#18,584
While HPAI H5N1 has remained the dominant H5 subtype around the globe, we've recently seen inroads made by an HPAI H5N5 subtype in Canada and parts of Europe (see The Continued Expansion of HPAI H5N5).
These new subtypes arise due to reassortment, which occurs when two different flu viruses infect the same host - share genetic material - and produce a hybrid.
Most reassortants will be unable to compete with their parental strains, but sometimes a new and viable subtype is created. HPAI H5N5 has shown some modest success in this regard, but it remains a minor player.
Today WOAH has reported (#6201) that a new HPAI H5N9 reassortment has been detected at a duck farm in Merced County, California. This HPAI subtype was last reported during the 2016/2017 H5N8 epizootic in Europe (see DEFRA: Update On HPAI & LPAI Avian Flu Outbreaks in France)
Details are scant, but they provide the following epidemiological data.
SOURCE OF EVENT OR ORIGIN OF INFECTION
- Unknown or inconclusive
EPIDEMIOLOGICAL COMMENTS
Highly pathogenic avian influenza (HPAI) H5N9, Eurasian lineage goose/Guangdong clade 2.3.4.4b and HPAI H5N1 clade 2.3.4.4b were confirmed in a commercial duck premises in Merced County, CA. This is the first confirmed case of HPAI H5N9 in poultry in the United States. The USDA Animal and Plant Health Inspection Service (APHIS), in conjunction with State Animal Health and Wildlife Officials, are conducting comprehensive epidemiological investigations and enhanced surveillance in response to the HPAI related events.
For now, this appears to be a one-off event, and there is no word on its pathogenicity. Whether HPAI H5N9 has `legs', and will spread beyond this duck farm - or will spontaneously appear elsewhere - remains to be seen.
But it does remind us that nature's gain of function (GOF) field experiment continues, and we should be prepared for surprises.
