The Dangerous Parasite Lurking in Cat Litter

If you or someone you love were pregnant in the last several decades, you probably were warned to avoid changing the cat litter tray. That's because cat feces often contain the tiny Toxoplasma gondii parasite, which can cause severe problems in fetuses if a woman contracts it during or just before pregnancy. Expectant mothers may rejoice in the nine-month reprieve from kitty litter duty, but there’s a decent chance you or someone you love already harbors the parasite: Toxoplasmosis, the disease that results from the Toxoplasma gondii parasite, infects about 30 percent of people in the U.S., and even more in some other countries.

Here's what you should know about this common parasite.

1. Who Gets Toxoplasmosis, and How Is it Transmitted?

Anybody can contract toxoplasmosis, at any time. "It’s probably one of the most common infections on the planet," says toxoplasmosis expert Emma Wilson, PhD, associate professor in the school of medicine at the University of California, Riverside. Coming into contact with cat feces is one way to contract it, but according to Wilson it’s much more common to ingest the parasite: "We eat it in meat that hasn’t been properly cooked," she says, citing too-raw lamb as a prime culprit.

But the U.S. is far behind some other countries when it comes to rates of toxoplasmosis: Meat-loving nations such as Brazil and France feature an infection rate of about 80 percent. Other methods of transmission, according to Wilson, include drinking water or eating unwashed fruits and vegetables contaminated with the parasite, or using contaminated utensils.

2. Is Toxoplasmosis Dangerous?

In the average person, the parasite is benign. Chances are you’ll never even know you have it.

However, infection can be a problem in people who are immunocompromised in some way. It's estimated that at least 10 million Americans are immunocompromised due to organ transplants, cancer treatment, or HIV/AIDS. (This doesn't account for people with autoimmune disorders and other conditions that can affect the immune system.)

An immune system that’s not functioning properly can cause a latent Toxoplasma parasite to "switch on" and cause damage. In immunocompromised people, toxoplasmosis can cause blurry vision and eye infections. It can affect brain cells, causing neurological difficulties and even psychiatric issues. The parasite has been linked to diseases such as Alzheimer’s, Parkinson’s, schizophrenia, and epilepsy, and can affect a multitude of major organs. It can be so destructive that, if untreated, it can kill.

Researchers are also realizing that the disease may be more nuanced than originally thought. Rather than being either completely destructive or completely dormant, there are likely to be shades of gray when it comes to the problems that toxoplasmosis causes.

"[Symptoms] probably [have] a lot to do with the degree of infection in the brain and other genetic factors," says Wilson. Even a small amount of the parasite "may lead to slight changes in [brain] function that are not considered pathological [clinically significant] but may ultimately trigger changes in behavior or even other neurological disease."

What does this mean? Well, several studies have found a link between drivers infected with the toxoplasma parasite and an involvement in vehicular accidents, Wilson says. "More and more studies are suggesting that even though we consider toxoplasmosis quiet and latent [inactive] in the brain, it’s not that quiet."

3. Who Gets Tested?

Anyone who donates or receives an organ transplant in the U.S. is automatically tested for toxoplasmosis; blood is drawn and examined to determine if you're producing antibodies to the parasite.

If you're immunocompromised for other reasons, you'd probably be tested only if you have symptoms of a significant neurological disorder such as sudden-onset seizures or the inability to walk.

4. How Is Toxoplasmosis Treated?

Treatment usually involves a regimen of pyrimethamine, an antimalarial medication, along with sulfadiazine, an antibiotic. "If you are immunocompromised, they are taken for as long as you remain immunocompromised," says Wilson. If you're taking the meds because you and your doctor believe you may have recently contracted the parasite (for instance, if you work in a lab and inadvertently jabbed yourself with a contaminated needle), the usual course is two to six weeks. The drugs are not advised for pregnant women.

5. How Can I Avoid Getting the Disease?

Unfortunately, there’s no vaccine to prevent toxoplasmosis. To be safe, the Centers for Disease Control and Prevention (CDC) suggests that you:

  • Cook Food Thoroughly
    Use a food thermometer to ensure that poultry is heated to 165 degrees Fahrenheit, ground meat is heated to 160 degrees Fahrenheit, and whole cuts of meat are heated to 145 degrees Fahrenheit. Except for ground meat, these foods also require a rest period of three minutes before consumption, which allows for additional pathogens to be eradicated.
  • Practice Food Safety
    The CDC also recommends peeling or washing produce before eating; avoiding raw seafood; staying away from unpasteurized goat’s milk, and thoroughly washing utensils and cutting boards.
  • Change Your Cat's Litter Daily
    Keeping cats as pets is not a problem as long as you’re vigilant about cleaning out the litter box on a daily basis--the parasite cannot infect you for at least one and up to five days after it’s shed in the feces. (This does not apply if you’re pregnant, in which case you definitely should avoid the litter box.) You also can lower the risk of your cats contracting the parasite by keeping them indoors and feeding them commercially manufactured cat food.
  • Wear Gloves When Gardening or Handling Soil
    Soil can contain cat feces.

Emma Wilson, PhD, reviewed this article.


Wilson, Emma, PhD. Phone call with author on May 11, 2016.

"Toxoplasmosis Frequently Asked Questions (FAQs)." Centers for Disease Control and Prevention. Last reviewed January 10, 2013.

"Epidemiology & Risk Factors." Centers for Disease Control and Prevention. Last reviewed December 14, 2015.

"Prevention & Control." Centers for Disease Control and Prevention. Last reviewed December 14, 2015.

"Toxoplasmosis—Symptoms." Mayo Clinic. Last updated July 24, 2014.

"Toxoplasmosis—Treatments and Drugs." Mayo Clinic. Last updated July 24, 2014.

"Toxoplasmosis—Tests and Diagnosis." Mayo Clinic. Last updated July 24, 2014.

Schall, Theo. "How many Americans Are Immunocompromised?" Johns Hopkins Berman Institute of Bioethics/Berman Institute Bioethics Bulletin. February 11, 2015.