Thursday, March 09, 2017

Emerg. Microbes: Dynamics Of Transmission Of H5N1 & H9N2 In Live Bird Markets - Bangladesh


The link between exposure to poultry at live bird markets and infection by avian flu is well established. In the summer of 2014, in CDC: Risk Factors Involved With H7N9 Infection we looked at a case-control study conducted by an international group of scientists, including researchers from both the Chinese and the US CDC which concluded.
Exposures to poultry in markets were associated with A(H7N9) virus infection, even without poultry contact. China should consider permanently closing live poultry markets or aggressively pursuing control measures to prevent spread of this emerging pathogen. 
In October of 2013 we saw another study (see The Lancet: Poultry Market Closure Effect On H7N9 Transmission) which found that `closure of LPMs reduced the mean daily number of infections by 99%'.

Less well understood (although strongly suspected) are the impacts of housing multiple bird species, brought in from different regions, in the tight quarters of poultry markets on the evolution of novel flu viruses.

The bringing together of water fowl (ducks, geese), with poultry and other terrestrial birds (e.g. chickens, quail) provides ample opportunities for the mixing and matching of flu viruses through reassortment. 

Many of the novel flu viruses that have emerged over the past two decades share internal genes with a low path, yet highly ubiquitous poultry virus (H9N2).
All of which makes  Bangladesh an ideal place to study the dynamics and evolution of avian flu viruses in live bird markets (LBMs). 

Yesterday an international team of researchers (including Robert G. Webster & Richard J. Webby) published a detailed study which finds the prevalence of avian flu three times higher in LBMs than in local farms, and highlights the dangers of intermixing avian species.

Due to its length I've only included the abstract and a couple of snippets from the discussion. Follow the link below, as the full (open access) report is well worth reading in its entirety.

Citation: Emerging Microbes & Infections (2017) 6, e12; doi:10.1038/emi.2016.142

Published online 8 March 2017

Insight into live bird markets of Bangladesh: an overview of the dynamics of transmission of H5N1 and H9N2 avian influenza viruses

Jasmine C M Turner1, Mohammed M Feeroz2, M Kamrul Hasan3, Sharmin Akhtar3, David Walker1, Patrick Seiler1, Subrata Barman1, John Franks1, Lisa Jones-Engel3, Pamela McKenzie1, Scott Krauss1, Richard J Webby1, Ghazi Kayali4,5 and Robert G Webster1

Correspondence: G Kayali, E-mail:; RG Webster, E-mail:

Received 26 October 2016; Revised 20 December 2016; Accepted 26 December 2016


Highly pathogenic avian influenza (HPAI) H5N1 and low pathogenic avian influenza (LPAI) H9N2 viruses have been recognized as threats to public health in Bangladesh since 2007. Although live bird markets (LBMs) have been implicated in the transmission, dissemination, and circulation of these viruses, an in-depth analysis of the dynamics of avian transmission of H5N1 and H9N2 viruses at the human–animal interface has been lacking. Here we present and evaluate epidemiological findings from active surveillance conducted among poultry in various production sectors in Bangladesh from 2008 to 2016.

Overall, the prevalence of avian influenza viruses (AIVs) in collected samples was 24%. Our data show that AIVs are more prevalent in domestic birds within LBMs (30.4%) than in farms (9.6%). Quail, chickens and ducks showed a high prevalence of AIVs (>20%). The vast majority of AIVs detected (99.7%) have come from apparently healthy birds and poultry drinking water served as a reservoir of AIVs with a prevalence of 32.5% in collected samples. HPAI H5N1 was more frequently detected in ducks while H9N2 was more common in chickens and quail. LBMs, particularly wholesale markets, have become a potential reservoir for various types of AIVs, including HPAI H5N1 and LPAI H9N2. 

The persistence of AIVs in LBMs is of great concern to public health, and this study highlights the importance of regularly reviewing and implementing infection control procedures as a means of reducing the exposure of the general public to AIVs.

The presence of H5N1 and co-infections of H5/H9, along with non-H5/H9 viruses, in wholesale markets raises concern for public health. The data presented show that ducks are the primary species for H5N1, H5/H9 co-infections and non-H5-H9 infections suggesting within the LBMs, ducks are the potential reservoirs for reassortment events to take place.

Previous studies7, 12 have shown that H9N2 viruses isolated from Bangladesh are reassortant viruses, possessing the nonstructural (NS), and polymerase PA and PB1 genes, from an H7N3 virus from Pakistan. H9N2 viruses donated their internal genes to several H5 and H7 viruses of public health concern.22 It has also been previously shown12 that chicken H9N2 in Bangladesh is antigenically conserved compared to quail H9N2 which shows antigenic drift. H9N2 viruses tend to evolve rapidly and acquire mutations that confer replication in mammalian hosts, much like H5N1 isolated from Bangladesh.12
(Continue . . . )

While not the only driver of avian flu's evolution, LBMs provide a particularly hospitable environment, and enhanced opportunities, for novel influenza viruses to evolve and adapt to new host species. 

No comments: