Some waterfowl have immunity to avian flu but when it is passed on through feces it becomes highly pathogenic
KANSAS CITY, Mo. — Migrating waterfowl crossing the Bering Strait may be responsible for carrying a virus that killed 50 million chickens and turkeys in the United States last year.
Ducks, geese, gulls and terns can carry the killer avian influenza virus as they migrate but rarely succumb to it themselves, said Thomas DeLiberto, a veterinarian with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service.
“They can get infected, they can shed virus and they show little to no clinical signs,” he said at the National Institute for Animal Agriculture’s April 3-7 annual meeting in Kansas City.
The highly pathogenic form of the virus became the most serious animal health crisis to affect the U.S. Starting on the West Coast, it eventually affected 232 premises throughout the country at a cost of $3 billion for producer payments and clean up. Of those, 211 were commercial and 21 were backyard operations.
Many infected operations are still in recovery mode.
Wild fowl seem to have natural immunity, but the virus changes from low pathogenic to highly pathogenic once they pass it on through feces or other forms of shedding.
“Wild birds, depending on the species and time of year, can move hundreds if not thousands of miles in a few days during the incubation period and shed viruses through that whole time period,” he said.
These viruses probably started in Asia and hopscotched to Europe. It was not expected to show up in North America because of the distance.
The first cases appeared in South Korea in January 2014, when domestic ducks were infected. It appeared to be eradicated, but in April 2014 the virus showed up in Japan in domestic birds and in wild bird feces.
Migratory birds headed north that spring, and the virus was found in China during late summer and early fall. It was detected in November in Germany, the Netherlands and the United Kingdom as birds started to move again.
A highly pathogenic form was found in British Columbia in late November and ended up in the Pacific Northwest by December. This region coincides with the Pacific migratory flyway.
Monitoring wild birds is difficult, although researchers would like to follow them to see how these viruses evolved and were distributed to affect so many poultry operations.
Numerous poultry operations near the Great Lakes were infected, but scientists do not know if wild birds in this region were responsible because there is limited data.
It is not likely that the virus found in the Midwest came from Washington or California, said DeLiberto.
The birds probably introduced the virus much earlier in the fall, but it was not detected because no one was looking for it.
Dabbling ducks such as mallards, terns and pintails that tip up when they feed in the water do not seem to be harmed by the virus, but Canada geese and raptors are more likely to die from it.
Researchers also checked other wildlife, such as sparrows, starlings, pigeons, rats, skunks and raccoons, but didn’t find the virus.
It is hard to find dead birds be-cause nature takes care of them quickly, but more than 45,000 birds have been checked since last July. Two positives were found in mallards, but they did not necessarily die of disease.
DeLiberto said these viruses are like an invasive species, and resident viruses usually out-compete or incorporate them. However, the invaders could also linger and cause more trouble.
“It is probably still circulating in the environment, but we don’t know which way it is going to go yet,” he said.
Many farmers might prefer to shoot the wild birds feeding in their fields, but they are the wrong target.
The greater risk is actually standing water rather than the birds leaving feces on a poultry operation.
“Water is a huge risk in my mind, much higher than a mallard flying over the property,” he said.
Equipment and people move through contaminated puddles and ponds and then spread it to the farm.
Most producers know they should never use untreated surface water to water poultry and clean equipment and barns.
A good biosecurity plan could include removing vegetation from banks of man-made water structures, fencing off areas to separate people and equipment from water and natural vegetation and adding deterrent devices to discourage birds from landing there.