Avian Flu Diary: HK CHP Reports 2 More Mainland H9N2 Cases

https://www.chp.gov.hk/files/pdf/2021_avian_influenza_report_vol17_wk25.pdf

#16,031

This morning Hong Kong's CHP reported two more novel H9N2 infections from the Mainland - both from April - in today's weekly Avian Influenza Report, making a total of 13 H9N2 infections reported by China in 2021.

While most H9N2 infections are mild, their reported incidence has risen sharply in 2021. Whether this rise is more to do with better surveillance and reporting, or is propelled by increased transmission of the virus to humans, is unknown.

Granted, the numbers we have - even with the 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 those numbers would have us believe (see J. Infect & Public Health: High Seroprevalence Of Avian Influenza H9 Among Poultry Professionals In Pakistan).

A little over a year ago the CDC added a second lineage of the H9N2 virus to their IRAT (Influenza Risk Assessment Tool) short list of novel flu viruses with pandemic potential.

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].

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, it 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).