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Toxoplasmosis is a disease caused by Toxoplasma gondii (T. gondii). This parasite can infect all warm-blooded animals, including humans. Cats are involved in the life cycle of this parasite, but rarely show any clinical signs. The life cycle begins with a cat eating infected prey animals or raw meat. Once the meat is ingested, T. gondii breaks free from cysts and starts to form eggs, which are called oocysts, in the cat’s gastrointestinal tract. The oocysts are excreted in feces, and these eggs are stable in the environment and can tolerate harsh weather for months.
This cycle is not particularly harmful for cats. Some of the cysts will form deeper in the cat’s intestinal layer and multiply, which are known as tachyzoites. Tachyzoites can spread from the intestines throughout the body of the cat. They can form cysts in the cat’s muscles or brain and slowly multiply, which is referred to as a bradyzoite.
The oocysts that are defecated by the cats then sporulate in the environment, which is a process that usually takes 1 – 5 days. Once the oocytes have sporulated, they can be infectious to other animals and humans. The main form of infection is through handling cat feces in a litter box or in soil. The oocysts are inadvertently ingested by humans or purposefully ingested by other animals. Sporulated oocysts create cysts in various tissues throughout the body. Goats and cows can shed T. gondii tachyzoites in their milk if infected.
Symptoms of Toxoplasmosis
Clinical signs are most commonly seen in cats with impaired immune systems, such as those with feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV).
- Breathing abnormalities/pneumonia (if cysts are in the lung tissue)
- Icterus or jaundice (if cysts form in the liver)
- Uveitis (inflammation in the anterior chamber of the eye)
- Neurological abnormalities, including seizures, tremors, blindness, and circling
- Acute death (seen most frequently in kittens infected in utero)
This infection is diagnosed by a combination of clinical signs, physical exam findings, and further laboratory diagnostics (like antibody testing). IgG antibodies can be seen in a cat that has previously been infected and has an immunity to the parasite. Presence of IgM antibodies is indicative of an active infection. Polymerase chain reaction (PCR) testing can also be used to detect an infection in a symptomatic cat, and is often used in conjunction with antibody testing.
Treatment of Toxoplasmosis
Treatment in cats involves symptomatic care based on clinical signs. This involves IV catheter and fluids, anti-nausea medication, and generalized supportive care depending on the severity of symptoms. Mainstay treatment of this infection is done with antibiotics like clindamycin or azithromycin. Clinical signs should start to show improvement in the first 2 – 3 days of treatment. Prognosis is generally considered good, but cats with liver and lung involvement can have a more guarded prognosis.
Preventative Measures for Cats
Prevention is important to minimize a cat’s exposure to this parasite. This includes limiting their access to infected prey and raw meat. Balanced, fully-cooked, commercially-prepared diets are recommended. Limiting rodent exposure and consumption can limit risk of infection. Cats should be encouraged to use a litter box indoors that is cleaned regularly to minimize outside defecation.
To minimize human exposure, litter boxes should be cleaned daily, since it takes less than 2 days for sporulation to occur. Thorough hand cleaning should be practiced after emptying the litter box to prevent inadvertent exposure. When gardening or working in soil that cats have frequented, gloves should be worn and hands should be washed afterwards. People who are immunosuppressed, including pregnant women, should limit litter box exposure and practice hand hygiene if exposed to cat feces. It was previously thought that immunosuppressed and pregnant women should not be around cats at all due to risk of toxoplasmosis, but that is no longer the CDC’s recommendation.