A case of bird flu at a Tennessee farm has been identified as highly-pathogenic H7N9 avian influenza, while distinct from an infectious variety in China.
The type is “a different virus and is genetically distinct” from China’s H7N9 bird-flu strain that has sickened poultry and infected humans in Asia, the U.S. Department of Agriculture said in a statement Tuesday. The variety found in the U.S. is from North American wild bird lineage, the agency said. Humans face a “very low” threat of infection during bird-flu outbreaks in poultry flocks, according to a release earlier this week from Tennessee’s agriculture department.
Highly-pathogenic avian influenza, which can be deadly to domesticated poultry, was confirmed at a Lincoln County, Tennessee chicken operation on March 5, near the Alabama border. The flock of 73,500 birds was a breeding operation that supplied Tyson Foods Inc. All the birds have been destroyed and burial is in process, according to USDA.
“We’re very positive that we’ve taken care of it,” USDA chief veterinarian Jack Shere said in a broadcast dated Monday that was posted to the agency’s website. “There’s no evidence based on the commercial flocks that have been tested, in addition to the infected flock, of any spread at this time.”
Several countries, including Japan and South Korea, have restricted U.S. poultry imports from Tennessee this week.
Officials are testing poultry within a 10-mile radius of the Lincoln County farm, the USDA said Tuesday. That was up from an initial area of 6 miles.
The zone was increased “out of an abundance of caution,” Worth Sparkman, a spokesman for Tyson, the largest U.S. chicken producer, said in an email Tuesday.
As of Monday, all other commercial poultry farms within the area were negative for the disease, the USDA said. Tennessee’s agriculture department also said that poultry in the region have tested negative so far, and Alabama’s state veterinarian office said backyard poultry flocks in the area didn’t have the virus in a first round of testing.
The strain of H7N9 bird flu found in the U.S. is a poultry virus only, according to Suresh Mittal, a professor of comparative pathobiology at Purdue University.
“It is not a human virus yet,” Mittal said by phone. Some avian influenza viruses are able to pass to humans, while others stay within poultry, he said.
In China, human infections of a new H7N9 avian influenza virus were first reported in March 2013, and annual epidemics have occurred since then, according to the Centers for Disease Control and Prevention. In the five months ended Feb. 27, 460 cases of infection were reported in China and nearby regions in the fifth wave of human infection, the World Health Organization said. More than 70 deaths have been reported in the country.
While the Tennessee Department of Health is monitoring workers who were involved with depopulation at the Lincoln County farm, no human health concerns are expected and the CDC has indicated there is minimal risk to people, John Dunn, the department’s deputy state epidemiologist, said by phone.
A case of low-pathogenic avian influenza has also been detected at a turkey farm in Barron County, Wisconsin, according to the World Organisation for Animal Health. Low-pathogenic strains typically cause only minor symptoms in birds.