New Bird Flu Strain Strikes in U.S.

A new strain of bird flu hit a poultry farm in Tennessee, but hasn't spread.


A new bird flu strain that struck a poultry farm in Tennessee and led to the culling of more than 73,000 birds is genetically different from the variety in China that’s killing humans, says the USDA.

On March 5, workers noticed an unusually high amount of dead birds in one of eight barns on a chicken farm in Lincoln County, TN., that supplies Tyson Foods. State officials were called in and it was determined that the broiler chickens were suffering from a highly pathogenic avian influenza called H7N9 (scientists classify bird flu by subtype and strain; genetically related strains in a subtype are called a lineage). Although the H7N9 is the same subtype as the Chinese version affecting humans that first emerged in 2013, it’s a different lineage and, thankfully, doesn’t infect people.

That’s good news since the H7N9 in China has infected more than 1,200 people since it was first reported in humans in April 2013, with a death rate of about 38.5 percent. Another difference is that the one found in Tennessee is highly pathogenic, meaning it tends to kill birds who contract it, while the Chinese version has been low pathogenic, which may sicken birds but not kill the. It was recently reported, however, that the Chinese strain has become more virulent in birds.

Suresh Mittal, a professor of comparative pathobiology at Purdue University, told Bloomberg News that the H7N9 found in Tennessee “is not a human virus yet” and while some avian influenza viruses are able to pass to humans, others stay within poultry. The Tennessee’s agriculture department, on its website, said the outbreak doesn’t present a risk to the food supply and that humans face a “very low” threat of infection when avian flu hits bird flocks. Even so, the state’s department of health and its agricultural department are, “out of an abundance of caution,” addressing “concerns about the health of individuals who are working on site or had contact with affected birds.”

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The USDA and state officials set up surveillance and testing of poultry within a 10-mile radius around the affected premises to ensure all commercial operations in the area are disease-free, and they have put strict controls in place to prevent spread. By this past Tuesday, all the nearby commercial flocks had been tested and came up negative for the virus.

“We’re very positive that we’ve taken care of it,” USDA chief veterinarian Jack Shere said during a USDA radio broadcast“There’s no evidence, based on the commercial flocks tested, in addition to the infected flock, of any spread at this time.”

The theory is that the flock somehow contracted the virus from a nearby pond where migrating waterfowl gather, according to the USDA. 

A second flock at a commercial breeding operation in Giles County, Tenn., was also hit by a case of H7N9 avian influenza on March 6, but it was a low pathogenic type. Officials from the Tennessee department of agriculture don’t believe the two cases are related.  The infected birds were culled, a 6.2-mile quarantine was placed around the facility and testing is taking place on other flocks in the area. So far no other flocks have tested positive.

New Bird Flu Strain Strikes in U.S.