Ducks contaminated by mercury pollution are significantly more likely to contract bird flu, a study found Wednesday, which points to another way in which man-made changes in the natural world are increasing the risk of virus spread.
Avian flu rarely infects humans, but persistent outbreaks in the US and UK and elsewhere have resulted in millions of poultry being killed so far this year.
Wild waterfowl like ducks are thought to be super-spreaders of the virus in part because they travel so far on their migration and potentially infect other birds along the way.
For the new study, scientists shot nearly 750 wild ducks from 11 different species in California’s San Francisco Bay, which is on a migratory path that stretches from Alaska to Patagonia.
They then tested the ducks for mercury contamination and whether they were infected with bird flu – or had antibodies to the virus in their system.
The findings, published in the journal Proceedings of the Royal Society B, showed that ducks contaminated with mercury were up to 3.5 times more likely to have contracted bird flu at some point in the past year.
The study’s lead author, Claire Teitelbaum, a quantitative ecologist at the USGS Eastern Ecological Science Center, said mercury contamination “can suppress the immune system, and that could make infection with anything — including influenza — more likely.”
San Francisco Bay is also a “significant hotspot for mercury contamination in North America … primarily from historic gold mining where mercury was part of that process,” she told AFP.
However, the ducks tested negative for the highly pathogenic H5N1 strain of avian influenza, which has been detected in many parts of the world.
– More bird flu likely –
Teitelbaum said that summer bird flu outbreaks in the United States have slowed “because many of the wild birds are further north on their breeding grounds.”
But “when they start coming down again, we’re likely to see a lot more activity,” she warned.
The spread comes as researchers are raising alarm that climate change, deforestation, ranching and other human-caused factors are increasing the likelihood of viruses crossing from animals to humans.
Teitelbaum said, “There are just so many ways humans have historically altered and continue to alter the natural environment.”
How pollution and contamination affects the risk of disease spread is “just another link we need to add to our more holistic view of what’s going on in the world,” she said.
Daniel Becker, a biologist at the University of Oklahoma who was not involved in the research, hailed the “impressive” study.
“There’s surprisingly little work looking at pollutant concentrations in wildlife and how they relate to infectious diseases,” he said, particularly for viruses that can spread to humans, like avian flu.
