kitty conundrum part 2: petplan pet insurance examines toxoplasmosis

Posted by Dr. Kim Smyth on Oct 24 2013

In an earlier blog, I told you about an organism that causes big problems for cats called cytauxzoon. Today, we’re going to talk about another organism that can spell trouble for our feline friends: Toxoplasma gondii.

Toxoplasmosis is the disease caused by the protozoal organism Toxoplasma gondii. It can infect many species of birds and most mammals, including humans. But our feline friends are most notorious for the disease for one simple reason: the organism can reproduce in their intestinal tract.

Eggs are produced and passed in the feces of cats (and only cats), making wild and domestic cats the definitive host of Toxoplasma gondii. Any other species that becomes infected with the organism can develop tissue cysts, but the organism cannot reproduce.

Cats become infected by Toxoplasma gondii when they ingest infected animals, like birds and small mammals. The organism multiplies in the gastrointestinal tract of the cat and millions of eggs are deposited into the soil or litter box when the cat has a bowel movement. Infected cats can shed eggs anywhere from three to twenty days after being infected. Once outside the cat, the eggs become infectious within one to five days and can remain viable for months.

Clinical signs in cats vary. Some will have no signs, while some might have diarrhea. In other mammals, clinical signs will depend on the location and number of cysts involved in the disease. Intermediate hosts ingest infective eggs, which then begin a life stage called the tachyzoite stage. At this stage, the organism can spread through the body, causing tissue damage in major organs and muscle. However, adults with normal immune systems are generally able to control the spread of tachyzoites, driving them into a tissue cyst stage. The cyst stage generally causes subclinical disease.

Diagnosis is difficult. Biopsy or PCR tests on infected tissues may lead to a diagnosis, but often a diagnosis is reached by fitting together puzzle pieces such as clinical signs, medical history, or paired serum samples. You may be wondering why your veterinarian can’t just perform a fecal sample, as the eggs are shed in the stool. This is, of course, how other types of parasites are found, but remember that dogs won’t shed eggs and cats will only shed eggs for three to twenty days after infection.

If you are or have been pregnant, you’ve probably been warned against changing your cat’s litter box. You might have even heard the ludicrous suggestion that you have to give up your cats. Toxoplasmosis is behind these rumors. That’s because the Toxoplasma organism can cross the placenta, where it can cause miscarriage or stillbirth, blindness, or neurologic deficits to your unborn baby.

But when you stop to consider the facts, surely your mind will be at ease. Remember that cats are infected by ingesting other infected prey, and once infected, they only shed infective eggs in their stool for about two weeks. So if you have an indoor cat, it’s likely she’s never even exposed to the organism. And even outdoor cats are unlikely to shed eggs during your nine months of pregnancy. In fact, most cases of human toxoplasmosis are from eating undercooked meat.

However, just to be safe, wear gloves when changing the litter box. Or, even better, enlist the help of your partner to get out of the chore altogether!

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