Mercury pollution increases vulnerability to bird flu

Wild ducks contaminated with mercury are more likely to be affected by bird flu, a study revealed Wednesday, which again points to the impact of environmental pollution associated with human activities on the spread of viruses.

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Wild ducks are considered the main vectors of avian influenza, particularly because of their migrations: during their long journeys they can infect many farm birds (ducks, chickens, geese, etc.) where this viral disease is particularly deadly.

For this study, published in the Royal Society’s biological research journal Proceedings B, scientists shot nearly 750 wild ducks of 11 different species in San Francisco Bay, USA, which is on a migratory corridor from Alaska to Patagonia.

Knowing the harmful effects of certain heavy metals on immunity, they measured the levels of mercury in people’s blood in the lab, while simultaneously testing for avian flu infection — or the presence of antibodies to the virus.

Result: Ducks contaminated with mercury – mainly via the food chain – were up to 3.5 times more likely to contract the disease over the course of the year. And the higher the concentration of mercury, the higher the prevalence of antibodies.

The study says the ducks tested negative for the highly pathogenic strain of the H5N1 virus, which has been identified in numerous outbreaks around the world.

Avian influenza, which is generally asymptomatic in wild birds, can become highly contagious and deadly when transmitted to its congeners on farms.

fear of resurrection

The accumulation of mercury in the body anyway “can suppress the body’s immune responses and make it more vulnerable to all infections, including avian flu,” Claire Teitelbaum, an ecologist at the US Geological Survey, a branch of which is dedicated to wildlife conservation, told AFP.

San Francisco Bay is also a “hot spot of mercury contamination in North America, due to the historical activity of gold mines that used mercury in their extraction,” adds the researcher, lead author of the study.

In the United States, the animal disease slowed in the summer because “many wild birds were returning to their nests,” farther north. But “when they start coming down again, we’re likely to see a rebound,” she predicts.

That year, Europe also faced an episode of bird flu on an unprecedented scale, leading to the slaughter of tens of millions of poultry, particularly in France and Italy.

The study on these “super-contaminating” ducks comes as experts continue to sound the alarm about the impact of climate change, deforestation and pollution-related human activities on wildlife that favor zoonoses, diseases transmitted from animals to humans.

While most avian viruses do not infect humans, some subtypes manage to cross the species barrier, such as the H5N1 virus, pathogenic to humans and found in Asia.

Studying how pollution increases the risk of virus spread, Claire Teitelbaum adds “a building block to a more global vision of what’s happening in the world”.

“Surprisingly, little work has addressed the links between wildlife contamination and viral infections,” comments Daniel Becker, a biologist at the American University of Oklahoma, who welcomes the results of this study, in which he did not participate.

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