by Jean Cypher, DVM
Avian influenza is an interesting ecological and cultural story: The virus has been around for millennia, apparently co-evolving with waterfowl, which carry and shed it, but exhibiting very few symptoms. Technology improved enough to detect it in the 1980s, when we suspected that it was being passed between Asian poultry, pigs and migrating birds. Then the latter passed a strain of the virus to seals off the U.S. West Coast, causing mass mortality.
Today the virus has been identified as a single-strand RNA virus (the kind that tends to mutate a lot) with 144 permutations or strains of the virus. It is found mostly found in dabbling ducks, and sometimes in other aquatic birds.
Things got interesting late last year because wild ducks brought the H5N2 and H5N8 strains of the virus south on their fall migration.
A couple of strains have shown up in poultry, causing death often in less than 48 hours. The viral strains that are deadly for poultry are called “highly pathogenic avian influenza” HPAI (as opposed to LPAI). These strains aren’t causing disease in humans.
Things got interesting late last year because wild ducks brought the H5N2 and H5N8 strains of the virus south on their fall migration. This January, chickens and guinea fowl in backyard flocks in southern British Columbia started dying – and then in Winston, Oregon, then on the Oregon/Idaho border, and then at a commercial poultry operation in California. Those outbreaks had to be controlled by killing all the poultry (144,000 at one commercial poultry facility). In the meantime, several Idaho gyrfalcons fed duck meat from an Oregon hunter caused the falconer’s gyrfalcons, as well as a wildlife rehabilitator’s great horned owl, to die.
The strains causing problems here were traced to Southeast Asia. Wild ducks took them north and mixed with birds in the Siberian and Pacific flyways. The strains were also carried 10,000 miles west to northern Europe in the summer of 2014. There is a lot of mixing of birds between all the flyways.
The virus dies quickly when exposed to sun and air. But it can live for weeks in cool, moist habitat. So muddy shores of northern ponds are good sources of infection. Waterfowl shed it in the feces, although it is also in the meat and organs, causing predatory birds to get sick. Poultry usually catch it by exposure to duck droppings. Poultry pass it to one another by coughing and sneezing.
Thirty countries have instituted some kind of embargo, regional or nationwide, of U.S. poultry. Those countries won’t lift their trade embargoes unless we follow international protocol for containing and eradicating the disease in domestic flocks. So if a backyard flock gets infected, all the poultry and domestic ducks are killed, even though the latter would probably survive. The birds most at risk are free-range poultry that have access to water where wild ducks congregate or where wild ducks are flying into chicken yards to panhandle some free food.
When birds migrate along the Pacific Flyway, some move far north-to-south, and many move just a bit: Arctic to Canada, or Canada to Oregon. Most of the sampling information comes from swabs of hunter-killed wild ducks. Since hunting season occurs only during the fall migration, we don’t know if the birds overwintering to the south of Oregon, which will return to us this spring, may also be carrying the disease. So there may or may not be outbreaks among poultry this spring. The virus may spread east across the U.S. or these variants could just peter out in the wild population.
Unfortunately, this development is a game-changer for how people live with free-range chickens and other poultry and wild waterfowl on the West Coast. Until further notice, it’s not safe for anyone who raises chickens to let their birds be exposed to wild duck feces and it’s not safe for falconers to hunt their birds on ducks.