Wild ducks are reputed to be major vectors of avian flu, in particular because of their migrations: during their long journeys, they are likely to contaminate many farmed birds (ducks, chickens, geese, etc.), in which this viral disease is particularly deadly.
750 wild ducks slaughtered
For this study, published in the Royal Society’s biological research journal, “Proceedings B”, scientists killed nearly 750 wild ducks from 11 different species in San Francisco Bay (United States), located on a migration corridor from Alaska to Patagonia.
They measured in the laboratory the level of mercury contained in the blood of individuals and, in parallel, tested an infection with avian influenza or the presence of antibodies against the virus.
Result: ducks contaminated with mercury – mainly via the food chain – had up to 3.5 times more risk of contracting the disease during the year. And the higher the mercury concentration, the higher the prevalence of antibodies. The study states, however, that the ducks tested negative for the highly pathogenic strain of the H5N1 virus, detected in many homes around the world.
Suppression of immune reactions
Avian flu, generally asymptomatic in wild birds, can become very contagious and deadly by being transmitted to their congeners in farms.
The accumulation of mercury in the body can anyway “suppress the immune reactions either of the body, exposing it more to all infections, including avian influenza”, explains Claire Teitelbaum, ecologist at the American scientific institute US Geological Survey.
In the United States, the epizootic slowed down during the summer because “a lot of wild birds were returning to their nests”, further north. But “when they start to come down, we’re probably going to see a resurgence,” she predicts.
This year, Europe also faced an episode of avian flu on an unprecedented scale, leading to the slaughter of tens of millions of poultry, particularly in France and Italy.
Alert on pollution linked to human activities
The study on these “super-contaminating” ducks comes as experts continue to sound the alarm on the impact of climate change, deforestation and pollution linked to human activities on wildlife, favoring zoonoses , diseases transmitted to humans by animals.