A new study involving INRAE reveals the speed at which bird flu is spreading in live poultry markets in Asia. Scientists from the One Health Poultry Hub program have modeled the spread of avian flu in these markets, integrating for the first time biological data collected in the field. They focused their study on the H9N2 avian flu virus, which is not very virulent for poultry, but represents a major risk in the spread and evolution of the disease. Their results, published in Nature communications, show that 10% of birds arriving at markets are already contaminated, and over 90% of birds likely to be contaminated are infected within 24 hours at the market if they remain there for at least a day. They argue for the adoption of preventive measures upstream of markets by transporters and breeders to reduce the risk of the virus spreading, notably through vaccination strategies.
In Asia, live poultry markets are ubiquitous and very popular. They represent a strong cultural tradition where consumers personally select live birds. But they are also hotspots for the spread and evolution of avian flu viruses, as shown by a previous study by the One Health Poultry Hub program. The H9N2 avian flu virus is the most widespread in poultry farms. Although not very virulent in birds, it can be responsible for major production losses and represents a major economic risk for poultry farms. It can also be transmitted to humans, and has been implicated in the emergence of new avian flu variants such as the H5N1 virus. It therefore presents a potential pandemic risk.
This is why scientists have modeled the spread of this virus in live poultry markets, integrating for the first time biological field data from markets in Bangladesh. Their results show that :
- More than 9 out of 10 chickens entering the market without having been exposed to the H9N2 virus are infected within 24 hours if they remain there for at least a day.
- A bird infected with the virus can become contagious in less than 5 hours 30 minutes.
- 1 bird in 10 arrives at the market already infected.
The model developed enables scientists to go a step further and assess the impact of potential sanitary measures to reduce the prevalence of the H9N2 virus in live markets.
Currently, veterinary public health interventions to limit the spread of the virus focus on the markets themselves. These include prohibiting the keeping of birds in markets overnight, reinforcing "non-working days" in markets, and separating the different bird species present. However, the results of the study show that these measures are unlikely to be effective in reducing the risk of human exposure to the virus if they are not complemented by measures implemented throughout the market supply chain. Pandemic prevention strategies must therefore also target poultry farms and transporters in countries where the virus is endemic, in order to reduce the number of infected birds entering markets. In particular, their results argue in favor of multi-faceted interventions, including vaccination strategies for birds destined for live poultry markets.
The new insights provided by this study will be incorporated into the EPINEST computer model, the first computerized tool developed by the One Health Poultry program to monitor viruses and bacteria on farms.
One Health Poultry Hub is an interdisciplinary research and development program working to meet the growing demand for poultry meat and eggs in Asia while minimizing public health risks. The program brings together laboratory, clinical research, veterinary and social scientists from 27 institutions in 10 countries adopting a One Health approach to providing healthy, sustainable food. Launched in 2019, One Health Poultry Hub is running projects in Bangladesh, India, Sri lanka and Vietnam. https://www.onehealthpoultry.org/
The program is funded by the UK’s Global Challenge Research Fund (GCRF).
Avian flu: a disease caused by different viruses
Avian flu viruses belong to type A. Type A viruses are characterized by the protein subtypes of 2 surface proteins, hemaglutinin (H) and neuraminidase (N). 16 subtypes of H, 9 of N, with all possible combinations, are present in wild birds, their reservoir.
When these viruses infect poultry, some can become highly virulent in poultry, as in the case of H5N1.
Several viral subtypes of avian flu are zoonotic. See below:
The main avian influenza subtypes causing human cases (please note that numbers correspond to cases reported in the WHO Asia-Pacific region)
https://www.who.int/westernpacific/wpro-emergencies/surveillance/avian-influenza
Recent human case of H9N2
https://www.who.int/emergencies/disease-outbreak-news/item/2024-DON514
Reference
Francesco Pinotti et al . Modelling the transmission dynamics of H9N2 avian influenza viruses in a live bird market, Nature Communications (2024) DOI: https://doi.org/10.1038/s41467’024 -47703-9
The study includes scientists from the Royal Veterinary College and Oxford University in the UK, City University of Hong Kong in China, Chittagong University of Veterinary and Animal Sciences in Bangladesh, and INRAE.
