New Bird Flu Virus Spreads Across Southeast Asia

MEMPHIS, Tennessee, November 1, 2006 (ENS) - A new variant of the bird flu virus H5N1 that arose in southern China late last year appears to be responsible for the increased occurrence of H5N1 poultry infections, as well as recent human cases in China, according to researchers at the University of Hong Kong in collaboration with scientists at St. Jude Children’s Research Hospital in Memphis.

The previously unknown virus is a sub-lineage of H5N1 avian influenza virus that has caused the deaths of more than 200 million poultry and 152 humans in 10 countries since December 2003.

Most human deaths in this period have occurred when people have come into close contact with infected poultry.

chicken

Indonesian health workers vaccinate a chicken against bird flu. (Photo by A. Ariadi courtesy FAO)
Identification of the new sub-lineage is significant, scientists say, because H5N1 is the most likely virus to trigger a worldwide human influenza pandemic if it mutates into a form that spreads easily from person to person.

The new virus, called Fujian-like, FL, has now been transmitted to Hong Kong, Laos, Malaysia, and Thailand, resulting in a new bird flu outbreak wave in Southeast Asia that has caused human infections as well, according to the Hong Kong/St. Jude team.

Their study, published in the current issue of the Proceedings of the National Academy of Science, warns that the H5N1 virus has not been contained, despite an ongoing program to vaccinate poultry.

"The development of highly pathogenic avian H5N1 influenza viruses in poultry in Eurasia accompanied with the increase in human infection in 2006 suggests that the virus has not been effectively contained and that the pandemic threat persists," the study states.

The increasing number of transmissions from birds to humans in the past year supports this opinion, said Robert Webster, PhD, a co-author of the paper and a member of the Infectious Diseases department at St. Jude.

Webster

Robert Webster is a member of the St. Jude faculty. Dr. Webster's interests include the structure and function of influenza virus proteins and the development of new vaccines and antivirals. (Photo courtesy St. Jude)
Based on their study of vaccinated poultry, the Hong Kong/St. Jude team suggested that the vaccination itself might have facilitated emergence of this new variant.

This appearance and rapid distribution of FL, despite the vaccination program that was started in September 2005, also suggests that the current H5N1 control measures are still inadequate, Webster said.

Since November 2005, the study found, some of the 22 H5N1 human infections reported from 14 provinces in China were from infected residents of metropolitan areas such as Shangai, Wuhan and Guangzhou, which are remote from poultry farms.

“We don’t know yet whether the people in those metropolitan areas were infected locally by contact with poultry or by contact with other humans,” Webster said, “but we suspect from the studies they are being infected by contact with poultry.”

The investigators also warned that it is possible that this new H5N1 variant will spread further through Asia and into Europe, as it evolves to form other sublineages that vary from place to place. This evolution into different sublineages also occurred during the previous two waves of H5N1 transmission that occurred during the past several years, they said.

While this discovery may increase fears of a pandemic, Professor Yi Guan of the University of Hong Kong, leader of the large team of investigators on the study, said a pandemic might not occur as a result of the emergence of the FL sub-lineage.

Yi

Virologist Yi Guan of the University of Hong Kong led the study team that discovered the new H5N1 sub-lineage. (Photo courtesy University of Hong Kong Li Ka Shing Faculty of Medicine)
"We have no information to suggest that this is more highly pathogenic or that this virus is a more likely candidate for a pandemic virus than any other H5N1 or other subtype virus," the virologist told "The Daily Telegraph."

Still, the investigators also conducted genetic studies of 390 H5N1 viruses isolated from poultry in the current study and found that 68 percent were of the FL sublineage.

The emergence of FL-like viruses and their success in replacing other H5N1 variants in such a short time demonstrates how difficult it is to control H5N1 in China, Webster said.

In their study, the authors wrote, "The predominance of this virus over a large geographical region within a short period directly challenges current disease control measures."

This research was supported in part by the Li Ka Shing Foundation, the U.S. National Institute of Allergy and Infectious Diseases and the American Lebanese Syrian Associated Charities, ALSAC.

ALSAC is the third largest healthcare related charity in the United States, and it has been the exclusive fundraising organization of St. Jude Children's Research Hospital since 1957.