Tuesday, March 02, 2021

WHO WPRO: China Reports 3 Additional Human H9N2 Cases

 Credit HK Weekly Avian Influenza Report VOL 17, NUM 09


Reports, both belated and more recent, of human infections from avian H9N2 continue to emerge from China, with 3 new cases announced by both Hong Kong and the WHO Western Pacific Regional Office this week. 

Ubiquitous in poultry across Asia and in much of the Middle East, LPAI H9N2 occasionally jumps to humans, generally producing only mild to moderate illness. 

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 those numbers would have us believe (see J. Infect & Public Health: High Seroprevalence Of Avian Influenza H9 Among Poultry Professionals In Pakistan)

You may recall in mid-January we saw a new case announced by China in a toddler from Guangdong Province, along with 6 previously unannounced cases from 2020 (link).  

The update from WHO WPRO follows, after which I'll have more on the potential threat posed by H9N2. 

Human infection with avian influenza A(H9N2) in China 

Three new cases of human infection with avian influenza A(H9N2) virus were reported to WHO, detected through influenza-like illness (ILI) surveillance. 

  • The first case is a one-year-old female from Sichuan Province, China, with onset of illness on 30 November 2020. The patient had exposure to backyard poultry. 
  • The second case is a five-year-old female in Anhui Province, China, whose date of onset was 17 January 2021
  • The third case is a 2-year-old female in Jiangxi Province, China whose date of onset was 18 January 2021.

All three cases had developed mild illness and recovered, and no additional cases suspected among contacts by the time of reporting. To date, five cases of avian influenza A(H9N2) were reported from China in 2021, and a total of 43 cases of human infection with avian influenza A(H9N2) in China have been reported since December 2015.

We've covered the growing risks from the avian H9N2 virus numerous times over the years, not only as a standalone virus (see Viruses: Characterization of the H9N2 Avian Influenza Viruses Currently Circulating in South China ), but also for its ability to reassort with other - potentially more dangerous - influenza subtypes (see Viruses: PA From Recent H9N2 AIV Enhances H5N1 Infection In Mammalian Systems).

In December of 2019, in EID Journal: Novel Reassortant HPAI A(H5N2) Virus in Broiler Chickens, Egypt, we saw a new proof of concept in the field, after an HPAI H5N8 virus reassorted with an LPAI H9N2 virus, and produced a new HPAI H5N2 virus in Egyptian poultry.

And 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].

While admittedly far less pathogenic in humans than many H5 and H7 subtypes, H9N2 raises pandemic concerns because it continues to evolve towards a more mammalian-adapted virus. 

Add in its legendary ability to reassort with other influenza subtypes, and it remains a virus to watch.