Who’s responsible for the spread of H7N9 influenza virus in a live animal market?

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Limited transmission in a simulated live animal market

Text by Angela Bosco-Lauth

Influenza viruses can cause serious disease in humans and are often harbored by domestic birds, including chickens and ducks.  It is believed that the H7N9 strain of influenza can be spread to people by contact with poultry in live animal markets.  In our study, we looked at transmission of the H7N9 influenza virus between chickens and other birds in adjacent cages to try to better understand how the virus is spread between animals and potentially to people in a live animal market setting.  To do so, we used stacking cages and varied the orientation of the following species: chickens, pigeons, pheasants, quail, sparrows and cottontail rabbits.  We also included free-ranging sparrows and pigeons in the room.  We found that, when in the top cage, infected chickens were able to spread the virus to quail in the cage below, but no other animals, including other chickens, developed infections.

The idea for this study came from curiosity about how influenza viruses, such as H7N9, can be transmitted in a live animal market setting.  We were quite surprised when we discovered that infected chickens didn’t shed large amounts of virus or transmit to uninfected cage mates.  Instead, the quail in the cage below the infected chickens acquired H7N9 infections and shed more virus for a longer duration.   This leads us to believe that this particular strain of influenza is not likely spread as efficiently by chickens as some other strains of influenza, but could very well be spread by quail or other animals that have not been investigated at this point.  Interestingly, other species (pigeons, sparrows, pheasants, and cottontails) in the cages near the quail did not become infected, even though we know that they can be experimentally infected and shed the virus.  Also, neither the quail in cages above infected chickens nor free-ranging birds became infected.  All together, this leads us to believe that the spread of the H7N9 virus is not likely due to aerosol droplets.  Thus, the actual position of animals in cages relative to one another may be a contributing factor in virus transmission, and we need to be conscious of the fact that limited transmission between and among a variety of species of birds in a wet market setting likely contributes to the presence and spread of H7N9 influenza to humans.

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This photo was taken during the artificial wet market study to illustrate how the cages were set up and the access to cages by free-ranging pigeons and sparrows.

Introducing the author

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Angela Bosco-Lauth

About the research

Limited transmission of emergent H7N9 influenza A virus in a simulated live animal market: Do chickens pose the principal transmission threat?

Angela M. Bosco-Lauth, Richard A. Bowen, J. Jeffrey Root

Virology, Volume 495, August 2016, Pages 161–166