#16,335
LPAI (low pathogenic avian influenza) H9N2 is ubiquitous in poultry across much of Asia, Russia, the Middle East, and in recent years, parts of central Africa. Unlike the more virulent H5 and H7 avian viruses, it is not considered a `reportable' disease by the OIE, and so our understanding of its range, and continued spread, is limited.
While human infection with H9N2 has only rarely been reported (< 100 cases), it is almost certainly happens more often than we know (see J. Infect & Public Health: High Seroprevalence Of Avian Influenza H9 Among Poultry Professionals In Pakistan).
Most human infections are mild, and occur in regions of the world where medical care - particularly for mild viral illnesses - is rarely sought. And even when it is, testing for H9N2 is rarely performed.
In May of 2020, the CDC added a new lineage (H9N2 Y280 lineage [A/Anhui-Lujiang/13/2018]) to their short list of novel flu viruses with at least some pandemic potential, although it would not be expected to gave the same impact as an H5 or H7 avian flu.
But H9N2's greatest claim to fame it its ability to reassort with other - sometimes far more worrisome - viruses. Often, when new HPAI flu strains emerge – if you look deep enough – you’ll find LPAI H9N2 was part of the process (see PNAS: Evolution Of H9N2 And It’s Effect On The Genesis Of H7N9).
Three years ago, in EID Journal: Two H9N2 Studies Of Note, we looked at two reports which suggest 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.
Yesterday, in the ECDC's COMMUNICABLE DISEASE THREATS REPORT for Week 46, 14-20 November 2021, a recent, and rare fatal infection with H9N2 was announced out of China.
Influenza A(H9N2) - Multi-country (World)
Monitoring human cases Opening date: 30 January 2019 Latest update: 19 November 2021
Epidemiological summary
As of 16 November 2021, and since the previous monthly report published in CDTR on 18 October 2021, one new case of human infection with avian influenza A(H9N2) was reported from China. The case is a 39-year-old male from Qiandongnan Autonomous Prefecture, Guizhou Prefecture. The case developed symptoms on 29 October 2021 and was hospitalised the same day with severe condition. He died on 1 November 2021.
Summary: As of 16 November 2021 and since 1998, a total of 94 laboratory-confirmed cases of human infection with avian influenza A(H9N2) viruses have been reported, from China (82), Egypt (4), Bangladesh (3), Cambodia (1), Oman (1), Pakistan (1), India (1), and Senegal (1). Most of the cases were children with mild disease.
Sources: ECDC avian influenza page | Joint ECDC, EFSA and EU Reference Laboratory scientific for avian influenza report: Avian influenza overview May ±August 2020 | WHO IHR
ECDC assessment
Sporadic human cases of avian influenza A(H9N2) have been previously observed. No human-to-human transmission has been reported. Sporadic zoonotic transmission cannot be excluded; the use of personal protective measures for people directly exposed to potentially infected poultry and birds with avian influenza viruses will minimise the remaining risk. The risk of zoonotic influenza transmission to the general public in EU/EEA countries is considered to be very low.
Actions
ECDC monitors avian influenza strains through its epidemic intelligence activities in order to identify significant changes in the epidemiology of the virus. ECDC, together with EFSA and the EU reference laboratory for avian influenza, produces a quarterly updated report on the avian influenza situation. The most recent report was published on 30 September 2021 and the next will be published 21 December 2021.
Since we have no information on the patient beyond the gender and age, it is unknown what - if any - comorbidities may have contributed to this patient's death. While death is a rare outcome with H9N2, any flu virus has the potential to be lethal under the right conditions.
Hopefully additional details on this case will be published by Chinese researchers.
