Since it was identified in 1996, one strain of avian influenza (H5N1) has spread to more than 60 countries with a human fatality rate of 50-60 per cent. A new study shows the virus tended to move between nearby provinces especially where there was intense live poultry trade. The same trend was found in two other strains of avian influenza: H7N9 and H5N6.
The SMC asked experts to comment on the research
Professor David Hayman, Professor of Infectious Disease Ecology, Massey University School of Veterinary Science, comments
"This is an important paper that uses genetic and animal production data to determine that the transmission of highly pathogenic avian influenza A viruses, aka 'bird flu', in China, which can infect and kill people, are driven largely by national-level poultry trade networks. The results suggest this is true for all three major avian influenza virus lineages in poultry in the country.
"This work suggests that the control of these viruses, therefore, is dependent on poultry production rather than wild birds. This means that while evidence suggests wild birds maintain these viruses in nature, people can limit the disease potential through poultry management, which is easier than attempting to intervene with wild bird systems."
No conflict of interest.
Professor Robert G. Webster, Department of Infectious Diseases, St. Jude Children's Research Hospital, USA, comments
"This is an extremely timely paper by an international consortium of scientists from multiple centers in China, United Kingdom, Norway, Belgium and the United States on the role of live poultry markets in the spread of multiple subtypes of H5 avian influenza viruses. While the H5N1, H7N9 and H5N6 avian influenza viruses have not yet learned to transmit human-to-human they do have pandemic potential.
"This paper provides strong evidence for the role of the poultry trade network in the spread of these three H5 genotypes and considers the role of wild bird migration for long distance spread. There is a still a paucity of sequence data on influenza viruses from wild birds outside of Hong Kong and Qinghai Lake on which to base analysis of long distance spread.
"The paper deals with prevention and control efforts to disrupt the spread of influenza viruses between source and sink locations. While understanding the spread of H5 influenza viruses is essential for control an even more important strategy is to prevent the emergence of these viruses in live poultry markets by permanently closing such markets.
"The emergence of H5 influenza viruses, of SARS, of the new coronavirus (COVID-19) have been traced to live animal markets. China is now a wealthy country that could phase out such markets particularly the exotic animal markets."
No conflict of interest.
Dr Joanna McKenzie, One Health epidemiologist, School of Veterinary Science, Massey University, comments
“This paper is interesting not so much for the authors’ findings, which are consistent with existing knowledge on transmission of the different clades of avian influenza viruses, but for its underlying demonstration of the value of:
- Good quality data on live poultry trade networks and migratory bird movement, and
- Good quality data on the distribution of outbreaks and the genomic sequence of avian influenza viruses (or any pathogenic organism) associated with each outbreak.
"Understanding poultry trade networks helps to prepare for and respond more quickly to the introduction or emergence of pathogenic organisms (including viruses, antimicrobial resistant bacteria, etc) in poultry. It identifies major poultry trade networks (described in the paper as live poultry trade communities) plus hubs that link the different networks.
"Some hubs act as a major source of poultry for the different communities, i.e. areas that have a high density of poultry production and supply a high proportion of birds to other areas. Some hubs have a higher probability of receiving poultry from the different networks and thus may have a higher risk of virus arriving in the area.
"Having knowledge of these hubs, provides the opportunity to target surveillance to detect outbreaks of known diseases such as avian influenza plus to detect new and unusual diseases in these areas, referred to as risk-based surveillance.
"Good quality outbreak data, particularly good geographic coverage of outbreaks and consistent coverage over time, enables an understanding of the distribution of outbreaks. Genetic analysis of viruses associated with the outbreaks is essential to understand the distribution of specific genetic clades geographically and over time.
"The important message for me from this paper is the importance of having good surveillance systems in place to detect and investigate disease outbreaks, record details of the outbreak, conduct genetic analysis of the pathogens, and to report the findings nationally. This is important for detecting and monitoring zoonotic diseases in animals and/or people and understanding the public health risks of the outbreaks.
"It is important to be careful not to make inferences that avian influenza has any link with COVID-19! The only link is that they are both zoonotic diseases but they are extremely different diseases."
No conflict of interest.