Avian influenza viruses bind preferentially to the α2-3 receptor cells that are most commonly found in the gastrointestinal tract of aquatic birds, and is believed mostly spread via infected feces.
For that reason researchers have concentrated less on airborne spread among birds, and more on fomites and shared water sources.Recently, however, we've seen renewed interest in aerosolized avian flu - particularly in and around Live Poultry Markets (LPMs) - where birds are housed, slaughtered, and sometimes mechanically defeathered for the customer (see How to Aerosolize A Chicken).
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 visiting LPMs as the prime risk factor for infection. Since then we've seen cases whose likely exposures was cited as simply living near, or walking past an LPM.
A little over a year ago, in Detection Of Airborne H9 Nucleic Acid In Chinese Live Poultry Market, we looked at an article appearing in the Chinese Medical Journal which found ample environmental evidence of viral contamination, and reports the first positive detection of Airborne H9 (presumably H9N2) in a Chinese LPM.
Samples were cataloged and tested for influenza A viral RNA and positive samples were then analyzed to determine their (H5/H7/H9) subtype. This detection of viral RNA is a much lower bar than isolating a live virus, and doesn't tell us about the viability of the viruses they detected.That study found ample environmental evidence of viral contamination, and reports the first positive detection of Airborne H9 (presumably H9N2) in a Chinese LPM. Another study - published last August - found similar results with the H5N6 virus (see J. Infection: Aerosolized H5N6 At A Chinese LBM (Live Bird Market))
Today we've a new report, again on avian H9N2, only this time they managed to isolate and sequence one of these airborne viruses.
Avian influenza H9N2 virus isolated from air samples in LPMs in Jiangxi, China
Xiaoxu Zeng†,Mingbin Liu†,Heng Zhang,Jingwen Wu,Xiang Zhao,Wenbing Chen,Lei Yang, Fenglan He,Guoyin Fan,Dayan Wang,Haiying Chen and Yuelong Shu †Contributed equally
© The Author(s). 2017
Published: 24 July 2017
Recently, avian influenza virus has caused repeated worldwide outbreaks in humans. Live Poultry Markets (LPMs) play an important role in the circulation and reassortment of novel Avian Influenza Virus (AIVs). Aerosol transmission is one of the most important pathways for influenza virus to spread among poultry, from poultry to mammals, and among mammals.
In this study, air samples were collected from LPMs in Nanchang city between April 2014 and March 2015 to investigate possible aerosol transmission of AIVs. Air samples were detected for Flu A by Real-Time Reverse Transcription-Polymerase Chain Reaction (RRT-PCR). If samples were positive for Flu A, they were inoculated into 9- to 10-day-old specific-pathogen-free embryonated eggs. If the result was positive, the whole genome of the virus was sequenced by MiSeq. Phylogenetic trees of all 8 segments were constructed using MEGA 6.05 software.
To investigate the possible aerosol transmission of AIVs, 807 air samples were collected from LPMs in Nanchang city between April 2014 and March 2015. Based on RRT-PCR results, 275 samples (34.1%) were Flu A positive, and one virus was successfully isolated with embryonated eggs. The virus shared high nucleotide homology with H9N2 AIVs from South China.
Conclusions(Continue . . . .)
Our study provides further evidence that the air in LPMs can be contaminated by influenza viruses and their nucleic acids, and this should be considered when choosing and evaluating disinfection strategies in LPMs, such as regular air disinfection. Aerosolized viruses such as the H9N2 virus detected in this study can increase the risk of human infection when people are exposed in LPMs.
A bit more controversial, we've also seen some evidence suggesting avian influenza viruses can be spread from farm to farm - at least over short distances - by prevailing winds (see Bird Flu’s Airborne `Division).
Just over two years ago, in CIDRAP: H5N2 Roundup & Detection In Environmental Air Samples, we looked at testing conducted by the University of Minnesota around infected poultry farms also that found evidence of airborne virus particles.
The science of all of this even has a name; aerobiology – the study of how bacteria, fungal spores, pollen and even viruses can be passively transported in the air.The evidence of short-distance airborne spread of avian viruses in LPMs grows stronger each year, and reinforces the need to better control - or even shut down - these live markets. For more on the threat posed by LPMs, you may wish to revisit: