#18,627
For the second week running Hong Kong's CHP Avian Influenza Report is announcing 2 more H9N2 infections on the mainland (see last week's blog). Over the past 6 months Mainland China has reported 17 such cases, although the actual number of infections is thought to be much higher.
In addition to > 140 confirmed human infections (see FluTrackers list), seroprevalence studies have shown people with exposure to infected poultry often develop H9 antibodies, suggesting mild or asymptomatic infection.A bit unusually, both cases reported this week are older adults (F, 72 & 56). Most of the cases reported by China have been children or adolescents (14 of the past 17 cases). While most H9N2 have been mild or moderate, at least 2 deaths have been reported.
H9N2 is poorly controlled in Chinese poultry, despite the long-term use of vaccines (see J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China), which has led to the creation and spread of numerous of genotypes.
A reminder that livestock vaccines must be well-matched, properly applied, and continually updated (see MPR: Poultry AI Vaccines Are Not A `Cure-all’ & The HPAI Poultry Vaccine Dilemma) if they are to be effective.
Over the past 15 years we've watched as H9N2 has expanded its geographic range - spreading out of Asia into Europe, the Middle East and Africa. While it occasionally spills over into humans, H9N2's biggest threat may come from its unique ability to reassort with other, potentially more dangerous, avian viruses.
Its internal genes have often been found inside many HPAI viruses (including H5N1, H5N6, H7N9, and most recently zoonotic H3N8) - (see The Lancet's Poultry carrying H9N2 act as incubators for novel human avian influenza viruses).
H9N2 is such a versatile virus, it has even been detected in Egyptian Fruit bats (see Preprint: The Bat-borne Influenza A Virus H9N2 Exhibits a Set of Unexpected Pre-pandemic Features).
Seven years ago, in EID Journal: Two H9N2 Studies Of Note, we looked at two reports which suggested 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.
While admittedly not at the very top of our list of pandemic concerns, the CDC has 2 different lineages (A(H9N2) G1 and A(H9N2) Y280) on their short list of influenza viruses with zoonotic potential (see CDC IRAT SCORE), and several candidate vaccines have been developed.
