#15,917
We continue to get reports, both belated and more recent, out of China of human H9N2 infection (see last month's WHO WPRO: China Reports 3 Additional Human H9N2 Cases), and while most reported cases are mild, their incidence appears to be increasing.
Due to a lack of testing, we are only aware of a few dozen cases (see FluTrackers List), but serological studies suggest human infection is far more common than official numbers would have us believe (see J. Infect & Public Health: High Seroprevalence Of Avian Influenza H9 Among Poultry Professionals In Pakistan)
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).
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
All reasons why, last May, 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].
We have a few additional details on the two latest human H9N2 infections reported from China in the latest edition of the WHO Western Pacific Regional Office Avian influenza report. Of note, more than 20% of the human H9N2 infections reported by China since 2015 have been reported (some belatedly) since Jan 1st, 2021.
(Excerpt)
Human infection with avian influenza A(H9N2)
Two new cases of human infection with avian influenza A(H9N2) virus detected through influenza-like illness (ILI) surveillance in China were reported to WHO.
The first case is a 10-year-old male from Sanming, Fujian Province, China with illness onset on 28 January 2020. The second case is a two-year-old female from Shiyan, Hubei Province, China with illness onset on 7 February 2021. Both cases had mild illness and have recovered.
The case from Hubei Province had exposure to backyard poultry while no history of Avian Influenza exposure was reported for the case from Fujian Province. As of the time of report, no family clusters were reported.
To date, 12 cases of avian influenza A(H9N2) have been reported in the Western Pacific Region in 2021 and a total of 53 cases of human infection with avian influenza A(H9N2) have been reported in the Western Pacific Region since December 2015.
Four years ago, the biggest avian flu threats were H7N9 and H5N1. But in 2017 China deployed a nationwide H5+H7 poultry vaccination program that greatly suppressed those subtypes. While incredibly successful, it did nothing to curb H9N2, and since then we've seen that subtype flourish in Asian poultry (see OFID: Avian H5, H7 & H9 Contamination Before & After China's Massive Poultry Vaccination Campaign).
While avian and swine novel flu have been pushed out of the headlines by COVID-19, both continue to evolve, spread, and flourish around the world. We've seen a huge resurgence in HPAI H5Nx in poultry and wild birds over the past 6 months, and a spike in human H5 infections.
HK CHP Notification: Fatal Human Case of Avian H5N6 In Guangxi Province, China
WHO Statement & Risk Assessment On Human Infection with Avian H5N8 – the Russian Federation
China's Recent Resurgence Of Human HPAI H5N6 Infections
In addition to tracking 3 North American Swine Variant viruses, ten weeks ago the CDC added the EA H1N1 `G4' virus to their IRAT list (see CDC Selects New Swine-Variant EA H1N1 Virus For The Top Of Their IRAT List), giving it the highest risk assessment of any of the 20 novel viruses on their list.
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.
And right now, even a mild flu pandemic would be an unwelcome complication during our COVID crisis.
