The common parasite Toxoplasma gondii can infect cats as well as people and other animals. Here’s what you need to know about treating and preventing toxoplasmosis in cats.

By Sarah Mouton Dowdy
August 24, 2020
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Yeji Kim

Toxoplasmosis is a serious and sometimes fatal disease that can affect cats, humans, and many other animals. It’s caused by a parasite called Toxoplasma gondii (known as T. gondii for short), but there’s a big difference between being infected with the parasite and actually having the disease. And while cats are the definitive hosts of T. gondii, it’s not dangerous to own or pet cats that are infected. Preventing the disease requires an understanding of how the parasite is transmitted to both cats and people. 

What is Toxoplasmosis in Cats ?

Toxoplasmosis is a disease caused by a combination of T. gondii and a suppressed immune system. “T. gondii is a type of single-celled parasite called a protozoa,” explains Leah Cohn, DVM, PhD, DACVIM, a professor of small animal internal medicine at the University of Missouri College of Veterinary Medicine in Columbia, Mo. “It’s not a bacteria. It’s not a virus. It’s not a fungus. It’s a protozoa, which is an entirely different kind of germ. On the scale of germ size, it’s a pretty hefty germ compared to teeny tiny viruses, but certainly smaller than a worm would be.” 

According to Cohn, it’s very common for cats to be infected with the parasite. They usually pick it up by eating infected meat from a mouse or rat. But being infected isn’t the same as having the disease, she says. In fact, a cat can remain healthy with T. gondii in its body. It takes a suppressed immune system for the disease to develop, which is why immunosuppressed cats are most at risk. Common causes of immunosuppression in cats include viral infections like feline leukemia (FeLV) and feline immunodeficiency virus (FIV), certain medications, and old age. 

How Can You Tell If Your Cat Has Toxoplasmosis?

According to Cohn, the signs and symptoms of toxoplasmosis in cats depend on which organs are affected by the parasite. “We can’t predict which organs will be impacted, but the brain, eyes, lungs, and liver are some of the most common and important sites of disease,” she says. Some of the most common signs include:

  • Difficulty walking
  • Seizures
  • Eye inflammation
  • Blindness
  • Difficulty breathing
  • Yellowing of the skin, indicating jaundice
  • Fever
  • Reduced appetite
  • Lethargy (decreased activity)

Can Humans Get Toxoplasmosis From Cats?

Toxoplasmosis is a zoonotic disease, meaning it can be passed from animals to humans, though Cohn says direct transmission from cats to humans is very, very rare. Much like in cats, T. gondii infection in people is common. The Centers for Disease Control estimates that 11 percent of the U.S. population aged six and older have been infected with the parasite. But again, it’s important to keep in mind that there’s a difference between infection and disease—most people who are infected don’t experience any problems. Similar to cats, those who have suppressed immune systems are most at risk for developing the disease.

There are two main ways people get the parasite, Cohn says: by eating the undercooked meat of an infected animal, and by accidentally eating a form of T. gondii that was living in the soil. Both of these sources can be traced back to cats because they are the natural hosts of the parasite. This means that cat intestines are the only place in the world the parasite can mate and produce baby T. gondii (called oocysts). 

These oocysts can be found in the poop of infected cats and are eventually deposited wherever else the cat decides to poop. Interestingly, these oocysts aren’t infectious until they undergo a process called sporulation, which takes at least 24 hours. Once sporulation occurs, the oocysts are infectious to anyone and anything that eats them, Cohn explains, and they stay infectious for a year or more.

So if, for example, a grazing sheep eats sporulated oocysts, becomes infected with T. gondii, and is later served undercooked at a restaurant, there’s a chance the person who eats it will become infected. (This is why restaurants have disclaimers on their menus about the risks of eating undercooked meat.) Or if a person who’s gardening forgets to wear gloves and doesn’t wash their hands before eating lunch, they could possibly transfer infectious oocysts to their sandwich and infect themselves. Unwashed fruits and vegetables that have been grown in infectious soil are another common infection route. 

Though it may seem like an obvious spot to pick up an infection, Cohn says it’s incredibly uncommon for people to become infected when emptying the litter box for three reasons. First, sporulation (the process that makes oocysts infectious) takes at least 24 hours to occur, and many people clean or empty the litter box every day. Second, most people wash their hands after completing the task. Third, infected cats only shed oocysts in their poop for the first two weeks after infection. After those two weeks are up, that cat’s poop will never again contain the parasite. T. gondii will be in its muscles, but not in its poop.

Can Humans Get Toxoplasmosis from Other Humans?

There is another way the parasite is transmitted to humans: from mother to unborn baby. “If a woman has T. gondii in her body before becoming pregnant, it won’t be a problem for her baby,” explains Cohn. “But if she becomes infected while pregnant, that’s when you can see miscarriage, stillbirth, or serious birth defects.” 

Women who are pregnant or are thinking of getting pregnant are encouraged to talk to their doctors and veterinarians about the risks. But they don’t need to automatically get rid of their cats.  

Cohn recommends that despite the low risk of transmission, pregnant women, as well as people with depressed immune systems (such as those with AIDS or organ transplant recipients), should have someone else empty the litter box. If that’s not an option, she says they should remove the poop every day and then wash their hands well. Another solution could be to use an automatic litter box cleaning system. 

Cohn notes that it would also be wise for these groups of people to be extra cautious when it comes to gardening, consuming undercooked meat, and eating fruits and vegetables that haven’t been thoroughly washed. Also consider wearing gloves while cleaning the litter box or gardening (and always wash your hands afterward). 

Transmission of toxoplasmosis is also possible, although unlikely, via organ transplantation or through blood transfusions. Thorough medical screening of organs and blood makes these unusual occurrences.

How Is Toxoplasmosis Diagnosed in Cats?

While T. gondii infection in cats is common, the toxoplasmosis disease is not, and Cohn notes that diagnosing the disease isn’t always easy. In an ideal situation, she’d be able to take a sample of tissue or fluid from the cat, put it under the microscope, and spot the toxoplasma organisms that way. That’s difficult to do because we don’t always know which tissues have been affected—and thus which tissues to test. More often, veterinarians are able to make a diagnosis by testing for antibodies to the parasite. Antibodies are produced by the cat only in response to a toxoplasma infection. This is a simple blood test that can be done in almost any veterinary hospital. 

How Can You Treat Toxoplasmosis in Cats?

Cohn says that some antimicrobial drugs can be used to treat the signs of toxoplasmosis, but recovery depends on which tissues are affected by the disease. For example, if toxoplasmosis has caused serious damage in the brain, killing the parasite may not be enough to save the cat. But if the disease is just in the eyes, even if the cat loses their sight, they can still live a long and happy life. So, prognosis is guarded. “Cats can absolutely recover, but I would never say they’re cured because they’re still going to have that parasite tucked away in their tissues forever,” Cohn says. 

Here’s How to Help Prevent Toxoplasmosis in Cats

According to Cohn, the best way to prevent your cat from developing toxoplasmosis is to prevent hunting so they’re less likely to pick up the parasite in the first place. While indoor cats can certainly catch and eat mice in the home, their odds of becoming infected are much lower than cats allowed to roam freely outside. And because Toxoplasma gondii can be found in other types of animals—including animals who are raised for food—she cautions against feeding cats raw meat of any kind.

Proper general wellness care for your cat can also help prevent illness due to toxoplasmosis by keeping their immune systems strong in case of exposure to T. gondii oocysts. This includes keeping them up-to-date with their vaccinations, having regular checkups, and blood tests as suggested by your veterinarian.