Preliminary studies suggest no major genetic changes in the H5N1 avian influenza virus in Egypt that would help explain the country's busiest month ever for human cases, the World Health Organization (WHO) said in a report released today.
The agency said the spurt of cases is probably explained by increased circulation of the virus in poultry and various other factors, including seasonal ones, and that the risk of community-level spread of the virus remains low.
In its update on "Influenza at the Human-Animal Interface," the WHO said 18 lab-confirmed H5N1 cases were reported in Egypt from Dec 4 to Jan 6, the most in any single month. Two of the cases had onset in November, with the rest in December. Media reports have cited several more H5N1 cases in Egypt in the past week, including six since Jan 9.
The flurry of cases has triggered some speculation about whether the virus is evolving to become better adapted to humans. Last week the United Nations Food and Agriculture Organization (FAO) said scientists who recently analyzed poultry H5N1 isolates in Egypt found two mutations that are typically associated with adaptation to mammals. But the FAO also said an analysis of two recent human isolates from Egypt showed no major genetic changes.
The WHO report says, "Although all influenza viruses evolve over time, preliminary laboratory investigation has not detected any major genetic changes in the viruses isolated from the patients or animals compared to previously circulating isolates."
Possible causes of surge
The agency said probable reasons for the surge of cases include increased H5N1 circulation in poultry, lower public awareness of risks in Middle and Upper Egypt, and seasonal factors "such as closer proximity [of people] to poultry and longer survival of the viruses in the environment because of cold."
Despite the jump in cases, human infections remain rare, and the viruses do not appear to spread easily among people, the WHO added. "As such, the risk of community-level spread of these viruses remains low."
The report says the December cases in Egypt included one small cluster in Giza governorate, involving confirmed cases in two small children and a probably case in their mother, who died without being tested for H5N1. All the patients were exposed to sick or dead poultry.
The agency said that sporadic cases and small clusters are not unexpected, given the virus's circulation in poultry.
H5N6 case in China, various strains in birds
In other observations, the report notes the second human case of H5N6 avian flu, reported last month in a man from China's Guangdong province who had been exposed to poultry. The case seems to be an isolated one, but because the virus seems to be circulating widely in poultry, further cases would not be surprising, the WHO said.
Amid a number of avian flu outbreaks involving various subtypes on several continents, the agency said the number of outbreaks is at the expected level for this time of year, "although novel strains of various subtypes have been detected for the first time in birds in new geographic regions."
Mentioning H5N8, H5N2, and H5N3 outbreaks in Europe, North America, and Asia, the WHO said, "Although influenza A(H5N8) might have the potential to cause disease in humans, so far no human cases of infection have been reported."
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