Thanks to China analyst David Cowhig for sending the following commentary into CDT:
The February 23 issue of the Economist mentions an article in the February 10, 2006 online edition of the Proceedings of the National Academy of Sciences (USA) that traces the spread of H5N1 after its establishment in southern China a decade ago by poultry transport and bird migration. The abstract is on the PNAS website.
The full article requires a subscription. Here is the abstract:
Establishment of multiple sublineages of H5N1 influenza virus in Asia: Implications for pandemic control
Preparedness for a possible influenza pandemic caused by highly pathogenic avian influenza A subtype H5N1 has become a global priority. The spread of the virus to Europe and continued human infection in Southeast Asia have heightened pandemic concern. It remains unknown from where the pandemic strain may emerge; current attention is directed at Vietnam, Thailand, and, more recently, Indonesia and China. Here, we report that genetically and antigenically distinct sublineages of H5N1 virus have become established in poultry in different geographical regions of Southeast Asia, indicating the long-term endemicity of the virus, and the isolation of H5N1 virus from apparently healthy migratory birds in southern China. Our data show that H5N1 influenza virus, has continued to spread from its established source in southern China to other regions through transport of poultry and bird migration. The identification of regionally distinct sublineages contributes to the understanding of the mechanism for the perpetuation and spread of H5N1, providing information that is directly relevant to control of the source of infection in poultry. It points to the necessity of surveillance that is geographically broader than previously supposed and that includes H5N1 viruses of greater genetic and antigenic diversity.
and the comment in the 2/23/06 Economist article:
A research paper in Proceedings of the National Academy of Sciences, published online on February 10th, shows that the H5N1 virus has persisted in its birthplace, southern China, for almost ten years and has been introduced into Vietnam on at least three occasions, and to Indonesia. The authors suggest that such transmissions are perpetuated mainly by the movement of poultry and poultry products, rather than by migrating birds.
This is significant because it strongly supports bird conservationists, who have been arguing that most outbreaks in South-East Asia can be linked to movements of poultry and poultry products, or infected material from poultry farms, such as mud on vehicles or people’s shoes. Conservationists also argue that live animal markets have played an important role in the H5N1‚Ä≤s spread. Such markets were the source of the first known outbreak in Hong Kong in 1997 when 20% of the chickens in live poultry markets were infected.
BirdLife International, a conservation group, reckons there are three likely transmission routes for H5N1: commercial trade and the movement of poultry; trade in wild birds; and the use of infected poultry manure as agricultural fertiliser. Bird conservationists add that although migratory birds can carry and transmit the virus, it is often not clear whether they picked up the infection from poultry.
In Nigeria, there is the suggestion that it was trade, and not migratory birds, that caused the outbreak. For one thing, the infection was first detected in a commercial farm with 46,000 poultry and not among backyard flocks which represent 60% of the country’s poultry production”and which would be expected to have greater contact with wild birds. ”
An October 2005 article in the Chinese economics and investigative reporting journal Caijing traced China’s attempts to grope with H5N1 under secrecy regulations and over the last several years more openly. A summary of the Caijing article is here.
The full text of a 2004 Proceedings of the National Academy of Sciences article on the evolution of H5N1 in ducks in China during 1999 – 2002 is available here.
