Experts study behavior of H5N1 virus in Vietnam, China

Jun 24, 2005 (CIDRAP News) – As poultry were being culled in China and Vietnam to prevent further spread of avian influenza outbreaks this week, international experts were visiting both countries to better understand how the H5N1 virus is behaving.

Ducks in central Vietnam were being culled after authorities discovered that one-fifth of the waterfowl in Quang Tri province carry the H5N1 virus, China's Xinhau news service reported today, basing the story on a Vietnamese newspaper, Saigon Liberation. More than 23,000 birds have already been culled in 38 infected flocks, with another 144 flocks untested, Xinhua reported.

As many as 120,000 to 150,000 birds may be culled, according to a report today by the Vietnamese news service Thanh Nien News, which also cited the Saigon Liberation as its source.

In response to the outbreaks, the Agriculture and Rural Development Ministry extended an existing ban on egg incubation for breeding poultry and building new waterfowl or quail flocks through February 2006, according to the Vietnam News Service (VNS). In addition, the country's state bank has asked that commercial banks refuse loans to farmers and businesses that produce breeding poultry and waterfowl, VNS reported today.

This is the second outbreak in Vietnamese poultry in about a week. Prior to that, the country had been free of bird outbreaks since April, Xinhua reported. However, human cases of H5N1 infection have continued without a major break since mid-December 2004.

Possible and confirmed human H5N1 infections in Vietnam are the focus of intense study by a visiting team of experts from Britain, Hong Kong, Japan, and the United States, according to a Canadian Press (CP) report today. The team of about half a dozen virologists and epidemiologists is investigating whether the H5N1 virus has changed in ways that make a flu pandemic more likely.

The team is working in Vietnam at the government's request, Maria Cheng, a World Health Organization (WHO) spokeswoman, told the CP.

Their tasks include studying clusters of cases to determine the extent of human-to-human transmission and analyzing tests on hundreds of stored human blood samples that may indicate scores of undetected human H5N1 infections, the CP reported.

Those findings are questionable because they relied on the Western blot test, which is not the gold standard for flu testing, the CP story said.

Authorities are negotiating to transfer the blood samples to a site where appropriate tests can be performed—a lab with the biosafety rating to conduct neutralization assays considered the gold standard for flu testing, the CP reported.

In China, international experts sent by the WHO and the Food and Agriculture Organization (FAO) were studying the H5N1 outbreak in Qinghai province this week and recently received approval to do the same in neighboring Xinjiang province, the International Herald Tribune reported yesterday.

China has had three avian outbreaks of H5N1 in recent weeks, including one this week that involved the deaths of 180 ducks and geese, according to its reports to the World Organization for Animal Health (OIE). In all, at least 1,490 birds were culled, according to a Jun 21 story by Agence France-Presse (AFP).

Authorities are also pressuring China for details of farmers' reported use of the human antiviral drug amantadine to control and prevent poultry outbreaks of H5N1. Scrutiny has extended to questions over whether China has used oseltamivir, one of a newer class of human antiviral drugs, on poultry, the CP reported on Jun 23.

The WHO asked China to investigate whether farmers have used oseltamivir in poultry, and the FAO has urged China to prevent such use, the CP story said. Several countries are stockpiling oseltamivir for use in the event of a flu pandemic. Current strains of H5N1 are resistant to amantadine, but it could also be useful in a pandemic, depending on the nature of the pandemic virus, experts say.

A spokesman for the company that makes oseltamivir, Roche, said the company doesn't sell the product to agro-chemical businesses, the CP story said.

The report quoted WHO spokesman Dick Thompson as saying, "It's clear to us that the [Chinese] Ministry of Health shares our concerns about this and they understand the importance of . . . the possible use of this antiviral in agriculture, that it might force or speed [development of] a resistant strain."

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