When an outbreak of highly pathogenic H5N1 avian influenza spread across North America this spring, researchers hoped for a replay of what happened after a different variant arrived in the United States. In a matter of months, more than 50 million birds died or were destroyed, costing farmers more than a billion dollars, but by June 2015, the virus was gone. When migratory birds returned from their summer breeding grounds in Canada, there was no poultry outbreak.
This is not the same as before. Warming temperatures failed to stop the spread of H5N1 in the United States and Canada over the summer. At least 99 wild bird species have been affected by the H5N1 outbreak in the United States, which is the most in a single year. The million-dollar question is whether migratory birds will cause more introductions in the fall.
If they don't, the virus may continue to circulate year-round, posing a permanent threat to poultry farming and wild birds. It is possible that impacts on wild birds will persist for a long time. Europe may show what is to come, as H5N1 has already become a fixture in wild birds and has caused bigger and bigger outbreaks over the past 3 years.
In 1996 H5N1 first appeared in poultry in China's Guangdong province, and since then it has caused several major outbreak around the world. The birds are able to spread the virus far and wide because it has evolved to not cause harm. Waterbirds are thought to have brought the disease to Canada from Europe. Bald eagles, owls, and other animals died after eating water birds. The Mississippi flyway is where snow geese and other species migrate. Farmers were forced to kill 40 million chickens and turkeys due to the disease. The virus began to move west in the spring.
More than 2000 birds have been found with H5N1 in the United States, compared with 99 during the 2015 outbreak. Wendy Puryear says that it has exploded in the breadth of the species she studies.
The infections started to fall in May. Rebecca Poulson is a wildlife disease researcher at the University of Georgia. She says that the scavengers are still being hit hard. Researchers in New England were surprised by a second wave of infections. It was like a switch had been flipped again.
Many sea birds nest in dense colonies. The populations of gannets crashed in parts of Canada. The Caspian terns were very hard hit by the lake. The wave of H5N1 has killed hundreds of harbor seals in Maine, and Puryear and colleagues are trying to figure out if the virus can spread between seals or if they all died from it. One human H5N1 case has been seen by the US and the UK.
The migratory birds, which come back to the United States from the north and could spread the virus, are the focus of all attention. Testing 1000 snow geese for H5N1 could take another month or two, according to the Canadian Wildlife Service. Live and hunter-killed ducks and geese are being tested.
Even if a new surge of infections arrives from the north, many researchers say the virus is already entrenched in some parts of the US. The consequences of that overlap could be serious. Richards says that farmers could face a constant risk of major losses, and that they would need to maintain or tighten their security measures.
There is still much to be learned. How H5N1 moves from one individual to another and between species is a mystery in wild birds. She says it will be a very complex story. It's difficult to predict, and we're nervous.
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