Robert Roos  News Editor

Feb 9, 2004 (CIDRAP News) – An outbreak of avian influenza at a farm in Delaware has been blamed on an H7 influenza virus, which does not infect humans, unlike the H5N1 subtype causing the widespread avian flu outbreaks in Asia.

Delaware officials announced the outbreak Feb 6. Michael T. Scuse, state secretary of agriculture, attributed the outbreak to an H7 virus and said all poultry housed within 2 miles of the affected farm would be tested. Reuters reported today that 12,000 chickens on the farm had been sacrificed.

The Delaware outbreak caused Japan, Singapore, and South Korea to ban all imports of US poultry, according to Associated Press (AP) reports. Russia, Hong Kong, and Malaysia banned poultry from Delaware only.

Meanwhile, the World Health Organization (WHO) today reported three more confirmed human cases of avian influenza in Vietnam, the hardest-hit country with 18 confirmed cases, including 13 deaths. Also, correcting a Feb 6 report, the WHO said the possibility of person-to-person transmission of avian flu in a family cluster of cases in Vietnam had not yet been ruled out.

In the Delaware outbreak, Scuse called the H7 virus "among the most virulent types" of avian flu viruses, but said it poses "absolutely no risk to human health." Subtypes H5 and H7 of influenza A are the only strains that have caused highly pathogenic avian flu, which spreads rapidly and is often 100% fatal in poultry.

Scuse said the source of the virus was unknown, but the farmer has been involved with the live bird market in New York City. The farmer had been trained to use "biosecure" methods of transporting poultry, Scuse said. However, he said New York state officials told him cases of H7 avian flu have occurred in the live bird market.

Reuters reported today that no disease had been found in tests at five poultry farms within 2 miles of the affected Delaware farm.

The WHO said the latest confirmed human cases of avian flu in Vietnam involved a 6-year-old child who died Feb 3, a 24-year-old man who also died Feb 3, and a 23-year-old man, who remained hospitalized.

The AP reported that a 27-year-old Vietnamese man died of avian flu today at a Ho Chi Minh City hospital. If confirmed to be avian flu, the case would bring the number of human cases to 19.

The WHO said it erred in reporting Feb 6 that genetic sequencing of viruses from two Vietnamese sisters had shown that both viruses were entirely of avian origin and contained no human genes. "WHO has learned that the virus from only one sister has been sequenced, not both sisters," the agency said. "The second virus sequenced was from another case in Vietnam." The virus from the other sister was still being analyzed.

The two sisters were among four family members who had confirmed or suspected cases of avian flu, which suggested possible person-to-person transmission. All the human cases so far have been attributed to exposure to poultry. Disease experts fear that the avian virus could trigger a human flu pandemic if it combines with an ordinary human flu virus and forms a new strain that could spread easily from person to person.

In other developments, the WHO"e;s representative in China, Hank Bekedam, said the extent of the avian flu outbreaks in China suggests that human cases may exist there, though none have been reported so far.

Bekedman said the WHO believes the Chinese government is sharing what it knows about the situation. "However, that may not be the same as knowing all that is happening across the country," he said. "WHO feels it is conceivable that there may be human cases, given the extent of the outbreaks in poultry."

Chinese authorities have reported confirmed or suspected outbreaks of H5N1 avian flu in poultry in 13 provinces and regions, the WHO said. A team of experts from the WHO and the United Nations Food and Agriculture Organization was visiting China"e;s Jiangxi Province, where fresh outbreaks were reported over the weekend, officials said.