Sam Ballard was 19 years old when friends at a party dared him to swallow a slug. Within days, the Australian teen developed a rare form of meningitis and fell into a coma that lasted more than a year. Even after waking up, he remains paralyzed from the neck down.

The culprit, doctors said, was a parasite in the slug called a rat lungworm, which can burrow into the human brain.

Ballard isn’t alone, or even the only person infected on a dare—at least three reported cases involve boys or young men who were dared to eat a slug or snail. What’s more, the parasite is now spreading to new places around the globe.

Originally from Asia, rat lungworm is