Toxoplasmosis is caused by the microscopic parasite, Toxoplasma gondii. This parasite can infect almost all mammals including humans, but domestic cats and their wild relatives are the definitive hosts (i.e. the parasite requires a cat to complete its life cycle). There are three main ways the parasite is transmitted to people and animals:
- Infection of a fetus during pregnancy
- Eating an infected tissue source (such as raw or undercooked meat)
- Ingestion of oocyst-contaminated food or water
Only domestic and wild cats shed the infective form of the parasite - the oocyst - in their feces. These oocysts can contaminate the environment as they are resistant to freezing and drying and most disinfectants. Once shed by the cat, they require from 24 hours to a few days to become infectious. When another mammal, such as a mouse, ingests the infectious oocysts, it then becomes infected with Toxoplasma. If the mouse survives the infection, it may become a source of infection for any animal that eats it. Cats usually become infected by ingesting the infectious oocysts or by eating prey or raw meat containing the parasite. Kittens may also be infected in utero if the queen acquires the parasite while pregnant.
The parasite initially infects the cells of the cat’s intestinal tract and the associated lymph tissue. It can then spread to other organs via the blood or lymph system. Once infected, cats begin to shed oocysts in their feces a few days to a few weeks later. However, oocysts are shed for only one to three weeks after the initial exposure, so most cats are
not shedding at the time they have signs of illness. Shedding is heaviest when kittens
aged 6 to 14 weeks old are infected.
Disease is most severe in those kittens infected before birth. These kittens can be stillborn
or may fail to thrive and die before weaning. Affected kittens may have inflammation of
the lungs, liver, and central nervous system. Fluid can accumulate in the abdomen. Cats
infected after birth may have clinical signs that include loss of appetite, lethargy, and
trouble breathing due to pneumonia. Other clinical signs can include fever, weight loss,
jaundice, vomiting, diarrhea, stiff gait, shifting leg lameness and neurologic problems.
Inflammation of the retina in the eye can also occur. .... [Read complete article]
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