RFK Jr. says doctors found a dead worm in his brain. Here’s how it happens and why it’s rare in the United States

Independent presidential candidate Robert F. Kennedy Jr. says he lives with a dead worm in his brain, according to court documents obtained by The New York Times. Kennedy, 70, said the parasite’s remains were discovered in 2010 after he visited a neurologist about memory loss and brain fog, fearing he might develop brain cancer like his late uncle, Sen. Edward M. Kennedy. In a 2012 deposition, he claimed that what initially appeared to be a tumor was “caused by a worm that entered my brain, ate part of it and then died.” Kennedy suspects he caught the parasite during a trip to South Asia. Speaking to the NY Times, he said he no longer experienced any memory loss or dizziness related to the health incident, which he noted did not require treatment.

How can something like that happen? Here’s what you should know about the condition known as neurocysticercosis.

How does a worm get into the brain?

Kennedy’s disease can develop if you accidentally eat or drink the larvae of parasites. However, in the vast majority of cases it is caused by a specific type of tapeworm known by its scientific name Taenia solium, Dr. Michael Wilson, a neurologist specializing in infectious diseases at the University of California, San Francisco, tells Yahoo Life.

“Here’s how it can happen: A person becomes infected with a tapeworm by eating contaminated meat like pork,” William Sullivan, a professor of pharmacology, toxicology, microbiology and immunology at Indiana University School of Medicine, tells Yahoo Life. “The tapeworm produces tens of thousands of eggs in its intestines, which are then excreted in the feces. If you don’t make sure to wash your hands after using the toilet, you can become infected with the tapeworm eggs.”

Or the infected person’s dirty hands can contaminate food or water with tapeworm eggs. “In each case, the small tapeworms (larvae) that hatch from the eggs are tiny enough to break through the intestinal wall and form cysts in other organs, including the brain,” says Sullivan.

What are the symptoms?

“Once the tapeworm reaches the brain, it forms a cyst” — or fluid-filled sac — “in the brain tissue and just sits there,” Wilson says. “It can stay there for many years and not cause any clinical symptoms, and we don’t really understand why.” But at some point, “the immune system will say, ‘Hey, wait a minute,’ and attack it,” he explains.

The brain inflammation caused by the immune system’s attacks results in symptoms — by far the most common of which is a seizure — and is not caused by the worm itself, Wilson says. Worm larvae “sit in the brain, but it’s not like they chew their way through,” he adds.

A seizure is almost always the symptom that leads to the discovery of an active neurocysticercosis infection, but depending on the location and number of larval cysts, other effects such as speech or cognitive impairment are also possible. However, if a patient were struggling with memory loss, they would likely look for a different explanation, says Wilson.

How often does this happen?

Neurocysticercosis is rare in the United States. The Centers for Disease Control and Prevention (CDC) estimates that there are about 1,000 new hospitalizations due to the infection each year. But worldwide it is a big problem. The World Health Organization (WHO) estimates that tapeworms are responsible for about 30% of epilepsy cases in “endemic areas where people and roaming pigs live in close proximity.” People living in poorer countries and with less access to clean running water are at greater risk. If pork is stored at safe temperatures, cooked thoroughly, and good hand hygiene is maintained, infection becomes very rare.

Neurocysticercosis is not a common motion sickness, Wilson says. “Given the amount of Americans traveling to these parts of the world, it is very rare for people to come home and be at risk for this type of infection since they typically have access to clean water abroad,” he notes firmly.

How is it treated?

Treatment depends on when the infection is discovered and where the cysts are located in the brain. In extremely rare cases, Wilson says, a worm cyst can block the flow of cerebrospinal fluid and cause life-threatening brain swelling. In this case, the worm must be removed surgically.

If the worm is in its “active phase,” meaning the inflammation from the immune system’s attacks has not killed it, it is treated with antiparasitic medications, according to the CDC. But often – and as Kennedy’s description suggests, this was the case with him too – the worm is only discovered in the calcification stage. “Once the immune system destroys it, it just leaves this calcification, this little scar” in the brain, Wilson says. Typically, a few weeks or months can pass between an attack and the worm being killed and calcified. At this point there should be no further complications and there is nothing more doctors can do.