The strange and tragic death of a 29-year-old Australian man last week has underscored the seriousness of a rare parasitic infection called “rat lungworm disease.”

Sam Ballard of Sydney was at a party in 2010 when he ate a slug on a dare.

“We were sitting over here having a bit of a red wine appreciation night, trying to act as grown up and a slug came crawling across here,” Ballard’s friend Jimmy Galvin told Australian news. “The conversation came up, you know. ‘Should I eat it?’ And off Sam went. Bang. That’s how it happened.”

Days later, Ballard complained of leg pain, and was eventually diagnosed by his doctor with a rat lungworm infection.

The parasite Angiostrongylus cantonensis is harbored by rats and can be passed to snails and slugs, who in turn can transmit the worm to humans. Once ingested, the worm can penetrate the intestine, traverse the nervous system, and burrow into the brain’s outer lining.

Most people will recover on their own from the infection, according to the Centers for Disease Control and Prevention (CDC), but it can also cause an uncommon form of meningitis, and manifest as a “headache, stiff neck, tingling or painful feelings in the skin, low-grade fever, nausea, and vomiting.”

Ballard developed this type of meningitis, called eosinophilic meningoencephalitis, which put him in a coma for 420 days. When he awoke, Ballard was left with brain damage, at first unable to move his limbs. He regained some movement, but became quadriplegic, experienced seizures, and required permanent care which was facilitated by his mother Katie Ballard.

“His friends have stuck by him ever since,” Australian journalist Lisa Wilkinson said last week, reporting Ballard’s death. “On Friday, Sam passed away, surrounded by his family and loyal, loving mates.”

“His last words to his mum: ‘I love you.’”

Ballard’s unfortunate case is an outlier, but recent rat lungworm outbreaks have generated newfound awareness about the tiny parasite.

Rat lungworm has spread to more than 30 countries including the US. There have been at least 2,800 cases of infection worldwide. It caused a panic in Hawaii last year when dozens of cases were documented statewide. (On average, the islands report one to nine infections each year, with two related deaths since 2007, according to the Hawaii Department of Health.)

The transmission process of rat lungworm disease. Image: Hawaii Department of Health

Transmission begins when a rat coughs up the worm’s larvae, and swallows them into its stomach. The larvae are then passed through the rat’s digestive system, and out through its poop. Slugs or snails serve as intermediate hosts by eating the rat’s poop and contracting the parasite.

When a rat eats one of these infected gastropods, the worm’s lifecycle is renewed. The larvae will mature into two millimeter-long adults within the rat’s brain, before traveling to its lungs via the pulmonary arteries and eventually breeding there.

Humans and other animals can become sick if they eat an infected slug or snail. (People who deliberately consume gastropods are urged to not eat raw or undercooked ones.) Accidental infection can occur from unwashed produce that contains an infected slug or snail, or even their slime, according to Australian health officials. Less commonly, infected crabs, shrimp, and frogs can also transmit the parasite, as well as contaminated drinking water.

“The parasites are in the lining of my brain, moving around,” an infected Hawaii woman told local news site Civil Beat. “My visual graphic for what’s happening is that every once in a while somebody opens the top of my head, sets a hot iron inside my brain, then pushes the steam button.”

Doctors sometimes perform a spinal tap to detect the disease. There is currently no rat lungworm test, and attempts to create a test for antibodies associated with the infection have proven divisive.