November 14, 2016

Dogs and Guinea worm eradication

Written by Mark L Eberhard, Ernesto Ruiz-Tiben, Donald R Hopkins

This post originally appeared on The Lancet.

Teresa Galán-Puchades, in her Correspondence on dogs and Guinea worm eradication, noted several critical points
about the Guinea Worm Eradication Program (GWEP) in Chad. We would like to clarify several of the issues. Dog infections have been addressed programmatically in Chad for the past 4 and a half years. The situation in Chad is different from previous reports of sporadic Guinea worm infections in dogs. What is not made clear by Galán-Puchade is that human Guinea worm has infected dogs occasionally,but when eliminated from the human population, dog infections disappear. By contrast, in Chad, dog infections are probably responsible for the small number of cases in human beings. We expect human infections in Chad to stop once transmission of Guinea worms among dogs is interrupted. Lastly, all evidence suggests transmission is not occurring via common drinking water sources, but via a paratenic aquatic host that people and dogs are eating raw or only partly cooked. Previous laboratory studies have shown that dogs (and cats and monkeys) are good experimental hosts for Dracunculus medinensis. Hence, the ease with which this infection was established in dogs is not surprising.

The reward paid to dog owners probably has a key role in dog infections being reported by owners, which is exactly what was hoped for. However, the increase in dog infection rates has resulted from active surveillance undertaken in larger and larger areas within Chad by the GWEP. Residents of endemic villages have been interviewed to learn what is known about Guinea worm disease. Discussions have also been held with former officials of Chad’s GWEP from 1993–98 to gain some insight and perspective on the matter. None of these reliable sources ever encountered a Guinea worm infection in a dog during years of working in endemic areas when hundreds of cases in human beings were being reported.

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