Credit ECDC - Nov 2021
#16,515
When it comes to avian influenza viruses with pandemic potential, H5 and H7 subtypes are generally considered to pose the biggest threat, due to their ability to cause severe - and often fatal - illness in humans (see HK CHP: China Announces 5 More Human H5N6 Cases From December).
Luckily, none have yet acquired the ability to transmit easily from human-to-human, and have only caused sporadic outbreaks in humans.
These aren't the only avian threats, however, and one of the other subtypes we spend a good deal of our time watching is LPAI (Low Pathogenic Avian Influenza) H9N2 which is common in poultry in Asia, the Middle East, and parts of Africa.
Unlike the more virulent H5 and H7 avian viruses, it is not considered a `reportable' disease by the OIE, and so our understanding of its range and continued spread is limited.
While human infection with H9N2 has only rarely been reported over the past 2 decades (< 100 cases), it is almost certainly happens more often than we know (see J. Infect & Public Health: High Seroprevalence Of Avian Influenza H9 Among Poultry Professionals In Pakistan).
During the 2021 calendar year China reported 14 cases (see FluTrackers List) while one other was reported from Cambodia. That said - infection is usually mild, and testing for influenza is limited in much of the world - meaning a great many cases undoubtedly go unreported.
Over the weekend Macao reported on 4 additional H9N2 cases reported from the Mainland in November and December of 2021, and those cases are summarized below in today's Hong Kong Avian Influenza Report VOLUME 18, NUMBER 03.
Details on these cases are sparse; all were reported in children, and no outcomes were provided. Deaths from H9N2 infection, however, are exceedingly rare. We did see one fatality reported from China last November (see ECDC: A Fatal H9N2 Case In China & Risk Assessment), but no patient details were offered.
In May of 2020, the CDC added a new lineage (H9N2 Y280 lineage [A/Anhui-Lujiang/13/2018]) to their short list of novel flu viruses with at least some pandemic potential, although it would not be expected to gave the same impact as an H5 or H7 avian flu.
But H9N2's greatest claim to fame it its ability to reassort with other - sometimes far more worrisome - viruses. Often, when new HPAI flu strains emerge – if you look deep enough – you’ll find LPAI H9N2 was part of the process (see PNAS: Evolution Of H9N2 And It’s Effect On The Genesis Of H7N9).
Three years ago, in EID Journal: Two H9N2 Studies Of Note, we looked at two reports which suggest that H9N2 continues to evolve away from current (pre-pandemic and poultry) vaccines and is potentially on a path towards better adaptation to human hosts.
More recently, in J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China, a study from researchers from Shanghai Veterinary Research Institute and Wageningen University & Research, the Netherlands found the current inactivated virus vaccines used in China against H9N2 to be no match for this rapidly evolving pathogen.
While LPAI H9N2 ranks pretty far down our pandemic threats list - at least as a standalone virus - it's ability to reassort with potentially more dangerous avian, human, and swine flu viruses make it one to watch.
