H7N9 bird flu found to spread through the air

Virus can also infect pigs, say HKU researchers, who warn officials to maintain tight scrutiny even though threat seems under control

Friday, 24 May, 2013, 5:50am

Jeanette Wang jeanette.wang@scmp.com


Chickens are sold at a a live poultry stall in Kowloon City wet market. Photo: Edward Wong

The H7N9 bird flu virus can be transmitted not only through close contact but by airborne exposure, a team at the University of Hong Kong found after extensive laboratory experiments.

Though the virus appears to have been brought under control recently, the researchers urged the Hong Kong authorities to maintain strict surveillance, which should include not only poultry but humans and pigs.

“We also found that the virus can infect pigs, which was not previously known,” said Dr Maria Zhu Huachen, a research assistant professor at HKU’s School of Public Health.

There have been 131 confirmed human infections, with 36 deaths, the World Health Organisation said. All but one of the cases was on the mainland. The virus appears to have been brought under control largely due to restrictions at bird markets and there have been no new confirmed cases since May 8.

But Zhu said that although there was no evidence of sustained human-to-human transmission, their study provided evidence that H7N9 was infectious and transmissible in mammals.

In the study, to be published today in the journal Science, ferrets were used to evaluate the infectivity of H7N9. It was found the virus could spread through the air, from one cage to another, albeit less efficiently.

Inoculated ferrets were infected before the appearance of most clinical symptoms. This means there may be more cases than have been detected or reported.

We also found that the virus can infect pigs, which was not previously known … People may be transmitting the virus before they even know that they’ve got it
Dr Maria Zhu Huachen, HKU’s School of Public Health

“People may be transmitting the virus before they even know that they’ve got it,” Zhu said.

Additional tests using pigs, a major host of influenza viruses, showed that they could also get infected with H7N9. Zhu warned that H7N9 may combine with pig viruses to generate new variants.

On a more positive note, it was found that the virus is relatively mild.

“Most of the fatal H7N9 cases had underlying medical conditions, so there are probably some other factors that contribute to this kind of fatality,” Zhu said.

 

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Scientists create hybrid flu that can go airborne

H5N1 virus with genes from H1N1 can spread through the air between mammals.

02 May 2013

Researchers have crossed two strains of avian flu virus to create one that can be transmitted through the air — and possibly settle on the cilia of lung cells as in this conceptual image.

KARSTEN SCHNEIDER/SCIENCE PHOTO LIBRARY

As the world is transfixed by a new H7N9 bird flu virus spreading through China, a study reminds us that a different avian influenza — H5N1 — still poses a pandemic threat.

A team of scientists in China has created hybrid viruses by mixing genes from H5N1 and the H1N1 strain behind the 2009 swine flu pandemic, and showed that some of the hybrids can spread through the air between guinea pigs. The results are published in Science1.

Flu hybrids can arise naturally when two viral strains infect the same cell and exchange genes. This process, known as reassortment, produced the strains responsible for at least three past flu pandemics, including the one in 2009.

There is no evidence that H5N1 and H1N1 have reassorted naturally yet, but they have many opportunities to do so. The viruses overlap both in their geographical range and in the species they infect, and although H5N1 tends mostly to swap genes in its own lineage, the pandemic H1N1 strain seems to be particularly prone to reassortment.

“If these mammalian-transmissible H5N1 viruses are generated in nature, a pandemic will be highly likely,” says Hualan Chen, a virologist at the Harbin Veterinary Research Institute of the Chinese Academy of Sciences, who led the study.

“It’s remarkable work and clearly shows how the continued circulation of H5N1 strains in Asia and Egypt continues to pose a very real threat for human and animal health,” says Jeremy Farrar, director of the Oxford University Clinical Research Unit in Ho Chi Minh City, Vietnam.

Flu fears

Chen’s results are likely to reignite the controversy that plagued the flu community last year, when two groups found that H5N1 could go airborne if it carried certain mutations in a gene that produced a protein called haemagglutinin (HA)2, 3. Following heated debate over biosecurity issues raised by the work, the flu community instigated a voluntary year-long moratorium on research that would produce further transmissible strains. Chen’s experiments were all finished before the hiatus came into effect, but more work of this nature can be expected now that the moratorium has been lifted.

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