#13,758
Almost 3 months ago, we looked at the The Multifaceted Zoonotic Risk of H9N2 Avian Influenza, an avian subtype that has been increasingly scrutinized for both its own pandemic potential, and for its contributions to the emergence of novel flu strains.
By itself, H9N2 produces mostly mild or moderate illness in humans, but its internal genes can be found in the backbone of many of the HPAI viruses (including H5N1, H5N6, and H7N9) that pose the greatest risks to both poultry, and human healthOver the past two decades, more than 3 dozen human H9N2 infections have been reported by just 3 countries - China, Pakistan & Egypt - (see FluTrackers Global Cumulative H9N2 Partial Case List 1998-2017), but seroprevalence studies of poultry workers where the virus is endemic suggest this is a significant under count.
While it may well be due to better testing and surveillance, we've seen a decided uptick in reported cases in the past 3 years. At the same time, we've seen the H9N2 virus acquire `mammalian adaptations' that could potentially increase its ability to infect humans.
In 2016's Genomic Characteristics Of 2 A(H9N2) Virus Isolates From Humans In Anhui Province - 2015, researchers found:
The amino acid sequence alignment results showed that several mutations for human infection tropism presented in the two virus strains, including Q226L, H183N and E190T in HA; S31N in M2; 63-65 deletion in NA. In addition, the H9N2 influenza virus strains possessed the PSRSSR\GL motif in HA.In 2015, in EID Journal: Replication Of Avian H9N2 In Pet Birds, Chickens, and Mammals, Bangladesh, scientists reported:
The H9N2 virus strain Env/9306 contains mammalian-like mutations in genes, including HAQ226L (H3 numbering) (5), which increase H9N2 virus transmissibility to and among mammals.And just over a year ago, in Three Mutations That Switch H7N9 To Human-type Receptor Specificity, G228S and Q226L were both called out at being instrumental in changing H7N9 into a more humanized virus.
As with all influenza subtypes - H9N2 describes a diverse and growing array of similar viruses - and not a single entity. The H9N2 viruses that circulate in Pakistan or Bangladesh are similar to - but are genetically distinct from - the H9N2 viruses that circulate in Korea, China, or Egypt.
This - along with other factors, including the use of PPEs by farm workers and the amount and quality of testing and surveillance - may account for why some countries have reported human cases, while others where the virus is endemic have not.Similarly, a 2014 seroprevalence study, found antibodies against H9N2 ranged from 5.9% to 7.5% among poultry exposed individuals in Egypt, while a 2016 PLoS One study found a seroprevalence in Southern China ranging from 1.37% to 3.42%.
Earlier this month, 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.
All of which brings us to a new open-access study, published this past week in the Journal of Infection & Public Health, which finds a remarkably high seroprevalance of H9 antibodies among poultry professionals in Pakistan.
Seroprevalence and risk factors of avian influenza H9 virus among poultry professionals in Rawalpindi, Pakistan.
Tahir MF1, Abbas MA2, Ghafoor T3, Dil S4, Shahid MA5, Bullo MMH6, Ain QU7, Ranjha MA8, Khan MA9, Naseem MT10.
Abstract
BACKGROUND:
Avian influenza H9 is endemic in commercial and backyard poultry in Pakistan and is a serious occupational health hazard to industry workers. This study aimed to determine the seroprevalence of avian influenza H9 infection in people working with poultry in Rawalpindi, Pakistan and assess the measures they took to protect themselves from infection.
METHODS:
A cross-sectional study was conducted from December 2016 to May 2017 of 419 people working with poultry in Rawalpindi Division, including farm workers, vaccinators, field veterinarians, butchers and staff working in diagnostic laboratories. Potential participants were randomly approached and gave written consent to participate. Data were collected using a standardized questionnaire and serum samples were processed to detect H9 antibodies using the haemagglutination inhibition test.
RESULTS:
Of the 419 participants, 406 (96.9%) were male. The mean age of the participants was 36.4 (SD 10.86) years. A total of 332 participants agreed to a blood test, 167 of whom were positive for A(H9) antibodies, giving an overall seroprevalence of 50.3%. Laboratory staff had the highest seroprevalence (100%) and veterinarians the lowest (38.5%).
Vaccinators, butchers and farm workers had a seroprevalence of 83.3%, 52.4% and 45.5% respectively. Personals who used facemasks had significantly lower (P < 0.002) seroprevalence (29.6%) than those who never used them (90.6%). Similarly, those who always used gloves and washed their hands with soap had a seroprevalence of 32.8% compared with 89.0% in those who never took these precautions. Of the participants who handled antigens, 92.3% were seropositive.
CONCLUSION:
Laboratory staff and vaccinators are exposed to viral cultures and influenza vaccines respectively which may explain their high seroprevalence.
Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved
These positive results are the highest I've seen by a large margin, and add to the concerns that H9N2 may be moving towards becoming a more `humanized' virus. The authors discuss some of the possible reasons behind these findings in their conclusion:
Serological evidence of human infection with A(H9N2) viruses has also been reported from neighboring countries of this region including India, China and Egypt [15], [16], [17], [18]. In these studies, the seroprevalence ranged between 1.2% and 17% in various categories of poultry professionals.
But in our study the seroprevalence of antibodies against A(H9N2) virus ranged from 38.5% to 100%.
The high seroprevalence might be attributed to an increased avian-to-human transmission capacity of the avian influenza virus in Pakistan through mutations and reassortments [19]. Similarly, the high seroprevalence in the vaccinators might be due to close contact with live birds during vaccination as well as poor compliance to PPE usage.
Overall the higher sero-prevalence may be due to the fact that vaccination against Influenza A(H9N2) is regularly used in poultry populations in Pakistan that may result in un-detected persistence of the pathogen facilitating its silent spread to other populations [20].
While we've witnessed a remarkable success over the past 18 months in China with their massive H5+H7 poultry vaccination program - poultry vaccination is not without some risk.
As avian viruses evolve, over time existing poultry vaccines can become less effective. Poor vaccine matches can then allow AI viruses to spread silently among flocks, to continue to reassort and evolve, and potentially lead to the emergence new subtypes of avian flu.A few earlier blogs on those concerns include:
Subclinical Highly Pathogenic Avian Influenza Virus Infection among Vaccinated Chickens, China).While H9N2 hasn't shown the sort of virulence in humans that we've seen with H5N1 or H7N9, it is regarded as having at least some pandemic potential (see CDC IRAT SCORE), and several candidate vaccines have been developed over the years.
Study: Recombinant H5N2 Avian Influenza Virus Strains In Vaccinated Chickens
EID Journal: Subclinical HPAI In Vaccinated Poultry – China
Add in its ability to reassort with other, potentially more virulence viruses, and H9N2 deserves both our attention, and our respect.
