When it comes to avian influenza, more commonly known as bird flu, all birds are not created equal.
“The scientific community has become accustomed to speaking about influenza viruses in birds as a group, but birds are an incredibly diverse taxa of animals with different natural history, physiology, and anatomy,” says Jonathan Runstadler, professor and chair of the Department of Infectious Disease & Global Health at Cummings School of Veterinary Medicine at Tufts University.
Runstadler is one of the authors of a new study, published today in the journal PLOS Pathogens, which takes a data-driven look at influenza viruses circulating among different groups of birds and characterizes which types of birds are involved in spreading the virus. The timing of this paper is impeccable, as a highly pathogenic strain of bird flu has been spreading across North America.
This lineage of bird flu originated around 1996 and was first found in a domestic goose in China. The virus mutated and persisted, and the first big wild bird outbreak happened around 2005 in a major wetland in central Asia. Subsequent changes in the virus led to a 2014 introduction to the U.S. via the Pacific Northwest, severely affecting the U.S. poultry industry and forcing the culling of about 40 million turkeys and chickens as a control measure.
“It was a big blow,” says Nichola Hill, lead author of the paper and an assistant professor of biology at University of Massachusetts Boston, who worked in Runstadler’s lab at Cummings School for nearly five years. “After it ended, we knew that we were between outbreaks and there was a high probability of an outbreak happening again. We felt we needed to look at long-term, historical data to find patterns and determine which birds are really driving global spread. So we compared birds at a finer taxonomic scale than prior studies such as wild ducks, gulls, land birds, and geese versus domestic poultry like chickens, and we came up with some really interesting findings.”
Historically, ducks like mallards have been considered super-spreaders of avian influenza, infecting wild birds and backyard poultry alike, and Hill and Runstadler’s research found that to be broadly true. Dabbling ducks are powerful vehicles for spreading the virus and for the evolution of the virus in the wild bird reservoir. They can carry highly pathogenic strains and be completely asymptomatic, plus they swim and fly so they can move the virus in a variety of ways, including into local water bodies.
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