#16,162
While not viewed as posing a particularly severe pandemic threat, LPAI H9N2 is worrisome because it is ubiquitous in poultry in Asia, the Middle East, and increasingly in Africa. H9N2 continues to evolve (including signs of increased mammalian adaptation), and it is quite promiscuous, and able to reassort with a wide variety of other influenza subtypes (see below).
Viruses: PA From Recent H9N2 AIV Enhances H5N1 Infection In Mammalian Systems
EID Journal: Novel Reassortant HPAI A(H5N2) Virus in Broiler Chickens, Egypt
Virology: Receptor Binding Specificity Of H9N2 Avian Influenza Viruses.
J. Virology:Genetic Compatibility of Reassortants Between Avian H5N1 & H9N2 Influenza Viruses
H9N2: Avian Influenza A(H9N2) Y280 lineage [A/Anhui-Lujiang/39/2018] Virus
Low pathogenic avian influenza A(H9N2) viruses are enzootic in poultry in many countries in Africa, Asia, the Middle East, and Europe. Since the late 1990s when the first human infections with avian influenza A(H9N2) virus were identified, detection of this virus has been reported infrequently in humans and in swine and other mammals. In 2018, there were 7 reported human infections, most with known exposure to poultry and with the majority involving viruses of the Y280 lineage.
Summary: A risk assessment of avian influenza A(H9N2) Y280 lineage A/Anhui-Lujiang/39/2018 virus was conducted in July 2019. The overall IRAT risk assessment score for this virus falls into the moderate risk category. The summary average risk score for the virus to achieve sustained human-to-human transmission was 6.2. The average risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was 5.9, also in the moderate range. For a full report click here pdf icon[356 KB, 5 pages].
Granted, the numbers we have - even with this recent uptick - are believed to be significant undercounts. Most people in China (or elsewhere) who get minor-to-moderate flu-like symptoms never bother to see a doctor, or get tested.
Serological studies suggest human infection with H9N2 in Asia is far more common than the limited numbers we have would lead us to believe (see J. Infect & Public Health: High Seroprevalence Of Avian Influenza H9 Among Poultry Professionals In Pakistan).
Today the WHO Western Pacific Region Office reports one new H9N2 infection, the 15th case reported this year.
Human infection with avian influenza A(H9N2) virus
One new case of human infection with avian influenza A(H9N2) was reported from the National Health Commission of the People’s Republic of China to WHO on 30 August 2021. The case is a 20-month-old female from Changsha, Hunan Province, China with onset of mild illness on 23 August 2021 and was 3 hospitalized on 24 August.
The case had a history of exposure to domestic poultry prior to illness onset and no further cases were suspected among family members or any other close contacts at the time of reporting. This is the 15th case of avian influenza A(H9N2) reported from China in 2021. A total of 56 cases of human infection with avian influenza A(H9N2) have been officially reported from China to WHO since December 2015.
While LPAI H9N2 ranks fairly far down the pandemic threat 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.
