Food for Thought: How and Why Tapeworms Find Their Way Into Your Brain

When independent candidate for president Robert F. Kennedy Jr. announced last week that doctors had found a dead parasite in his brain over 10 years ago, we reached out to Biology Professor Scott Villa. 

Villa will teach a “Parasites and Pathogens” course this fall and studies the effects of parasites on monarch butterflies, among other topics.

It is unconfirmed but the consensus seems to be that Kennedy Jr. had contracted a pork tapeworm. A New York Times story quoted Kennedy saying that a doctor believed the worm had gotten into his brain and eaten a part of it. Do pork tapeworms actually feed on your brain?

Kennedy could have suffered from a condition known as neurocysticercosis, when tapeworm larvae get into your circulatory system and make it into your brain. There, they can burrow into brain tissue and form what’s called a cyst, which is just a protective capsule that allows the parasite to evade the immune system. 

The fact that they form cysts in the brain is a rather fine distinction: They burrow into brain tissue and can hang out there for a long time but they are not actually feeding on the brain. 

What happens to the host in that case?

It varies because it depends on where the cysts form. People can live asymptomatically with cysts if the parasites aren’t affecting the parts of your brain that control movement or speech. It's like any parasitic infection, the more cysts you have the worse it is.

Tapeworms are most common in places without high standards of sanitation, right? 

First, this tapeworm is more common in places that eat a lot of pork. And people in the U.S. do eat a lot of pork. So, while extremely rare, it’s possible to contract this type of tapeworm from eating undercooked pork from an infected pig. It’s more prevalent in underdeveloped countries or areas with poor sanitation protocols. 

Are there other parasites that can affect the brain like this? 

There are other parasites that affect the brain but the most common are members of the class of parasites called “cestodes,” which are more commonly known as tapeworms. 

Different tapeworm species may cause different pathologies but generally all follow the same route: A mature tapeworm lodged in their host’s intestinal tract starts to produce thousands of eggs that get flushed out through feces into the environment. They are transmitted when pigs ingest the eggs through dirty water or sewage. Then, the eggs hatch into larval stages which can enter your circulatory system and they find muscle, brain, liver, and other organ tissue to develop into cysts. Striated muscle tissue is the most common landing spot for these larvae – and that’s how humans often contract it by eating undercooked pork.

What’s interesting is that the actual mature tapeworms in your intestines don’t really hurt you. The larval stages are the ones that cause problems.

Why would a tapeworm be attracted to brain tissue?

It's relatively unknown what mechanisms parasites use to find certain host tissues. Certainly there is a bit of chance at play. Again, a vast majority of larval tapeworms settle into muscle or the intestines. But, from an evolutionary standpoint, sitting in the brain might be adaptive for increased transmission in some cases. In the wild, predators will often eat the brains of their prey first and if the prey was a host of a tapeworm, the tapeworm will be ingested by the predator. But the jury is still out on the efficacy of these transmission dynamics.