Much the same as we saw earlier today with the announcement that the HPAI H5N6 virus in Greece is not of the same lineage as the Asian H5N6 virus, this afternoon we learn the HPAI H7 virus detected over the weekend in Tennessee is an HPAI H7N9 virus - but of different lineage, and genetically distinct - from China's H7N9 virus.
And just as we saw last year with the emergence of an HPAI H7N8 At A Commercial Turkey Farm In Indiana, this H7N9 virus appears to be a reassortant comprised entirely of North American lineage avian flu gene segments.North American lineage LPAI and HPAI H7 viruses have caused poultry outbreaks in the past, and a small number of human infections have been reported, all described as minor.
- The CDC details two human infections with H7N2 viruses in the United States which occurred in 2002 and 2003. Both recovered completely.
- The Fraser Valley H7N3 outbreak of 2004 resulted in at least two human infections, as reported in this EID Journal report: Human Illness from Avian Influenza H7N3, British Columbia
- In 2012, HPAI H7N3 was associated with two minor human illnesses (see MMWR: Mild H7N3 Infections In Two Poultry Workers - Jalisco, Mexico).
- And just last December, a veterinarian caring for sick cats at a NYC shelter was mildly infected (see NYC Health Dept Statement On Human H7N2 Infection).
In 2008, researchers from the CDC, Emory University, and The Scripps Research Institute collaborated on a study of North American H7 viruses (see PNAS Contemporary North American influenza H7 viruses possess human receptor specificity: Implications for virus transmissibility).
While linked to only mild illness, they wrote:
We identified a low pathogenic H7N2 virus isolated from a man in New York in 2003, A/NY/107/03, which replicated efficiently in the upper respiratory tract of ferrets and was capable of transmission in this species by direct contact. These results indicate that H7 influenza viruses from the North American lineage have acquired sialic acid-binding properties that more closely resemble those of human influenza viruses and have the potential to spread to naïve animals.
H7 viruses, like all influenza viruses, continue to evolve, and adapt to new hosts - and outbreaks (and new reassortants) always deserve our attention.
The USDA's statement follows: We'll obviously be looking to seeing more epidemiological details, genetic studies, and the results of laboratory animal testing.
USDA’s National Veterinary Services Laboratories (NVSL) has confirmed the full subtype for the highly pathogenic H7 avian influenza reported in Lincoln County, TN. The virus has been identified as North American wild bird lineage H7N9 HPAI based upon full genome sequence analysis of the samples at the NVSL.
All eight gene segments of the virus are North American wild bird lineage. This is NOT the same as the China H7N9 virus that has impacted poultry and infected humans in Asia. While the subtype is the same as the China H7N9 lineage that emerged in 2013, this is a different virus and is genetically distinct from the China H7N9 lineage.
As additional background, avian influenza viruses are classified by a combination of two groups of proteins: hemagglutinin or “H” proteins, of which there are 16 (H1–H16), and neuraminidase or “N” proteins, of which there are 9 (N1–N9). Many different combinations of “H” and “N” proteins are possible. Each combination is considered a different subtype, and subtypes are further broken down into different strains. Genetically related strains within a subtype are referred to as lineage.
USDA continues to work with the Tennessee Department of Agriculture on the joint incident response. Birds on the affected premises have been depopulated, and burial is in progress. An epidemiological investigation is underway to determine the source of the infection.
Federal and state partners continue to conduct surveillance and testing of poultry within an expanded 10-mile radius around the affected premises to ensure all commercial operations in the area are disease-free. In addition, strict movement controls are in place within an established control zone to prevent the disease from spreading. As of yesterday, all commercial premises within the surveillance area had been tested, and all of the tests from the surrounding facilities were negative for disease. Officials will continue to observe commercial and backyard poultry for signs of influenza, and all flocks in the surveillance zone will be tested again.
The rapid testing and response in this incident is the result of extensive planning with local, state, federal and industry partners to ensure the most efficient and effective coordination. Since the previous HPAI detections in 2015 and 2016, APHIS and its state and industry partners have learned valuable lessons to help implement stronger preparedness and response capabilities.
More information about avian influenza can be found on the USDA avian influenza page.