New research suggests that dogs eating contaminated fish are hampering efforts to eradicate a human parasite disease.
Guinea worm disease is mainly contracted by drinking water contaminated with parasite larvae carried by water fleas.
After mating and growing inside the body for 10-14 months, the one-metre-long adult worm emerges, generally from the arms or legs, to shed its larvae back into the water.
In some of the world’s poorest communities in Chad, Ethiopia, Mali, and South Sudan, the parasite causes disability and trauma.
Guinea worm cases in humans have reduced from millions in the 1980s to just 27 in 2020 as a result of eradication programs.
Guinea worm would be the second human disease to be wiped out, following smallpox.
Just as eradication appeared to be on the horizon, it was discovered that domestic dogs are also carriers of the parasite.
Guinea worms were found in 93 percent of dogs in Chad, central Africa, in 2020, according to targeted surveillance.
The University of Exeter’s research, published today in Current Biology, uncovered a novel mode of transmission: dogs eating parasite larvae-infected fish. This means that dogs continue the parasite’s life cycle and humans are still susceptible to infection.
The researchers spent a year in Chad, working in many of the worst-affected villages along the Chari River.
They used satellite tags to follow hundreds of dogs’ movements and forensic stable isotope analysis of dog whiskers to determine their meals throughout the year.
The majority of fish consumed by the canines – mostly guts or smaller fish – were discarded by humans fishing on the river and its lagoons.
The study’s lead author, Professor Robbie McDonald of Exeter’s Environment and Sustainability Institute, stated: “Dogs are now the key impediment to eradicating this dreadful human disease.
“Our work shows that fisheries, and the facilitation of dogs eating fish, are likely contributing to the persistence of Guinea worm in Chad.
“The challenge now is that this pathogen must be eliminated not only from people but also from animals.
“This is a clear example of where a ‘One Health’ approach to integrating health of people, animals and the environment is required to eradicate this debilitating human disease.”
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