Although avian flu reports have been in unusually short supply this winter from China - with only 1 H5N6 human infection, and 3 H7N9 cases - we learn from the latest (March 2nd) WHO Influenza at the human - animal interface report of 3 new H9N2 infections between late December and the middle of February.
All three cases were described as `mild', and 2 of the 3 had recent exposure to poultry. In 2017, China reported 5 cases, while the year before, China reported 7 cases and Egypt reported 1 (see FluTrackers Global Cumulative H9N2 Partial Case List 1998-2017).
Over the past 2 decades just over 3 dozen human H9N2 infections have been recorded in 3 countries (China, Egypt & Bangladesh). That number is undoubtedly both under diagnosed and underreported as the virus is endemic in poultry across Asia, the Middle East, and has recently moved into Africa.A 2014 seroprevalence study, found antibodies against H9N2 ranged from 5.9% to 7.5% among poultry exposed individuals in Egypt, suggesting human infection is far more common than the official tallys would suggest.
On the positive side, H9N2 infection in humans has generally been mild, and no human-to-human spread has been detected.H9N2 is viewed as having some pandemic potential (see CDC IRAT SCORE), and so several candidate vaccines have been developed over the years.
The avian H9N2 virus occupies a special spot in our bird flu coverage because - while (until recently) only seen as an LPAI (low pathogenic) virus in poultry - its internal genes routinely make up the backbone of many of the HPAI viruses that pose the greatest risks to both poultry, and human health.
In the past, we’ve looked at this propensity of the H9N2 virus to reassort with other avian flu viruses (see PNAS: Reassortment Of H1N1 And H9N2 Avian viruses & PNAS: Reassortment Potential Of Avian H9N2) which have shown the H9N2 capable of producing `biologically fit’ and highly pathogenic reassortant viruses.
Nearly 4 years ago, in PLoS Path: Genetics, Receptor Binding, and Transmissibility Of Avian H9N2 researchers found evidence of Chinese H9N2 viruses binding preferentially to alpha 2,6 receptor cells - the type commonly found in the human upper respiratory tract - rather than to alpha 2,3 receptor cells.Five weeks ago, in A Curious OIE Notification From Ghana: HPAI H9N2?, we saw what appears to have been the first detection of an HPAI (Highly Pathogenic) H9N2 virus in West Africa.
While we are still awaiting clarification and detailed analysis of this HPAI strain, this is a reminder that avian flu viruses are perfectly capable of changing on a dime, and are quite capable of throwing us curve balls.