, or as a result of eating undercooked meat that is contaminated with the parasite.  Because free roaming cats may defecate in gardens or sandboxes, people who frequent these areas are believed to be at increased risk of exposure to Toxoplasma.

This article is not intended to provide comprehensive details on the risk of Toxoplasma to human beings.  If you are pregnant or if your immune system is compromised, or if you have any questions about the parasite, talk to your doctor about toxoplasmosis.

Symptoms of Toxoplasmosis in Cats

The majority of cats infested with Toxoplasma show no symptoms.   It is believed that toxoplasmosis may trigger transient diarrhea in some cats.  Very rarely, Toxoplasma may spread widely throughout the cat's body, leading to neurological problems or death.  This occurs most often in cats whose immune systems are compromised by feline immunodeficiency virus or feline leukemia virus.

Risk Factors and Prevention in Cats

The main mechanism through which cats contract toxoplasmosis is consumption of prey animals that are infested with the parasite.   Therefore, cats that roam outdoors and cats that hunt are at increased risk of Toxoplamosis relative to cats that are kept indoors.

Cats that are fed raw meat may contract Toxoplasma through their diets.

Complications

As was mentioned above, a very small number of cats suffer serious illness as a result of toxoplasmosis.

Spread of the parasite to pregnant women or to AIDS patients is the most serious potential consequence of Toxoplasma.

Diagnosis of Toxoplasmosis in Cats

Toxoplasma eggs can be detected in the feces of cats that are passing them.  Since infested cats shed eggs for only a brief period of time, it is not common to find Toxoplasma eggs on fecal exams.

A variety of blood tests can determine whether a cat has been exposed to Toxoplasma. However, these tests do not provide insight into whether the cat may pass eggs into the environment.

Because Toxoplasma rarely causes symptoms in cats, tests for the parasite are rarely performed.

Treatment of Toxoplasmosis in Cats

Most cats with toxoplasmosis do not require treatment.

Follow-up

A cat that is infested with Toxoplasma typically sheds eggs for only one brief period during its life.  After this period, it is unlikely to become ill or to pose a risk to other animals.

Preventing Spread of Toxoplasma to Humans

Toxoplasmosis can lead to serious consequences in pregnant women and AIDS patients. Experts believe that the majority of human cases are not the result of the parasite spreading from pets to owners.  Rather, most human cases appear to be caused by eating undercooked meat or shellfish, or by eating unwashed vegetables that are contaminated with Toxoplasma eggs, or by working with soil (especially in gardens) that contains parasite eggs.

Nonetheless, cat owners can take steps to reduce the likelihood of contracting the parasite from their pet.  Pregnant women and people with compromised immune systems should avoid cat feces.  Toxoplasma eggs that pass in cat feces generally are not capable of infesting human beings until 24 hours have passed.  Therefore, the risk of infestation is reduced if litter boxes are thoroughly cleansed at least once daily.

Hands should be thoroughly washed after handling cat feces, or after handling soil (such as garden soil) in which free roaming cats may have defecated.   Meat and shellfish should be thoroughly cooked and vegetables should be thoroughly washed before being consumed.

Maintaining good personal and household hygiene as described above reduces the risk of human toxoplasmosis dramatically.

Although these precautions are considered especially important in AIDS patients and pregnant women, they are sensible recommendations for all people.  Recent research has suggested a link between Toxoplasma infestation and schizophrenia in humans.

Miscellaneous

Toxoplasmosis is believed to be a leading threat to the survival of the California sea otter. Eggs in the feces of free roaming cats appear to wash into the ocean and infest the otters.

This article drew on information from JAVMA vol. 231 (Dec. 1, 2007) p. 1650 and pp. 1676 - 1684.

Copyright © Eric Barchas, DVM. All rights reserved.
The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.