New modelling of a live market in Vietnam has determined that the best way to stop the transmission of avian influenza H7N9 (bird flu) in live markets is to ban overnight stays and deploy portable testing equipment.
Research funded by the United States Agency for International Development (USAID) and the FEDER/Région Occitanie Recherche et Sociétés has found that rapid detection of emerging virus is critical given the ‘sharp increase’ of H7N9 outbreaks in China between 2013-2017. This has broader regional public health and economic implications for countries such as Vietnam with the cross-border trade of birds coming from China.
“In Chinese live bird markets, H7N9 virus has been extensively detected in chickens, which are the primary source of H7N9 infection in humans. Frequent interactions among different poultry species and humans at live bird markets provide an ideal interface for transmission of AIV and emergence of new variants by mixing AIV from different sources,” the paper says.
By improving traditional surveillance and testing methods at live bird markets the risk of infecting humans with avian influenza viruses can also be reduced in more cost effective and timely ways, the researchers say. They noted that the introduction of a portable PCR device to test animals at a live market in Giê ́ng Vuông, Vietnam, allowed for virus detection within seven hours of sampling, compared with the 72 hour result if undertaken in a laboratory setting.
“The current surveillance programme for H7N9 in Vietnam involved biweekly random sampling of chickens in live bird markets with value chain linkages to China,” the paper says.
“All samples were transported to an official diagnostic laboratory where they were consecutively screened for M, H7 and N9 genes using RT-PCR. As an alternative to this surveillance strategy, a portable PCR device has been introduced recently to improve H7N9 detection and response capacities in Vietnam.”
Using a transmission model to improve surveillance at a live market, results show that ‘banning birds staying overnight would [also] represent an effective intervention to reduce the risk of H7N9 spread’. One obvious challenge to adequate bird monitoring is the frequency of poultry turn-over in live markets.
“Birds infected with H7N9 generally show mild clinical signs but they can excrete the virus for five to eight days,” the researchers say.
“Traders [in a North Vietnamese market] reported keeping birds for a few days within the live bird market until being sold, housing them in cages overnight. These birds staying for a longer time at [the market] are more likely to get infected and play an important role in the maintenance and amplification of H7N9 within the live bird market.”
The study was published on Wednesday and led by Dr Claire Guinat from the Université de Toulouse.
According to the study, beyond banning the housing of poultry overnight, two key measures can curb the transmission of bird flu in live markets: testing for the low pathogenic virus with a portable diagnostic device; and sampling any bird that is kept the market.
“These strategies should receive high priority […] Asian countries at risk of H7N9 introduction,” the paper reads.