On November 2, 2018, Sam Ballard was killed by something he ate in 2010.
The Australian had swallowed a live slug on a dare back then. All these years later, he was diagnosed with an infection of rat lungworm, a parasite the slug had evidently been carrying. The infection caused eosinophilic meningoencephalitis, a rare kind of meningitis. As a result, Ballard fell into a coma for more than a year, endured a severe brain infection, and ended up paralyzed from the neck down.
Although Ballard survived for eight years after the initial infection, symptoms apparently developed quickly. According to a LiveScience report, a few days after swallowing the slug, Ballard began complaining of leg pains, became dizzy, and started vomiting. It would've been entirely possible for the infection to lie dormant all this time, though—some parasites and bacteria can camp out undetected for years. Take H. pylori, an infection that could be affecting half the stomachs in the world at this very moment, yet only some people will develop ulcers and other symptoms.
What lets an infection stay hidden for years? Part of it has to do with the bacteria or parasite in question and how it behaves. Whereas bacteria like E. coli will reproduce fast, a particularly slow-multiplying bacteria—like the one that causes leprosy—can take up to 20 years to build to a level where its stereotypical blisters and rashes will appear.
The health of the host is also a factor. Consider one of the big problems during the AIDS crisis: HIV takes a long time to infect enough immune cells to create visible symptoms; people infected with HIV often still presented as perfectly healthy, sometimes for ten years or more. Transmission would still be possible, but no one—including the host—would necessarily suspect they were sick. AIDS, the acute portion of the disease, acts much faster in part because the infected person's immune system is significantly weaker.
In some parasitical infections, if the infected person is healthy, the parasite will die off naturally, stymied by the host's immune system. In fact, that's what usually happens in human cases of rat lungworm. Other common parasitical infections like giardia also tend to clear up within a few weeks, sometimes without any symptoms at all.
However, if all of that seems reassuring, you should know that in a few cases a dead parasite can actually be more trouble than a live one. Take tapeworm infections. They're generally limited to one or two symptomless adult tapeworms, which can live in the intestine for up to 30 years. In rare and severe cases, though, larval infections can migrate outside the intestine, even reaching the brain or central nervous system. The larvae seem to be able to secrete chemicals that keep them safe from the immune system; when they die, however, the immune system begins attacking, which can cause severe headaches, seizures, and paralysis.
There's a lot that doctors and scientists still don't understand about these infections. It's safe to say, though, that you're better off avoiding common carriers: raw meat, impure water, undercooked seafood. And, unfortunately, slugs.
Eleanor Hildebrandt is a writer/researcher from Seattle. She is the Factmaster for the Most Useful Podcast Ever.
