#18,195
While the world battles the meteoric rise of HPAI H5 clade 2.3.4.4b - most famously now infecting American Dairy cows - the conditions which sparked the generation, evolution, and eventual spread of that specific H5 avian flu virus continue to thrive around the globe.
Live bird markets (LBMs) - which are ubiquitous across much of Asia - bring together many different types of birds (chickens, ducks, geese, quail, etc.) - often from distant farms - many of which carry diverse influenza subtypes.
When a single host (bird, pig, human, etc.) is infected by two different influenza A viruses, they can reassort into a new subtype or genotype. This ability to swap out interchangeable genetic parts is what makes LBMs (and mixed-species farms) so dangerous.
Birds are slaughtered (and often mechanically de-feathered) in open air booths as thousands of people walk by.
Several studies have isolated HPAI and LPAI virus in the ambient air, including Zoonoses & Public Health: Aerosol Exposure of Live Bird Market Workers to Viable Influenza A/H5N1 and A/H9N2 Viruses, Cambodia.
In 2014, a year after the H7N9 virus emerged in China, in CDC: Risk Factors Involved With H7N9 Infection, we looked at a case-control study that pretty much nailed LPMs as the prime risk factor for infection.
While even casual exposure to poultry in live bird markets was cited as the primary risk factor, people who owned, raised, or slaughtered birds at home, on farms, or in the wild were not found to be at any increased risk.
Legal markets can at least be inspected and regulated. Which is why LBMs are still tolerated in many countries and most bans have been short-lived.
Vietnam, which has recently seen a resurgence in human spillovers of HPAI and LPAI avian flu (see here & here) and the appearance of a new Reassortment Between H5N1 Clade 2.3.4.4b & Clade 2.3.2.1c Viruses In Mekong Delta Region, has many large LBMs.
Today we've the results of a monthly survey of 4 LBMs over 2019-2021, which finds `high prevalences of avian influenza A viruses' in these markets, and warns of the risks of future incursions of new subtypes from China.
High Prevalence of Highly Pathogenic Avian Influenza: A Virus in Vietnam's Live Bird Markets
Duy Tung Dao, Kristen K Coleman, Vuong N Bui, Anh N Bui, Long H Tran, Quy D Nguyen, Son Than, Laura A Pulscher, Lyudmyla V Marushchak, Emily R Robie ... Show more
Open Forum Infectious Diseases, Volume 11, Issue 7, July 2024, ofae355, https://doi.org/10.1093/ofid/ofae355
Published: 11 July 2024
Background
Background
In recent years, Vietnam has suffered multiple epizootics of influenza in poultry.
Methods
From 10 January 2019 to 26 April 2021, we employed a One Health influenza surveillance approach at live bird markets (LBMs) and swine farms in Northern Vietnam. When the COVID-19 pandemic permitted, each month, field teams collected oral secretion samples from poultry and pigs, animal facility bioaerosol and fecal samples, and animal worker nasal washes at 4 LBMs and 5 swine farms across 5 sites. Initially samples were screened with molecular assays followed by culture in embryonated eggs (poultry swabs) or Madin-Darby canine kidney cells (human or swine swabs).
Results
Many of the 3493 samples collected had either molecular or culture evidence for influenza A virus, including 314 (37.5%) of the 837 poultry oropharyngeal swabs, 144 (25.1%) of the 574 bioaerosol samples, 438 (34.9%) of the 1257 poultry fecal swab samples, and 16 (1.9%) of the 828 human nasal washes. Culturing poultry samples yielded 454 influenza A isolates, 83 of which were H5, and 70 (84.3%) of these were highly pathogenic. Additionally, a positive human sample had a H9N2 avian-like PB1 gene. In contrast, the prevalence of influenza A in the swine farms was much lower with only 6 (0.4%) of the 1700 total swine farm samples studied, having molecular evidence for influenza A virus.
Conclusions
This study suggests that Vietnam's LBMs continue to harbor high prevalences of avian influenza A viruses, including many highly pathogenic H5N6 strains, which will continue to threaten poultry and humans.
(SNIP)
DISCUSSION
The main objective of this study was to conduct surveillance for influenza A viruses among LBMs and swine farms in Northern Vietnam, with a specific focus on possible novel virus introductions from China. Evidence for such China-to-Vietnam influenza virus incursions have been reported for avian H5N1, H5N6, H6, and H9 strains [16–18].
Because avian influenza was known to be prevalent among Vietnamese poultry before our study, further novel virus introductions from China, such as H7N9 strains, could mix with Vietnamese strains and threaten poultry, yielding additional novel and virulent strains that might further threaten Vietnamese poultry and humans. Hence, we sampled geographical areas where viruses from China might enter Vietnamese agriculture. Fortunately, we did not find evidence of H7N9 or other viral incursions from China.
Even so, we compared to our previous studies [5, 6, 19–22], the LBM sites had surprisingly high prevalence estimates for influenza A positivity, and notably for highly pathogenic H5 subtypes. These findings were not totally surprising as highly pathogenic H5 subtypes have been circulating in Vietnam for approximately 20 years [23].
Interestingly, some of the H5-positive samples submitted for NGS identified subtypes other than H5. Although the reason for the discrepancy between the qRT-PCR and NGS results is not fully known, such discrepancies have previously been noted and may be due to quality of the RNA or coverage and depth of the NGS reads [24, 25]. Our surveillance findings were not reported to be associated with unusual morbidity in LBMs, suggesting that high HPAI prevalence in Vietnamese LBM maybe normative.
Through this surveillance, we also demonstrated that small teams of field workers are capable of conducting monthly sampling visits using a comprehensive One Health approach that could provide local and national public health and domestic animal production officials’ rapid feedback regarding “hot spot” locations and animal specimen types with concerningly high rates of influenza A positivity.
(SNIP)
Although we cannot ascertain what the influenza subtype was, a previous longitudinal cohort study found a 9% seroconversion rate to avian influenza H9 among Vietnamese farming households [32], suggesting infections among LBM workers may be occurring. Indeed, molecular and serological evidence of avian influenza H9N2 among poultry workers has been previously reported [33]. Furthermore, bioaerosol sampling appears to be a sufficient influenza virus surveillance tool that could potentially replace more invasive bird swab sampling.
Such environmental sampling is relatively easy to use, highly portable, nonintrusive, and generally well accepted by market workers, making this surveillance tool a great alternative to the traditional methods of individual sampling of animals. Results from this study can inform future avian influenza surveillance and control efforts in rural and remote locations similar to the sampling sites in this study.
A reminder that any victories we enjoy against HPAI H5 are apt to be fleeting - since we continue to monitor a growing array of recently emerged avian and swine flu threats - some of which could prove every bit as daunting as H5N1.
A few recent blogs include:
Frontiers: Phylogenetic and Mutational Analysis of H10N3 Avian Influenza A virus in China: Potential Threats to Human Health
Cambodia Reports 7th H5N1 Case of 2024
WHO WPRO Reports 2nd H5N6 Case In Fujian, China In 2024
Chinese CDC: A Retrospective Investigation of a Case of Dual Infection by Avian A (H10N5) and Seasonal Influenza A (H3N2) Viruses
Nature Comms: Potential Pandemic Risk of Circulating Swine H1N2 Influenza Viruses
WHO: India Reports 2nd H9N2 Case
