John Carpenter's 1982 horror classic "The Thing" begins with a chase scene: Hunters pursue a lone dog across Antarctic wastes, seeking to exterminate the dreadful alien parasite that hides within its form. As the tagline states, man may indeed be "the warmest hiding place," but man's best friend will do in a pinch.
Fortunately, reality spares us the horrors of infectious, shape-shifting extraterrestrials, but humanity still has to contend with a host of parasitic organisms — and now the nematode Guinea worm (Dracunculus medinensis) has seemingly taken a page from The Thing's playbook, finding refuge within dogs to avoid total eradication.
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Typically, the Guinea worm life cycle plays out like this: Larvae infect tiny freshwater copepods, which then enter a human host through unfiltered drinking water. The larvae tunnel their way through stomach and intestinal walls, then mature and breed inside the human abdominal cavity.
The males die in there, but fertilized females migrate to the surface of the host's skin. They typically surface on the lower body, causing a painful blister. When the host dips the blister into the water for a little relief, the two-foot female bursts out of the blister and excretes her foul larvae to begin the cycle anew.
The entire human portion of this life cycle takes about a year, and that's when symptoms like fever, itching, nausea, vomiting, diarrhea and dizziness emerge in the host. If illness and parasitic violation weren't bad enough, secondary bacterial infections commonly result in painful disability that can disrupt the person's ability to work, attend school or care for family members. This disability period typically lasts 8.5 weeks, according to the Centers for Disease Control and Prevention, but it can sometimes prove permanent.
So you can see why The Carter Center has worked so hard to eradicate the parasite. Even Jimmy Carter — yes, that senior citizen and former president who builds Habitat for Humanity homes — stated, "I'd like for the last Guinea worm to die before I do."
And he's close to pulling it off!
Back in 1986, 21 African and Asian countries experienced a combined 3.5 million cases of guinea worm infection. By 2015, eradication efforts had cut that down by 99.99 percent, to just 22 cases in four countries. As of this writing, only seven cases have popped up in 2016.
But in the African nation of Chad, one of the last redoubts for Guinea worm survival, the parasites have seemingly jumped species. As reported by NPR, the worms have been popping up in dogs since 2013, sometimes to the tune of 60 or more parasites per host. Researchers are unsure exactly how the jump occurred and whether the dogs are acquiring the larvae from fish guts or perhaps frogs, but the threat is real.
And so an eradication effort that has exclusively focused on humans has been forced to consider canines as well. Don't worry, pet lovers, no one's aiming to cull Chad's dog population. Instead, The Carter Center is supplying people with collars, chains and $20 incentive payments to tie their dogs up away from the water supply for a two-week period — enough time for the female worms to emerge and die on dry land.
Researchers are confident in the plan, but the stakes are high. Our inhuman enemy has pivoted its reproductive strategy, potentially enabling it to survive and bounce back if our persistence falters.
We can't really attribute much agency to Guinea worm. Unlike the Thing, they can't operate a spaceship or imitate Wilford Brimley. They can't outsmart us, but nematode adaptive effectiveness is honed by up to a billion years of evolution, making it one of the oldest life-form lineages on the planet.
Let's hope we can pull it off.
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