H5N1 virus change may ease jump from birds to humans, WHO says

Jan 12, 2006 (CIDRAP News) – An H5N1 avian influenza virus recovered from a Turkish patient has a mutation that may enable the virus to spread more easily from birds to humans, though the finding's significance for human health is not yet clear, the World Health Organization (WHO) reported today.

Viruses recovered from the first two Turkish children to die of avian flu have been analyzed in London, the WHO said. A sample from one of the patients has a mutation at "the receptor-binding site," a reference to hemagglutinin, a protein that enables flu viruses to attach to and enter host cells.

"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," the WHO said. "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 [London] laboratory anticipate that the Turkish virus will also have this characteristic."

What the finding may mean for human health will depend on clinical and epidemiological data now being gathered in Turkey, the agency said. It added that it has found no evidence of sustained person-to-person transmission of the virus in any country so far.

In a Washington Post report today, the WHO's Michael Perdue called the finding "a little concerning because the virus is still trying new things in its evolution." Perdue is overseeing the WHO's response to the Turkish outbreak from agency headquarters in Geneva, the story said.

The WHO statement did not suggest whether the mutation could be a factor in the rapid increase in reported human cases in Turkey since the first two were revealed Jan 4. The number reached 18 today with the report that three more Turkish children have tested positive for an H5 avian flu virus, a finding that usually points to H5N1. The tests were done in a Turkish lab.

The cases include two children, aged 4 and 6, in Sanliurfa province in southern Turkey and in Siirt province in the east, the WHO reported. Both had contact with sick birds. The other patient was a 12-year-old girl who died Jan 7 in eastern Turkey and was the sister of two teenagers who died of avian flu earlier.

The WHO so far has officially recognized just four cases in Turkey on the basis of confirmation by outside labs.

The analysis by the British lab showed that the viruses from the two Turkish children were very similar to H5N1 viruses recovered from birds in Turkey, the WHO said. The viruses were also closely related to viruses isolated from migratory birds that died at the Qinghai Lake nature reserve in China last spring.

The WHO said the studies also indicate that the Turkish viruses are sensitive to both classes of antiviral drugs used against flu: oseltamivir (a neuraminidase inhibitor) and amantadine (an adamantane). H5N1 viruses are usually described as insensitive to adamantanes, though some strains have been susceptible.

"WHO and collaborating experts will review the data on amantadine sensitivity. Oseltamivir remains the drug of first choice recommended by WHO," the agency said.

The agency said its pandemic alert level is still in phase 3: "human infections with a new virus subtype are occurring, but the vast majority of these infections are acquired directly from animals."

See also:

Jan 12 WHO news release
http://www.who.int/csr/don/2006_01_12/en/index.html

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