More than 10 percent of U.S. chickens raised to produce eggs were killed this spring by or because of a highly pathogenic avian influenza virus.
As a result of the outbreak and resulting depopulation efforts, some of which were pending at press time, the H5N2 virus had affected 39 million chickens—at least 33 million of which were laying hens—and 7 million turkeys by June 9, according to a combination of figures from the Department of Agriculture and state agencies. This included 29 million chickens in Iowa and 5 million turkeys in Minnesota.
Three other states each had more than 1 million affected birds: Nebraska, South Dakota, and Wisconsin.
The resulting reduction in the egg supply was potentially the largest ever short-term change in the U.S. egg market, according to Maro Ibarburu, associate scientist for the Egg Industry Center at Iowa State University. He wrote that analysis in a report published May 8, when only 22 million laying hens had died.
In another article, Brigid Tuck, senior economic impact analyst for the University of Minnesota Extension, predicted a ripple effect from the outbreak, as reflected by an announcement that Jennie-O would temporarily lay off 233 workers at a turkey processing plant starting May 26 because of the reduced supply of birds.
The USDA’s indemnity commitments for depopulation of flocks appraised as of June 4 totaled $177 million.
Iowa Gov. Terry E. Branstad declared a state of emergency, giving state agencies access to more resources for disease response. In a press conference, he said the outbreak was a disaster of a magnitude “much greater than anything we’ve dealt with in recent, modern times.”
Multiple perspectives needed
Chad Gregory, CEO of the United Egg Producers, said in a statement that egg farmers have responded to the highly pathogenic viruses by implementing extensive biosecurity measures and taking precautions such as restricting access to farms, preventing hen exposure to wild birds, increasing veterinary monitoring of flocks, and using protective clothing.
Steve Olson, executive director of the Minnesota Turkey Growers Association, said turkey growers are open to use of vaccines if needed to keep flocks healthy, although vaccination has trade implications because diagnostic tests cannot distinguish between vaccinated and infected birds. Some workers exposed to turkey flocks also have been receiving antiviral drugs in efforts to prevent the spread of the virus through humans to other birds.
No humans are known to have been sickened by the outbreak of H5N2 infection, according to the Centers for Disease Control and Prevention.
Olson said that most turkey growers raise and sell three flocks yearly, and many of those affected would be down to 1.5 flocks.
Surveillance by state fish and wildlife departments and the federal Department of Agriculture also have found that Cooper’s hawks, red-tailed hawks, a bald eagle, a peregrine falcon, and a great horned owl were infected with H5 avian influenza viruses when they died, according to USDA reports. The viruses also have killed several captive gyrfalcons and falcons.
Dr. Julia B. Ponder, executive director of The Raptor Center at the University of Minnesota College of Veterinary Medicine, noted that these influenza viruses appear to cause acute infections in raptors, with quick deaths. But the prevalence of the viruses in wildlife and effects on susceptible populations are unknown.
Dr. Carol Cardona, the Pomeroy Chair in Avian Health at the University of Minnesota, said studies on the H5 avian influenza viruses’ effects need to cross scientific disciplines covering domesticated animals, wildlife, and pathogen movement.
“We have multiple perspectives that need to come together to solve this,”
Dr. Cardona said. “It’s not going to be solved by domestic animal folks talking amongst themselves.”
Emergence in West
The H5N2 virus was discovered in domesticated birds in January, first in mixed bird flocks in Washington and then in Idaho. It followed discovery in December 2014 of a related, also highly pathogenic H5N8 avian influenza virus, which was first found in a captive gyrfalcon in Washington and then in a mixed bird flock in Oregon.
Through May, the H5N8 virus had been found in only two commercial flocks, a 130,000-turkey farm and a 113,000-chicken flock, both in California. But since March 4, when the H5N2 virus was found in a 26,000-turkey flock in Minnesota, it has spread to at least 150 other commercial turkey flocks and 49 commercial chicken flocks.
The H5N2 virus has been found in the Mississippi, Central, and Pacific flyways. But it has remained undetected in the Atlantic flyway where, three decades earlier, another highly pathogenic H5N2 avian influenza strain killed millions of birds.
Starting in October 1983 and extending into 1984, that outbreak led to the destruction of 17 million birds, mostly chickens and largely confined to Pennsylvania, according to a combination of JAVMA archives and documents from the USDA and Environmental Protection Agency.
Dr. Cardona, at the University of Minnesota, noted that USDA tests indicated some of the first H5N2 and H5N8 isolates identified could spread by contact among turkeys but not spread easily through contact among chickens.
“I think that’s why the chicken flocks, at first, seemed to be resistant,” she said.
Dr. David E. Swayne, director of the Southeast Poultry Research Laboratory of the USDA Agricultural Research Service in Athens, Georgia, said tests on viruses isolated in December 2014 showed that respiratory exposure required high quantities of virus to infect chickens and turkeys, with slightly lower amounts needed in turkeys. Infected turkeys transmitted the virus through contact with naive turkeys, and less transmission occurred among chickens, he said.
Those results suggested the initial viruses were more infectious and transmissible for turkeys, and the ARS has been conducting studies to determine whether the viruses circulating in the Midwest are also more infectious and transmissible for turkeys than for chickens.
Dr. Cardona noted that influenza viruses evolve and reassort as they pass through birds. Influenza virus is always changing, she said. “It is intellectually exciting, but the tragedy around this is just really hard to get around,” she said.