Posted July 15, 2015
Lax biosecurity likely helped spread a highly pathogenic H5N2 avian influenza virus among farms, according to federal agriculture authorities.
The virus, which had caused the deaths of 48 million birds as of July 1 through a combination of infections and depopulation to control the outbreak’s spread, likely entered flocks through multiple routes, according to a June 15 report by the Department of Agriculture’s Animal and Plant Health Inspection Service.
New infections were found with less frequency by early June, with APHIS reports indicating the numbers of farms with new infections declined to one new case per week after June 5. In April and May, the agency had received a mean of three reports daily.
The H5N2 virus has spread to just more than 200 commercial farms since it was found March 4 in a Minnesota turkey farm, which itself followed seven other reports of the virus’s presence in backyard farms in the West. It spread to 150 turkey farms, affecting 8 million turkeys, and about 50 chicken farms, affecting 40 million chickens.
In the epidemiology report published in June, APHIS officials listed the following examples of possible contributors to transmission: equipment sharing among farms that included those with infections, lack of cleaning and disinfection of vehicles traveling among farms, and presence of rodents and wild birds inside barns housing poultry. The potential for the virus to also spread among farms by wind depends on virus shedding periods and distances the virus can travel on dust particles and remain viable, and details on virus survival characteristics were not yet available.
Air sampling had shown the presence of RNA from the highly pathogenic virus in samples collected inside and immediately outside infected premises, the report states, and some genetic material was detected at distances of up to 1 km. More investigation was needed, but agency officials “hypothesize that both the transport of airborne particles and the deposition of infectious airborne particles on the surfaces around infected premises represents a risk for the spread of HPAI to other locations.”
The report states that the virus was introduced to the U.S. through wild bird movement, but the numbers and proximity of affected farms indicated the virus was spreading in other ways. Samples collected from one cluster of farms with infections contained identical viruses, indicating the potential for transmission among those farms.
“In addition, genetic analyses of the HPAI viruses suggest that independent introductions as well as transmission between farms are occurring in several States concurrently,” the report states.
At the time the report was published, the agency lacked “substantial or significant enough evidence to point to a specific pathway or pathways for the current spread of the virus.”
In a separate message published earlier in June, APHIS Administrator Kevin Shea praised the “around the clock” work by hundreds of veterinarians in his agency to aid egg and turkey farmers in response to the outbreak. And he expressed pride in those efforts alongside state agriculture department veterinarians, agriculture industry members, and contractors.
“We take the trust placed in us extremely seriously, and I assure you that includes being ready to help producers and respond to outbreaks of serious livestock diseases,” he said.
He also said that, if needed, APHIS could call on a large network of food animal veterinarians and veterinary students “trained and ready to augment our response efforts.” And veterinarians set the policies and lead the teams responding to the most serious threats to livestock.
Shea also praised APHIS employees’ work in response to the outbreak as evidence the agency made successful investments in workforce planning, emergency response, and employee training “even as our appropriation has been consistently reduced over the last several years.”
“This will most likely be the most comprehensive response to a livestock disease in our Nation’s history,” he wrote. “We will carefully assess our efforts, and make sure that we continue to do all we can to build and support our veterinary workforce, which is the finest in the world.”
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