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Presidential candidate Robert F. Kennedy Jr. said he suffered memory loss and severe brain fog more than a decade ago, potentially related to a parasite in his brain, according to the New York Times.
In a 2012 deposition reviewed by the Times, Kennedy said a worm “got into my brain and ate a portion of it and then died.” He said the cognitive issues later resolved. Around the same time, the Times reports, Kennedy was also diagnosed with mercury poisoning, which can also result in cognitive issues.
Though they sound like something straight out of a horror movie, parasites can and do affect the human brain. Here's what to know.
How do parasites get into the brain?
According to the Times' reporting, Kennedy said he did not know which type of parasite affected him, but experts told the Times it likely came from the larvae of a tapeworm sometimes found in pork. People can ingest a tapeworm’s eggs by eating contaminated food or water, resulting in the parasitic infection cysticercosis—which is called neurocysticercosis when it affects the brain.
Most often, people contract neurocysticercosis not directly from eating pork, but through exposure to fecal contamination, says Scott Gardner, curator of the Manter Laboratory of Parasitology at the University of Nebraska-Lincoln. If someone eats undercooked pork carrying a tapeworm, they may later pass the worm's eggs through their feces. If the affected person does not properly wash their hands after using the bathroom, they may spread the worm’s tiny eggs to household surfaces or to food and water, potentially leading people to ingest them and get sick, according to the U.S. Centers for Disease Control and Prevention (CDC). When the eggs hatch and larvae get into tissues like the brain, they form cysts there.
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Neurocysticercosis is rare in the U.S., but it is more common in parts of Asia and Latin America, says Gardner. As of 2017, the U.S. National Institute of Allergy and Infectious Diseases estimated that only about 1,500 cases were diagnosed in the U.S. each year. A 2012 study estimated its mortality rate to be around 0.06 deaths per 1 million people in the U.S.
Toxoplasma gondii is another far more common parasite that can affect the human brain, resulting in the infection toxoplasmosis. It can be spread via exposure to feline feces, as well as eating undercooked meat or shellfish or drinking contaminated water, the CDC says. The CDC estimates that up to 40 million people in the U.S. carry the parasite, though many don’t know it.
How dangerous are brain parasites?
Surprisingly, brain parasites don’t always cause serious issues, says Tajie Harris, an associate professor of neuroscience at the University of Virginia School of Medicine who has studied brain parasites. “We acquire a lot of infections that we never really notice or attribute to these viruses or parasites that do end up in our brains for the long-term,” she says. “Most of them go into this dormant state and cause us no problems in our lifetime.”
Harris’ research, for example, has shown that the brain launches such an effective immune response against T.gondii that many people never develop toxoplasmosis symptoms. When people do experience symptoms, which can be treated with antiparasitic medications in combination with antibiotics, they may develop flu-like muscle aches and swollen glands. Severe toxoplasmosis, which is most common among infants and people who are seriously immunocompromised, can result in damage to the brain, eyes, and other organs. Some studies have also linked the infection to mental-health issues, although Harris says that science is less settled.
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Neurocysticercosis can also remain dormant for some time. People do not typically develop symptoms until cysts caused by the parasite die, which can take months or even years, the CDC says. Symptoms can include headaches, seizures, confusion, and difficulty focusing and balancing. In serious cases, the condition can lead to excess fluid around the brain, which may be fatal. Typically, neurocysticercosis can be treated with antiparasitic drugs, sometimes used in combination with anti-inflammatory medications and surgery.
Dr. Michael Schulder, professor and vice chair of neurosurgery at Northwell Health in New York, says the symptoms Kennedy apparently suffered, including memory loss and brain fog, are not typical for neurocysticercosis and would likely be associated with a "particularly large cyst that put pressure on the brain."
The parasite also does not eat the brain, he clarifies. If it did, the sufferer would have permanent damage. "It may not be gross damage that would prevent you from leading an independent life," Schulder says, "but it would certainly prevent you from functioning at 100%."
How can I prevent brain parasites?
Good hygiene and food preparation practices are important. Health authorities emphasize the importance of thoroughly washing your hands after using the bathroom, changing a child’s diaper, or handling a cat’s litter box. And make sure to wash fresh produce and cook meat to a safe temperature, which for pork is at least 145°F.
But, Schulder says, the average person shouldn't spend much time worrying about parasitic brain infections—particularly not rare ones like neurocysticercosis. "In a society where public health and public hygiene measures are typically taken, and we have a Food and Drug Administration that oversees production of food and how it's made available to the public," he says, brain-invading parasites shouldn't be a major concern.
