Cat owners know the joy the company of their feline friends can bring, but beneath those cute whiskers and button noses is an unwelcome houseguest with a nefarious mission. Toxoplasma gondii, commonly referred to simply as toxo, is a parasite carried by felines that can cause a disease called toxoplasmosis in humans. The parasite, which can be transmitted to cat owners through the animal’s feces, can give rise to a host of health issues, including putting some people at greater risk of developing schizophrenia, according to the latest study to look at the effects of the parasite on cat owners.

“Cat ownership in childhood has now been reported in three studies to be significantly more common in families in which the child is later diagnosed with schizophrenia or another serious mental illness,” researchers said of the new study, published this month in the journal Schizophrenia Research. While not the first study to link T. gondii to mental illness, the new research puts a fresh spotlight on the risk the parasite can pose to cat owners. Since 1953, 19 studies have shown some link between psychiatric disorders and T. gondii, according to Pioneer News.

Here are five things to know about the T. gondii and toxoplasmosis. 

1. T. gondii is the most common parasite in developed countries. Some 60 million Americans are believed to carry the parasite; however, most do not exhibit symptoms of toxoplasmosis, CBS News reported.

2. Humans are more likely to get the parasite from gardening or eating uncooked meat than directly from their pets. According to the U.S. Centers for Disease Control and Prevention, accidentally ingesting soil or food contaminated with cat feces is the most common way the parasite is passed to humans.

3. Severe toxoplasmosis can cause damage to the brain, eyes or other human organs. Such effects are most common in people with weakened immune systems, the CDC reports.

4. Cats contract the parasite from rodents. Research has shown that rodents infected with T. gondii lose their natural fear of cats. Once the parasite finds a feline host, it reproduces.

5. Treatment for toxoplasmosis is not always necessary. Most symptoms subside within a few weeks to months. However, there are medications to treat the disease.