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CNN  — 

It was just a silly dare among teenage boys. What could it hurt to eat a small slug?

So Australian teenager Sam Ballard grabbed the slimy creature and gulped it down. He had no idea that the slug carried a potentially deadly worm that would put him into a coma that lasted more than a year, paralyze his body and ultimately take his life.

‘Trying to act like grown-ups’

In 2010, 19-year-old Sam, an avid rugby player, was drinking with Jimmy Galvin and several more of his Australian “mates” when a slug began crawling across Galvin’s concrete patio at his home in Sydney.

“We were sitting over here, having a bit of red wine appreciation night, trying to act as grown-ups,” Galvin recalled in a video interview this year with Lisa Wilkinson of “The Sunday Project,” a current affairs talk show that airs on Network 10 in Australia. CNN reached out to Galvin but has not heard back.

“And then the conversation came up, ‘Should I eat it?’ ” recalled Galvin. “And then off Sam went and bang, that’s how it happened.”

After downing the slug, Sam became weak and complained of severe pain in his legs, according to “The Sunday Project.” Sam’s mother, Katie Ballard, told the news show that at first they worried he might have multiple sclerosis, which had afflicted her husband. But doctors said no, that wasn’t the cause.

Then Sam turned to his mother and told her he had eaten a slug, “And I went, ‘No, no one gets sick from that,’ ” Katie Ballard said. CNN has also reached out to Ballard.

Soon, however, doctors told them otherwise. Sam had developed rat lungworm disease from the infected slug, changing his life forever.

Katie Ballard, left, with her son, Sam Ballard, in Sydney.

What is rat lungworm disease?

Rat lungworm disease is caused by a parasitic worm called Angiostronjilus cantonensis. As the name suggests, the parasite lodges in the lungs of rats and is later excreted in poop.

Along comes a slug, snail, freshwater crab, shrimp, prawn or frog, and either eats the rat dung or the parasite works its way into the creature infecting it. Fish, however, do not spread the parasite.

Humans can be infected if they eat the raw or undercooked contaminated animals, or vegetables carrying unseen snails or slugs that have not been thoroughly washed.

In addition, says the US Centers for Disease Control and Prevention, beverages can become contaminated with worms if left open for snails and slugs to enter.

Unlike in rats, the worm’s life cycle is not completed in a human. So instead of passing through the digestive tract, the worm larvae “can get lost, and it will go to the brain, and it’ll stay there,” said Heather Stockdale Walden, an assistant professor in the Department of Infectious Diseases and Pathology at the University of Florida. The parasite is not passed from human to human.

“When it gets to the brain, you can have eosinophilic meningitis,” Walden said, which is an inflammation of the membranes surrounding the brain and spinal cord.

Symptoms can include headaches, nausea, vomiting, fever and a stiff neck, the CDC said.

‘So full of love’

Most cases of rat lungworm disease are typically mild. But in some cases, like Sam’s, the disease can cause catastrophic damage.

Soon after the diagnosis, Sam fell into a coma, where he remained for 420 days, Ballard said in the Australian news report. He woke up paralyzed, unable to eat without a tube or move without intense effort. He required 24-hour care, seven days a week.

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But the disease didn’t affect his mental faculties, his family and friends said.

“He’s in there, 100%,” Galvin told “The Sunday Project.” “I apologized to Sam about everything that happened that night in the backyard. And he just started bawling his eyes out. I know he’s there.”

Late last week, Sam died, “The Sunday Project’s” Wilkinson wrote in a blog post.

“Sam passed away on Friday morning at Hornsby Hospital, not far from where he grew up, surrounded by 20 of those he most loved in the world,” she wrote.

“Katie tells me ‘the room was so full of love,’ ” Wilkinson said. “One of his friends there in the room continued, ‘He had his voice and he said “I love you” several times to Katie.’ “

A funeral service will be held for Sam on Thursday, according to a post on Galvin’s Facebook page.

CNN’s Susan Scutti contributed to this report.