RFK Jr. says a parasite ate part of his brain. How common are they?

Presidential candidate Robert F. Kennedy Jr. turned heads Wednesday when the New York Times reported on a 2012 deposition, in which he said doctors had found an abnormality on his brain in 2010 that he said was “caused by a worm that got into my brain and ate a portion of it and then died.” The brain scan was ordered by physicians after he experienced memory loss and mental fogginess. Friends worried he might have a brain tumor, which had claimed his uncle, Senator Edward Kennedy, the year before. (RFK Jr. says he recovered from the symptoms and has had no lingering aftereffects.) Political ramifications of this deposition aside, it has gotten people more than a little curious about brain parasites. Here’s what you need to know—though you might not want to read this as you enjoy a snack. Are brain parasites real? Yes, despite sounding like something out of a science fiction film, brain parasites are very real—and more widespread than you might imagine. The Centers for Disease Control and Prevention (CDC) says an estimated 11% of the U.S. population, 6 years and older, has been infected with toxoplasmosis, an infection caused by a parasite called Toxoplasma gondii, which infects your brain. Globally, that number is as high as 60%. “Infection is often highest in areas of the world that have hot, humid climates and lower altitudes,” the CDC writes. It’s not just humans, Toxoplasma also gets into the brains of everything from birds to whales. And the parasite can only reproduce in a cat’s gut. Toxoplasmosis is the most common parasite, but the National Institute of Health (NIH) says cerebral malaria, neurocysticercosis, and neuroschistosomiasis are other parasite-driven infections of the nervous system. Some tapeworms can travel from your gut to your brain, though that’s rare. And if you want to get especially gross, there’s Naegleria fowleri, aka the “brain eating amoeba,” which lives in soil and warm fresh water, such as lakes, rivers, and hot springs. That one can cause a brain infection when water containing it goes up a person’s nose. (Look, we warned you not to read this while you were eating.) Can parasites eat your brain? That’s unlikely, say experts. Although it’s impossible for us to know for sure whether a worm ate part of Kennedy’s brain, many experts have noted that tapeworms can live on the nutrients in the brain but don’t generally eat brain tissue. What causes brain parasites? Often, when people contract parasites, they stay limited to the digestive system, but sometimes they can travel from the gut into the bloodstream and through the blood-brain barrier. Transmission largely comes in one of three ways: Humans can become infected via foodborne transmission, specifically by eating undercooked or contaminated meat, such as pork, lamb, or venison. Shellfish, like oysters and mussels, can also pass it along. In addition, knives that cut contaminated food can spread the parasites to other food items if not cleaned thoroughly. Animal-to-human transmission can also occur, most frequently through a cat’s feces, in the case of toxoplasmosis. If the feline contracts the parasite, it can infect humans when the litter box is cleaned. (As if you needed additional admonishment, but, wash your hands, folks!) Pregnant mothers can also pass an infection to unborn children, and there are rare cases of transmission via organ transplants. What are the symptoms of a brain parasite? Most people who are infected will never know it and never show symptoms. Those who do become symptomatic report everything from a fever, muscle aches, and a headache to swollen lymph nodes and a skin rash. Confusion, coordination issues, and changes in alertness can also present as symptoms, says the Mayo Clinic. For a brain tapeworm, symptoms often depend on where cysts form, but headaches and seizures are the most common. The CDC says a brain tapeworm is a “leading cause of adult onset epilepsy.”  What long-term effects do brain parasites cause? Most healthy people recover from parasites like toxoplasmosis without treatment and don’t show any long-term effects. In rare cases, though, there have been observed behavioral changes, including anxiety, depression, and hyperactivity. One 2013 study is much more alarming, though, suggesting that for people with immune deficiencies, toxoplasmosis might be indirectly responsible for everything from traffic accidents to suicides—even a possible cause for schizophrenia. Can brain parasites kill you? Technically, yes, but the odds of it happening are considerably low. In a 2019 study, toxoplasmosis deaths made up less than one-tenth of a percent of the total deaths recorded in 37 hospitals studied by researchers, being attributed to just 188 out of 247,976.  As for brain tapeworms, technically known as neurocysticercosis, those are responsible for an estimated 1,000 hospitalizations per year, says the CDC. Cases are most frequently