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Sunday 24th June 2018

Bird flu gene identified

6th November 2006

15032006_H5N1.jpgChinese scientists have identified a gene in the H5N1 bird flu virus that they say is responsible for its virulence in poultry, paving the way for new vaccines.

There are many different strains of H5N1, some of which kill more than half the people they infect, while others do little or no harm.

Bu Zhigao at the Harbin Veterinary Research Institute said researchers could now understand how the virus becomes lethal, and the molecular basis for its pathogenicity.

The researchers zeroed in on the virulent gene after analyzing two closely related strains of the H5N1 obtained from infected geese in Guangdong in 1996 - one highly pathogenic in chickens and the other harmless. Differences between the two strains were located in four genes, they found.

The scientists designed four genetically modified viruses each containing one of the four genes in question and tested them on laboratory chickens.

Only chickens infected with the modified virus containing the highly pathogenic gene died. The other chickens had no signs of disease, the scientists wrote in this month's issue of the Journal of Virology.

"Now that we know the special role of the [highly pathogenic] NS1 gene, we can think about developing a vaccine," Bu said, adding that a vaccine that neutralizes the gene known as NS1 could be quickly designed.

The scientists come from the Ministry of Agriculture's Animal Influenza Laboratory, the National Key Laboratory of Veterinary Biotechnology, Chinese Academy of Agricultural Sciences and the Harbin Veterinary Research Institute.

H5N1 remains largely a disease in birds although it has killed over 150 people, mostly in Asia, since 2003. Experts fear it could spark a pandemic and kill millions of people if it begins to transmit efficiently among humans.

Meanwhile, Chinese scientists have rejected the results of a study that reported a prevalent new strain of bird flu in the country, saying they have not found significant variants to the virus.

The Hong Kong and U.S. scientists who carried out the study said the new strain - called H5N1 Fujian-like - was found in almost all poultry outbreaks and some human cases in southern China and was now also the primary version in Hong Kong, Laos, Malaysia and Thailand.

The Hong Kong and U.S. researchers "lack scientific proof," said Chen Hualan, director of the National Bird Flu Reference Laboratory.

"The so-called `Fujian-like virus' is not a new variant of the virus," the China Daily newspaper quoted Chen, whose lab does isolation and gene sequence analysis on samples from every domestic bird flu outbreak, as saying.

Guan Yi, one of the study's authors, said he had not seen data from Chen's lab and could not comment on her claims.

But "the data from our systematic influenza surveillance was subject to scientific peer review and published in an international journal of high repute," Guan, who heads the emerging infectious diseases lab at Hong Kong University, said. "I therefore stand by those findings."

New strains of viruses emerge regularly, but health experts need to know when any one becomes dominant so they can work to develop a vaccine.

Concerns are particularly strong that the virus could mutate into a strain easily passed between humans and spark a pandemic.

Most human infections have been traced to contact with sick birds.

International health experts have repeatedly complained about Chinese foot-dragging in cooperating on investigating emerging diseases such as bird flu and SARS, which emerged in southern mainland provinces in late 2002 and eventually killed 774 people worldwide.

The study, released in the Proceedings of the National Academy of Sciences, charted the spread of the new strain by testing geese and ducks found in live markets in six southern mainland provinces beginning in June last year.

Over the course of the year, the new strain became more pervasive, the study said. Among the 108 samples taken from poultry this April and June, 103 - or 95 percent - were infected with the Fujian-like strain, the scientists said.

The researchers said it was unclear how the strain had emerged or spread so widely.

Chen said that, between last year and this year, the lab had isolated viruses in waterfowl in the mainland's southern regions that were reported to the United Nation's Food and Agriculture Organization and the Paris-based World Organization for Animal Health.

"These viruses all remain steady in gene type and there is no marked change in their biological characteristics," she was quoted as saying.

Guan said he "would welcome this information being made available so that the world could have a comprehensive picture of the origin and evolution of H5N1 variants."

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