2006-01-13-Turkey's Bird Flu Virus May Be More Infectious StrainUnderstanding Avian Influenza
2006-01-13-Turkey's Bird Flu Virus May Be More Infectious Strain
Turkey's strain of the H5N1 bird flu that has infected at least 18 people may be a mutation of the virus sickening people in Asia and may be more capable of infecting humans, the World Health Organization said.
Samples from one patient who died of avian influenza in Turkey showed mutations where the virus binds to human cells, the WHO said on its Web site yesterday, citing an analysis at the MRC National Institute for Medical Research in Mill Hill, London. One of the mutations was seen previously in viruses isolated from an outbreak in Hong Kong in 2003 and from a 2005 outbreak in Vietnam.
``The Hong Kong 2003 viruses bind preferentially to human cell receptors more so than to avian cell receptors,'' the WHO said in its statement. Mill Hill researchers ``anticipate that the Turkish virus will also have this characteristic.''
The finding increases the need to control outbreaks of H5N1, which risks mutating into a form that's easily spread among people. Such a virus could touch off a pandemic similar to the one that killed as many as 50 million people in 1918.
Human cases have been reported from nine of Turkey's 81 provinces, prompting calls yesterday from the European Union for countries near Turkey to step up surveillance and control activities to prevent further spread.
At least 147 human cases of H5N1 have been confirmed in Vietnam, Thailand, Indonesia, China, Cambodia and Turkey, the United Nations health agency said on Jan. 10. Of those, 78 have died. Reports of new human H5N1 cases have increased each month since August, reaching 11 in December.
Contact with infected birds is the principal source of infection and there's no evidence of sustained human-to-human transmission occurring in countries experiencing human cases, the WHO said.
``We need more information to make any conclusions'' about the cases in Turkey, said Hitoshi Oshitani, a professor at Japan's Tohoku University and the former leader of the WHO's avian influenza outbreak team in the Western Pacific. ``This virus is continually changing. We need further testing.''
Turkey has reported 18 laboratory-confirmed avian flu cases, of which three, all from the same family, were fatal. Yesterday, the virus was detected in samples from children, aged four and six years, from Sanliurfa Province, near the southern border with Syria, and Siirt Province, which is adjacent to Van in the eastern part of the country, the UN agency said in the statement.
In Sanliurfa province, outbreaks in backyard poultry are now thought to date to late November 2005. That would be at least a month earlier than reported. Officials have confirmed poultry outbreaks in 11 Turkish provinces and are investigating possible outbreaks in an additional 14 provinces across the country, the WHO said.
The pathogen sickening people in Turkey appears similar to the H5N1 found in birds in the country and is closely related to viruses isolated from a large outbreak in migratory birds that occurred at the Qinghai Lake nature reserve in China, it said. That outbreak began in late April 2005.
The WHO's U.K. collaborating laboratory plans to test more specimens. Interpretation of the significance of the initial finding for human health will depend on clinical and epidemiological data being gathered by international experts in Turkey who are probing the possibility of any human-to-human transmission, the vulnerability to infection of healthcare workers, and the possibility that milder forms of the disease might be occurring, the WHO said.
Two brothers, aged four and five years, were hospitalized in Ankara after testing positive to H5N1 following contact with sick birds. Neither has influenza symptoms, the International Herald Tribune reported on Jan. 11, citing Guenael Rodier, who is leading a WHO bird flu study in Turkey.
Evidence of milder forms of H5N1 and cases where infection hasn't caused clinical symptoms would add fuel to an ongoing debate over the true number and severity of human infections.
``If there are many mild or a asymptomatic cases, we may have missed many cases,'' Oshitani said in an interview in Tokyo today.