Dogs stymie the battle to wipe out guinea worm.

As Nature notes, we’ve almost eradicated guinea worm – a terribly infectious parasite – but the worm seems to be striking back in the form of a mysterious dog disease:

The Carter Center in Atlanta, Georgia, is leading the global campaign to eradicate Guinea worm. Next week, it will announce that case numbers for the excruciatingly painful infection are at a record low, with approximately 25 cases reported in 2015 in just 4 countries: Chad, Ethiopia, Mali and South Sudan. But infections in dogs are soaring in Chad, where officials will meet at the end of January to grapple with the canine epidemic. The central African nation recorded more than 450 cases of Guinea worm in domestic dogs last year….

Researchers and officials strongly suspect that dogs are spreading the infection to humans; now the race is on to understand how this might happen, as well as how dogs acquire the infection in the first place. The World Health Organization is unlikely to declare Guinea worm eradicated until the parasite has stopped spreading in dogs, says [Liverpool parasitologist David] Molyneaux, who is part of the commission that will make that decision.

To better understand the situation, a team led by James Cotton and Caroline Durrant, genome scientists at the Wellcome Trust Sanger Institute in Hinxton, UK, is now sequencing the genomes of more Guinea worms collected from dogs and humans in Chad to confirm that dogs are indeed transmitting the disease to people. And Eberhard, who is convinced that this is the case, is trying to determine how dogs become infected in the first place. They are unlikely to contract the worms from drinking water, he says, because dogs tend to scare away copepods when they lap. Most of Chad’s cases have occurred among fishing communities along the Chari River, and Eberhard suspects that dogs are eating the entrails of gutted, copepod-eating fish. Dogs then pass the worms to humans by reintroducing the larvae into water.

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