The genetic structure of H5N1 virus recovered from Pakistan's first confirmed human case of the illness suggests the virus did not mutate to become better adapted to humans, an expert with the World Health Organization said Thursday.
Dr. Frederick Hayden said initial sequencing of several genes of the virus showed no worrisome genetic changes. The London-based influenza laboratory that did the work reported that the virus was identical to a number of H5N1 viruses isolated from chickens in the region, he said.
The virus fragments were recovered from specimens taken from a man who died of H5N1 infection on Nov. 28. The WHO believes the man became infected while caring for his brother, a veterinary worker who fell ill after culling H5N1-infected poultry.
"There were no adaptive mutations in the hemagglutinin that would suggest that it have moved towards human binding characteristics, which is of course good news,'' said Hayden, a medical officer with the WHO's global influenza program.
"If you look at the sequence findings combined with the epidemiologic investigations that have been done to date, it really does suggest that the H5 virus has not gained a capacity for spread from human-to-human within either Pakistan or more broadly.''
Several other members of the family initially tested positive in diagnostic work conducted by Pakistan's National Institute of Health. But confirmatory tests done by international labs working with the WHO only produced the one positive result.
The WHO cautioned last week that doesn't mean others in the family weren't infected, noting the samples could have deteriorated by the time they reached the London lab.
It is hoped follow-up blood testing will reveal whether -- as the WHO suspects -- a number of other members of the family were also infected, including the veterinary worker. Another brother who nursed the veterinary worker also fell was ill but he died without being tested.
Hayden said the initial sequencing shows the virus is from a family or clade of H5N1 viruses identified as "Qinghai Lake'' like viruses. That family of viruses spread from a lake in northwestern China in 2004 into Russia, Europe and eventually the Middle East and Africa.
Like most viruses in that grouping, known as clade 2.2, the virus from the Pakistan man appears to be susceptible to both classes of influenza drugs -- neuraminadase inhibitors (Tamiflu and Relenza) and M2 inhibitors (amantadine and rimantadine).
Hayden said sequencing of the full genome of virus grown from a specimen taken from the Pakistani man remains to be completed.
In other H5N1 developments, Israeli media reports Thursday suggested authorities in that country had ordered the culling of poultry in part of Israel's north after chickens kept at a kindergarten tested positive for the strain of avian flu.
Most of the chickens in the coop in a Binyamina kindergarten died, and veterinarians determined they were infected with the H5N1 strain of avian flu, it was reported.
Israel TV showed footage of yellow-suited, masked workers disinfecting the kindergarten in the northern Israeli town.
Fowl were to be culled in a three-kilometre radius from Binyamina, near Israel's Mediterranean coast south of the port city of Haifa, the reports said.
