Is There Really a Parasite That Makes You Like Cats?

Cats are easy to love, but maybe you’ve heard that they can pass on a parasite that makes you like cats. As is often the case, there’s a grain of truth to the rumors, but the story is a lot more complicated. 

Here’s what science has to say about Toxoplasma gondii and what it actually does to the brain. 

What Is Toxoplasma Gondii in Cats?

Toxoplasma gondii is a microscopic, single-celled parasite that can infect most species of warm-blooded animals. It has a complicated life cycle, and cats—both wild and domestic—play an essential part.

Cats usually get infected with Toxoplasma by eating animals like rodents or birds that have cysts containing a dormant form of the parasite in their tissues. Toxoplasmosis in healthy cats is usually not a serious disease, but the parasites that have spread throughout the body eventually return to the cat’s intestinal tract where they produce oocysts (tiny egg-like structures).

Cats are the only animals that can shed the parasite’s oocysts in their feces, making felines essential for the parasite’s life cycle. When other animals inadvertently eat those oocysts, the parasites mature and eventually form cysts in their host’s brain, muscles, and other tissues. The cysts remain throughout the host’s life and bring the parasite’s life cycle full circle.

Toxoplasma Gondii's Effect on Rodents

Toxoplasma’s “goal” is to end up inside a cat so it can reproduce, and it has found fascinating ways to increase the chances of that happening.  

In a groundbreaking study, researchers found that Toxoplasma cysts in a rat’s brain altered the rat’s behavior in ways that made it more likely that it would be eaten by a cat. Infected rats seemed to become less fearful and would spend more time in areas that smelled of cat pee than uninfected rats. 

Additional research revealed that the parasite increases dopamine levels in the rodent’s brain, alters the amygdala (a brain region that processes fear), and produces other brain changes that can make rodents less cautious around cats. This has been called the “fatal attraction” effect. 

Does Toxoplasma Gondii Make Humans Love Cats?

There is no scientific proof that humans infected with Toxoplasma gondii love cats more than humans who aren’t infected.  

One study did find a possible, subtle version of the “fatal attraction” effect in people. When researchers asked men and women to rate the smell of diluted cat urine, Toxoplasma-infected men rated the odor as more pleasant than men who were not infected. In women, however, the opposite was true. 

But this research had mixed results and certainly didn’t prove that Toxoplasma makes people love cats.   

Is Toxoplasma Gondii Harmful to Humans?

For most healthy people, contracting toxoplasmosis causes few, if any, symptoms. It’s estimated that around one-third of people worldwide are infected with the parasite, and most never know it.  

When symptoms do appear during the initial infection, they tend to be mild and flu-like: swollen lymph nodes, muscle aches, and fatigue.

But there are important exceptions.

• If a person is infected for the first time while they are pregnant, the parasite can cause birth defects and miscarriages. This is why pregnant people are typically advised to avoid cleaning litter boxes. If that’s not an option, they should wear gloves and wash their hands thoroughly afterward.

• Toxoplasmosis can be a serious or even life-threatening disease for people who are immunocompromised. Parasites in cysts can become active and damage the brain, eyes, lungs, and other organs.

• Toxoplasmosis has also been associated with changes in human behavior, including increased risk-taking and novelty-seeking, as well as mental health conditions such as schizophrenia. However, a cause-effect relationship has not been proven.

But you don’t have to panic about your cat giving you Toxoplasma because: 

• You’re more likely to be infected with Toxoplasma by eating undercooked meat and unwashed produce, or through direct contact with contaminated soil (for example, while gardening). 

• Cats only shed oocysts in their feces for a few weeks and only after their first infection. 

• If you keep your cat indoors, there’s a low chance of them catching and eating infected prey. 

• Not feeding cats raw meat eliminates another route of transmission. 

• Oocysts can only infect humans once they’ve been outside of a cat’s body for one to five days, which is a great incentive to scoop your cat’s litter box daily. 

• Once a person is infected with Toxoplasma gondii, they generally develop immunity that protects against reinfection. 

So, keep loving your cat and know that your relationship is built on good care and true affection, not Toxoplasma.