Bird Flu Viruses Can Remain Infectious for Months in US Wetlands

vian influenza viruses can remain infectious within the surface water of northern US wetlands for a minimum of seven months, consistent with a study published yesterday (September 9) in Proceedings of the Royal Society B. employing a combination of lab and field experiments, researchers at the us Geological Survey (USGS) showed that viruses shed by wild ducks were still viable after quite 209 days in place , suggesting that these areas could act as environmental reservoirs for the pathogens while birds overwinter in areas further south.

“It’s saying to the scientific community we’d like to urge serious about the role the environment plays within the transmission of avian influenza,” says Chelsea Himsworth, a veterinary pathologist at the University of British Columbia and therefore the Canadian Wildlife Health Cooperative who wasn’t involved within the work. “The environment tends to be neglected” in disease studies, she says, but the new findings suggest “maybe viruses are hiding call at these waters, maybe they’re surviving for long periods, they’re re-infecting birds between migration cycles.”

Avian influenza, or bird flu, is caused by influenza A viruses, which are common in wild birds and may cause economically damaging outbreaks in poultry when transmitted via droppings or contaminated water or surfaces. Although avian influenza viruses typically pose no direct threat to humans, there are occasional reports of infections in people that work with domesticated birds and, very rarely, person-to-person transmission, making surveillance of the viruses a crucial public health focus.

Previous work by various research groups had already shown that avian influenza viruses could remain infectious in water for long periods within the lab, notes USGS research scientist Andy Ramey. But these studies typically use “really controlled settings,” he says. While such research is vital for learning about the consequences of temperature, pH, and other water conditions on virus viability, “it’s not really realistic of any ponds or lakes that I’m conversant in .”


USGS scientist Andrew Reeves retrieves samples in Alaska.
ANDREW RAMEY, USGS
To get a far better idea of the viruses’ persistence within the field, Ramey and colleagues collected and filtered water from wetlands in Alaska and Minnesota in late 2018, and inoculated those water samples with swabs taken from ducks. They then took half the samples to the lab to be maintained in constant conditions and put the opposite half into perforated steel drums that they left submerged within the wetland sites the samples had come from.

Initial genetic analyses of the lab-kept samples revealed several avian influenza strains like H3N8 and H4N6. By testing those samples monthly over the winter of 2018–2019, the team found that although the quantity of viable influenza virus declined over time, about 13 percent of the samples that had tested positive at the start of the experiment still yielded viable virus around seven months later.

Analyses of the wetland-stored samples in spring 2019 produced similar findings: around one-fifth of the samples that had contained viable virus at the start of the experiment still contained viable virus after 209–229 days stored in place . Genetic sequencing confirmed that the viruses at the top of the experiment were an equivalent ones detected at the beginning—not the results of environmental contamination, Ramey says.

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