Last week, Australian Sam Ballard died after an eight-year illness that all started with an unexpected assailant: a garden slug he swallowed on a dare.

As a 19-year-old in 2010, the rugby player attended a small gathering with a few friends, where they encouraged him to swallow a live slug. This feat may have been harmless — if a bit gross — except that the slug contained a hidden parasite: a nematode called Angiostrongylus cantonensis, commonly known as rat lungworm.

Shortly after swallowing the slug, Ballard became paralyzed. He experienced brain damage and never fully recovered. He died at age 28 on Friday.

Despite Ballard’s untimely death, he was fortunate to receive medical care that helped give him a few more years with his family and friends. Many animals that encounter A. cantonensis aren’t as fortunate, as in the case of the tawny frogmouth (Podargus strigoides) in the video above. ☝

This Australian bird probably became infected in the same way Ballard did: By eating an infected mollusk like a slug or a snail. As the video shows, the infected bird is mostly paralyzed and has trouble breathing. But if it got infected by eating a snail, then why is the disease called rat lungworm disease? It all has to do with the parasite’s strange life cycle.

The US Centers for Disease Control and Prevention video above shows that A. cantonensis infects the lungs of a rat, usually living in the pulmonary artery, the blood vessel that carries blood from the heart to the lungs. Eventually, the worms are simply in the rat’s lungs, at which point the hapless animal coughs them up. And instead of spitting the worms out — as that would be quite rude — the rat swallows the worms. As most of us know, what is swallowed eventually gets pooped out, and this is how the rat lungworms can infect other animals.

When a slug or snail slimes over an infected rat’s poop, it either eats the worms or becomes an unwitting carrier as the worms penetrate its body. Then, when a rat eats the infected mollusk, the whole process begins again. Sometimes, though, as in Ballard’s case or in the tawny frogmouth’s case, a non-rat animal will fall victim to the nasty parasite.

The Tawny Frogmouth bird
The Tawny Frogmouth.

And even though it may sound farfetched, Ballard isn’t alone. Around the world, people become infected by the rat lungworm by accidentally eating fruits or vegetables that haven’t been properly washed. They can contain worms left behind by slugs or snails, or they can contain the mollusks themselves. In one case, reports the CDC, a boy in New Orleans became sick with suspected rat lungworm disease when he ate a snail on a dare in 1993. Despite showing some initial symptoms, his illness went away in two weeks without treatment.

In a 2016 paper published in the journal Parasitology, a team of researchers outlined findings from examining a handful of tawny frogmouths, as well as some small Australian mammals that had contracted the disease. They write that a diagnosis is usually made based on symptoms and “history of mollusc consumption,” as well as test results on cerebral spinal fluid. The reason for this last one is that rat lungworm disease can cause eosinophilic meningitis, a condition with a range of symptoms including coma and death. In Ballard’s case, doctors made his diagnosis quite quickly once he told them he’d eaten the slug. By then, it was too late, though.

For the most part, this rare disease is not a cause for concern. If a person becomes infected, they can’t infect another person. The CDC recommends avoiding rat lungworm disease by washing vegetables well under running water, as well as thoroughly cooking any freshwater crabs, shrimp, or frogs before eating them since these animals could eat infected slugs and snails.