Editor’s note: This post was originally published on May 9 and has been updated.

“A worm…got into my brain and ate part of it and then died.”

These are words no one wants to say.

They came from a US presidential candidate and President-elect Donald Trump’s nominee to lead the Department of Health and Human Services. According to a 2012 deposition discovered and reviewed by The New York Times in May, Robert F. Kennedy Jr. said he sought medical attention after experiencing mental fog and memory loss. Eventually, he said, a doctor helped him determine that a brain abnormality found on a scan was caused by a worm. He says now The Times he recovered without long-term consequences.

The story created a lot of buzz in the world of politics. But it’s not just a story about a politician’s health history. The World Health Organization it is estimated that over one billion people are infected with parasitic worms. The implications are often serious and lifelong.

NPR spoke with Francesca Mutapiglobal professor of infection and immunity at the University of Edinburgh, who has studied parasites for 25 years. She shared her knowledge of what might have happened to RFK Jr. – and the tolls that parasitic worms take on the world. The conversation has been edited for length and clarity.

Let’s start with RFK Jr. What we know about his particular case is vague. Do you have a hunch about what this worm could have been and how it could have been infected with it?

So I have absolutely no idea about his case. From what I’ve read, it may have been a certain infection known as taeniasis. And taeniasis is an infection you get from a tropical parasitic worm – the easy name is tapeworm (which can be carried by pigs).

What happens is when you get infected with a tapeworm, usually from raw pork or undercooked pork, you ingest the eggs and those eggs will continue to hatch. And in their larval form, they will spread throughout the body and, depending on the tissues in the body they reach, cause a disease called cysticercosis.

Where might these larvae travel in the body and what harm can they do?

For example, if the larvae get into the eyes, they can cause blurred vision and blindness. If they get into the muscles, they can cause weak muscles. But if they reach any part of the central nervous system – the spine or the brain – then they cause a form of disease called neurocysticercosis.

And this particular form of the disease will vary depending on your immune system and your health and where exactly those larvae came from. It can cause headaches and convulsions. For example, the disease is the leading preventable cause of epilepsy worldwide. It can also cause problems with cognition. And some people have problems with balance problems, lack of attention and also confusion. Excess fluid in the brain can make it a very dangerous condition. And in very, very rare cases, people actually die from neurocysticercosis.

How likely is this in an American context?

What tends to happen is that you are exposed to parasites when you travel to areas where this disease is prevalent. So Asia, for example, South America and in some parts of Africa. In the United States, according to Centers for Disease Control and Preventionyou have about 1,000 new cysticercosis hospitalizations each year.

What are the treatment options?

Well, for one, these diseases can be prevented with things like good food hygiene – making sure pork is well cooked – good hand washing and good sanitation of course.

But if you fail to prevent (the disease), then it is treatable and the drugs work very well. Two widely used drugs that kill the larval stages are praziquantel and albendazole. They are usually good for two things: they can reduce or kill the parasites and they can also reverse some of the pathological manifestations of the disease, such as inflammation. In extreme cases, you need to have surgery.

Tell us more about the global burden of parasites and worms in particular?

Diseases caused by parasitic worms are mostly part of a group of diseases called neglected tropical diseases, and about 1.7 billion people are affected by NTDs.

In Africa alone, for example, we have over 200 million people who are affected by bilharzia, a disease caused by parasitic worms (which can trigger a range of health problems from anemia to blood in the urine to cognitive problems).

So it’s a huge burden. If you took all the children in the world who have bilharzia and made them hold hands, they would go around the world one and a half times. This is the burden of one of the 21 neglected tropical diseases.

Although we have few deaths (due to diseases caused by parasitic worms), what we do have is a huge impact on our overall day-to-day health and ability to function.

So can you talk about the consequences of cysticercosis – or other parasitic worms?

Think of an epileptic fit. You cannot hold down a job easily or for long if you have epileptic seizures. If (the worm gets to your eye and) it affects your vision, it affects the jobs you can do and your safety. If you have problems with balance, it is difficult for you to move around. So that the quality of life is really reduced.

Similarly, bilharzia in my mother tongue – the Shona of Zimbabwe – is called a disease of cognitive function. Some of the classic symptoms are children who are tired, have poor memory and poor cognition. One of the big improvements we see whenever we treat children and catch the disease early is that their school performance increases as well as their physical activity.

What is being done to combat this globally – and is it enough?

A lot is done, but a lot can be done. We have what we call preemptive chemotherapy, which is the treatment of populations at risk of the disease – you give them the drugs and they catch the infection before it causes serious disease. These drugs are mostly donated by international pharmaceutical companies.

Now we need to accelerate these efforts so that we can try to eliminate these types of diseases as quickly as possible. We can do this by increasing treatments. But we can do this by being even more innovative in our interventions. We can develop vaccines, for example.

Spokesman for RFK Jr. said he contracted the parasite while traveling to places in Africa, South America and Asia in his role as an “environmental advocate”. Is there anything people can do to protect themselves in these parts of the world?

In areas where we have cysticercosis, you can improve hygiene so that people do not come into contact with faeces or pig urine. This type of intervention is very, very cheap, but very, very effective.

And as you note, even though RFK JR. the story is a bit…unusual…it provides an opportunity to talk about the global problem of parasitic worms.

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