Follow-up testing at the US Department of Agriculture's (USDA's) National Veterinary Services Laboratories on the highly pathogenic H7 virus implicated in an outbreak at a Tennessee poultry farm indicates that the strain is H7N9 but is different from the H7N9 fueling outbreaks in China.
In other US avian flu developments, US agriculture officials yesterday reported a low-pathogenic H5N2 outbreak at a turkey farm in Wisconsin, the same day they announced the highly pathogenic H7 outbreak in Tennessee.
Tennessee H7N9 distinct from China lineage
In a statement, the USDA's Animal and Plant Health Inspection Service (APHIS) said the full genome sequencing reveals that all eight gene segments from the Tennessee H7N9 virus are from the North American wild bird lineage.
"This is NOT the same as the China H7N9 virus that has impacted poultry and infected humans in Asia," APHIS emphasized, adding that though the subtype is the same, the virus is different and genetically distinct from the China H7N9 lineage.
The outbreak at a commercial chicken broiler-breeder farm in Tennessee's Lincoln County, located in the south central part of the state, killed 700 of 72,800 birds.
The USDA said it continues to work with the Tennessee Department of Agriculture on the joint outbreak response and that surviving birds on the affected farm have been culled and burial is in progress. An epidemiologic investigation is under way to identify the outbreak source.
Federal and state authorities are conducting surveillance testing at poultry farms in an expanded 10-mile radius of the affected farm, and poultry movement restrictions have been put in place in a control zone to prevent the virus from spreading. As of yesterday, all commercial farms in the surveillance zone have been tested, and all of the tests were negative.
Commercial and backyard poultry will be monitored for illness, and all flocks in the surveillance are will be tested again.
The last H7 outbreak involving US poultry struck Indiana poultry farms in 2016. H7N8 was identified as the subtype, which hadn't been seen before in the United States. Most of the H7N8 outbreaks were low-pathogenic, but a highly pathogenic version was identified in one of the events, suggesting that the strain became more lethal as it spread.
Low-path H5N2 in Wisconsin turkeys
The low-path outbreak occurred at a commercial farm housing 84,000 turkeys in Barron County, located in northwestern Wisconsin, according to a notification from the World Organization for Animal Health (OIE). Authorities tested the birds after they showed signs of depression.
An investigation by the APHIS and the Wisconsin Department of Agriculture, Trade, and Consumer Protection is still under way. So far, test results have confirmed that the low-pathogenic H5N2 virus is related to the strain found in North American wild birds. However, genetic analysis shows that both the hemagglutinin (HA) and neuraminidase (NA) are distinct from H5N2 clade 18.104.22.168 viruses from 2015.
The facility has been quarantined, and the turkeys will be depopulated through controlled marketing of recovered birds.
The last low-pathogenic avian outbreaks in the United States occurred in 2016 and involved H5N1 at a turkey farm in Missouri and H5 avian influenza at live-poultry markets in three northeastern states.
Mar 7 APHIS press release
Mar 6 OIE report on low-pathogenic H5N2 in the United States
Mar 6 CIDRAP News story "High-path H7 avian flu detected on Tennessee farm"
Jan 15, 2016, CIDRAP News story "High-path H7N8 outbreak reported at Indiana turkey farm"
Jan 19, 2016, CIDRAP News story "H7N8 detections at more Indiana farms suggest mutation"