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Great news! Cases of these horrifying, 31-inch parasites are dropping sharply.

The removal of the Guinea worm is a slow and painful process. (The Carter Center/L. Gubb)
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The CDC and the Carter Center released some great news about Dracunculiasis this Halloween season. It's not victory over sparkly vampires, though; cases of guinea worms (Dracunculus medinensis) decreased by 85 percent in 2015. The Latin name of “Little Dragon” refers to the fiery burning pain of these yard-long worms that live under human skin.

[Jimmy Carter wants the Guinea worm gone by the time he dies. Here’s why.]

No drug will control guinea worms, and there is no vaccine. The key to eradicating the worms is changing human behavior. Breaking habits doesn’t come easy, but the program has worked. In 1986, 20 countries reported 3.5 million cases of Dracunculiasis. In 2014, only four countries reported 126 cases of Guinea worm disease worldwide. The count for 2015 is currently 15 cases, in the same four countries: Chad, Mali, South Sudan, and Ethiopia.

Convincing those with actively emerging worms to stay away from water and get treatment is the only way to prevent new infections. “Any one person contaminating a village's water supply leaves that water supply contaminated for everybody,” said Donald Hopkins of the Carter Center.

Small crustaceans called copepods transmit the infection; they’re infected with immature Guinea worms. When people drink unfiltered water, digestion kills the copepods and releases the larval worms. The worms promptly burrow into the human’s abdominal cavity, become adults, and have sex.

A year after drinking contaminated water, an excruciating sore forms on the skin. Inside, the female worm waits. Once the infected human enters water, either to soak the painful blister or to do chores, the worm dumps her eggs and begins the cycle again.

Local village volunteers are key to treating and reporting infections. Local control of the program is what makes it succeed; it’s not a system imposed by outsiders.

Case reports are fascinating; a 54-year-old woman with an emerging worm was reported in September. Her 5-year-old granddaughter told her brother, who informed the village volunteer, and their Grandmother of Dragons received treatment.

[Watch doctors lure a worm out of a boy’s eye with … basil?]

Just as eradication efforts seem to be nearing an endgame, there’s an unexpected twist. Dogs can also be infected with Guinea worms, and they now must also be added to the control equation. Molecular tests confirmed that the worms found infecting dogs are the same species that infect humans — so the parasite won't truly be under control until canines are safe from it, too.

So far in Chad, 400 dogs have been confirmed with Guinea worm infections this year. It’s thought that dogs get infected by eating raw fish entrails discarded at fish markets, but more research is needed to confirm this.

Sharon Roy, Director of the WHO Collaborating Center for Eradication of Dracunculiasis at the CDC, explained dogs serve as a paratenic host, or an incidental host for the worms. “That’s the working theory in Chad. We haven't been able to find a smoking gun, or in this case a smoking fish,” she said.

Cash rewards encourage reporting of infected dogs, and tethering to keep them out of fresh water sources. Locals are also being encouraged to fully cook fish, and to dispose of fish entrails securely. The eradication campaign is close to completion, but it will take another year to know if 2015’s efforts are successful. “It’s not over til’ it’s over,” said Hopkins.

Gwen Pearson has a PhD in Entomology and is Outreach Coordinator for the Purdue Department of Entomology. She also blogs for WIRED. You can follow her on Twitter

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