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Robert G. Webster, PhD
The H5N1 avian influenza virus continues to spread from its original source in southern China through transported poultry and bird migration. The virus has now established distinct subpopulations throughout Asia, according to investigators at St. Jude and several institutions in Asia.
The wide variety of H5N1 viruses represented by these subpopulations, or sub-lineages, challenges the wisdom of relying on a single virus to use as the basis of a human vaccine, the researchers said. A lineage is a group of viruses linked to each other by genetic descent from a common ancestor. A sub-lineage is an offshoot of such a line of viruses.
Instead of relying on a single virus, scientists should choose candidate viruses that reflect the diversity of H5N1 seen throughout Asia, central Asia and Turkey, the researchers said.
The genetic mutations that continually occur among these viruses demands that the choice of viruses to use for human vaccines must be continually updated. Therefore, scientists and public health officials must survey a much larger geographic area than previously thought in order to identify the early stages of an H5N1 pandemic.
A report on this study appears in the February 7 issue of Proceedings of the National Academy of Sciences.
Results of the study emphasize the importance of studying apparently healthy birds, since no outbreaks of disease occurred in any infected poultry in the regions studied, according to Robert G. Webster, PhD, Infectious Diseases, a co-author of the paper.
The recent spread of H5N1 throughout Asia and Turkey increases the threat that one of these sub-lineages could acquire the ability to spread among humans, Webster said. Currently, H5N1 is transmitted to humans through close contact with infected chickens. But if the virus acquires a mutation that enables it to pass directly from person to person like the annual human influenza does, the resulting pandemic could be disastrous.
“Our findings tell us that the best way to prevent such an outbreak is to control H5N1 at its source—domestic poultry in southern China,” Webster said. “Early detection of the virus and large-scale culling of infected poultry is one of the key strategies for controlling highly pathogenic strains of H5N1. Control measures have been less effective in China, Indonesia and Vietnam; and the problem that has allowed the virus to take root in those countries and repeatedly jump from poultry to other species, including humans, has not been solved.”
Last update: April 2006