WHO warns that avian flu could still be in the environment
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《英国医生杂志》
The World Health Organization has cautioned countries where poultry flocks have been decimated by H5N1 avian influenza not to declare prematurely that the outbreak is over. An estimated 80 million birds have been culled, but the virus in poultry continues to spread in several areas, particularly in China.
A leopard in a zoo in Central Thailand has died of H5N1 avian flu earlier this week, the first known case of infection in the cat family. Outbreaks of the virus have also been reported in eight Thai provinces, where it was thought to have been eliminated, and there have been outbreaks reported in parts of China which were previously unaffected, including Tibet.
Even in places where birds have been removed, there is a continuing risk to human health, said Peter Cordingley, WHO抯 spokesman in Manila, in the Philippines.
"What we are worried about is if governments go ahead and declare the outbreak over once the culling is finished," he said. "The risk is not over because the virus could still be present in the environment. If farmers restock too soon and there is another outbreak, it will be much more difficult to persuade them to cull again and then you have an endemic situation where the virus is able to jump all the time. All talk of the outbreak being over in a few weeks?time is dangerous talk."
Preliminary analysis of the data from Vietnam indicates that the virus has high mortality, with death occurring a mean of 10 days after the onset of illness. "However, these cases were identified by alert clinicians in tertiary care hospitals and cannot be taken to be representative of the full range of illness that H5N1 may cause," the report said. Since 16 February the H5N1 avian flu virus has caused 20 deaths—14 in Vietnam and six in Thailand—and WHO expects more cases to emerge in all countries where there are currently widespread poultry infections. "We think there will be more human cases coming down the pipeline," said Mr Cordingley.
Initial theories about the origin of the current outbreak are beginning to emerge. According to a report in New Scientist, similarities between the genetic sequence of the H5N1 flu virus from one of the recent fatal cases in Vietnam is highly similar to the sequences recently taken from ducks and geese in China, which indicates that the virus has been circulating in Asia for some time. Research on the virus shows that it has been rapidly mutating in response to "unusual selective pressure," the report said.
The widespread vaccination of poultry could exert such pressure, the report said, and the start of widespread vaccination of poultry in China coincides with the period in which the number of variations in the virus has risen sharply. However, lack of samples from other countries in Asia, which until recently denied having cases of H5N1 flu in poultry, meant that the sources of the virus cannot yet be definitively pinpointed, the report said.
Preliminary clinical data on 10 cases, an epidemiological review of the outbreak in Vietnam, a case definition for global reporting, and chronology of key events are at www.who.int/csr/disease/avian_influenza. WHO has also published data on five cases in Thailand (www.who.int/wer/2004/en/wer7907.pdf).(Hong Kong Jane Parry)
A leopard in a zoo in Central Thailand has died of H5N1 avian flu earlier this week, the first known case of infection in the cat family. Outbreaks of the virus have also been reported in eight Thai provinces, where it was thought to have been eliminated, and there have been outbreaks reported in parts of China which were previously unaffected, including Tibet.
Even in places where birds have been removed, there is a continuing risk to human health, said Peter Cordingley, WHO抯 spokesman in Manila, in the Philippines.
"What we are worried about is if governments go ahead and declare the outbreak over once the culling is finished," he said. "The risk is not over because the virus could still be present in the environment. If farmers restock too soon and there is another outbreak, it will be much more difficult to persuade them to cull again and then you have an endemic situation where the virus is able to jump all the time. All talk of the outbreak being over in a few weeks?time is dangerous talk."
Preliminary analysis of the data from Vietnam indicates that the virus has high mortality, with death occurring a mean of 10 days after the onset of illness. "However, these cases were identified by alert clinicians in tertiary care hospitals and cannot be taken to be representative of the full range of illness that H5N1 may cause," the report said. Since 16 February the H5N1 avian flu virus has caused 20 deaths—14 in Vietnam and six in Thailand—and WHO expects more cases to emerge in all countries where there are currently widespread poultry infections. "We think there will be more human cases coming down the pipeline," said Mr Cordingley.
Initial theories about the origin of the current outbreak are beginning to emerge. According to a report in New Scientist, similarities between the genetic sequence of the H5N1 flu virus from one of the recent fatal cases in Vietnam is highly similar to the sequences recently taken from ducks and geese in China, which indicates that the virus has been circulating in Asia for some time. Research on the virus shows that it has been rapidly mutating in response to "unusual selective pressure," the report said.
The widespread vaccination of poultry could exert such pressure, the report said, and the start of widespread vaccination of poultry in China coincides with the period in which the number of variations in the virus has risen sharply. However, lack of samples from other countries in Asia, which until recently denied having cases of H5N1 flu in poultry, meant that the sources of the virus cannot yet be definitively pinpointed, the report said.
Preliminary clinical data on 10 cases, an epidemiological review of the outbreak in Vietnam, a case definition for global reporting, and chronology of key events are at www.who.int/csr/disease/avian_influenza. WHO has also published data on five cases in Thailand (www.who.int/wer/2004/en/wer7907.pdf).(Hong Kong Jane Parry)