Gene Sequencing Information On Human Viruses From First Two Fatal Human Cases In The Turkish Bird Flu Outbreak

The WHO Collaborating Centre for Reference and Research on influenza at the MRC National Institute for Medical Research in Mill Hill, London, has today completed genetic and antigenic analyses of viruses recovered from the first two fatal human cases in the Turkish outbreak.


Information provided to WHO indicates that these viruses are very similar to current avian H5N1 viruses isolated from birds in Turkey. They are also closely related to viruses isolated from the large outbreak in migratory birds that occurred at the Qinghai Lake nature reserve in China, beginning in late April of last year.


These analyses indicate that the Turkish viruses are sensitive to both classes of antiviral drugs, including oseltamivir and amantadine. WHO and collaborating experts will review the data on amantadine sensitivity. Oseltamivir remains the drug of first choice recommended by WHO.


Virus from one of the patients shows mutations at the receptor-binding site. One of the mutations has been seen previously in viruses isolated from a small outbreak in Hong Kong in 2003 (two cases, one of which was fatal) and from the 2005 outbreak in Viet Nam. Research has indicated that the Hong Kong 2003 viruses bind preferentially to human cell receptors more so than to avian cell receptors. Researchers at the Mill Hill laboratory anticipate that the Turkish virus will also have this characteristic.


Interpretation of the significance of this finding for human health will depend on clinical and epidemiological data now being gathered in Turkey.


All available evidence indicates that no sustained human-to-human transmission is occurring in any country experiencing human cases.


The present WHO level of pandemic alert remains at phase 3: human infections with a new virus subtype are occurring, but the vast majority of these infections are acquired directly from animals.


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