There's evidence the new H7N9 bird flu virus is transmitted from chickens at poultry markets in China to humans, a small study suggests.

In Thursday's online issue of the medical journal The Lancet, researchers gave some of the first detailed information about how H7N9 affects people.

Scientists compared throat and lower respiratory swabs from four people who caught the virus to swabs from 86 birds at live markets in eastern China. They also examined the genetic sequence of the virus.

"Cross species poultry-to-person transmission of this new … H7N9 virus is associated with severe pneumonia and multiorgan dysfunction in human beings," Dr. Yu Chen of Zhejiang University in Hangzhou, China, and co-authors concluded.

The scientists found the virus from one patient was nearly identical to one found in a chicken.

The findings offered doctors and scientists clues to understanding the emerging virus, Marion Koopmans of Netherlands' Centre for Infectious Disease Control and Menno de John of the University of Amsterdam said in a journal commentary published with the study.

For example, the virus might not be detected in patients' throat swabs but could be found in lower respiratory tract specimens.

Unlike the H5N1 avian flu where most cases were in previously healthy children or young adults, the patients infected with H7N9 had a median age of 63.

Scientists from the World Health Organization who visited areas of outbreak of the new bird flu were told that older men in the household generally did the shopping for live birds, said Dr. Keiji Fukuda, the agency's assistant director for health security and the environment.

Earlier this week, Chinese doctors reported in the New England Journal of Medicine health that 54 of 71 (76 per cent) patients with available data so far had underlying medical conditions. 

Similarly, 77 per cent of patients said they had recent exposure to animals while working at or visiting a live-animal market, including 45 who had exposure to chickens, 12 to ducks, and four to swine with the rest mentioning pigeons, geese, quail, wild birds, pet birds, cats and dogs.

The human and animal viral sequences are closely related but were diverse enough to conclude H7N9 has been circulating for a while, most likely among animals, the Lancet commentators said.

"I think it's fair to say that this avian influenza virus appears to be more infectious to people than any other avian influenza virus we know," Fukuda said of H7N9. It has genetic mutations that suggest it is better adapted to infecting mammals compared with other bird flu viruses.

Researchers are also looking for signs of sustained transmission to estimate the pandemic potential of the virus.

Experts had suspected birds in live markets to be the source of infection but it wasn't clear if other animals or wild birds might also be responsible.

"Aggressive intervention to block further animal-to-person transmission in live poultry markets, as has previously been done in Hong Kong, should be considered," Kwok-Yung Yuen of the University of Hong Kong, who led the study, told The Lancet.

It's hoped that wide culls of poultry carrying the disease will curb its spread, although H7N9 doesn't appear to sicken chickens.

To learn more, the Public Health Agency of Canada said it is has received a live sample of the H7N9 virus from the U.S. The agency is also preparing to receive samples directly from China.

Scientists at the agency's National Microbiology Laboratory in Winnipeg are conducting studies on this virus to:

  • Determine if antiviral drugs are effective against the virus.
  • Develop and test vaccines to determine if they protect against the virus.
  • Develop important diagnostic tests, such as to detect antibodies against the virus and monitor for any changes in it.

So far, H7N9 has infected more than 100 people in China and killed more than 20.

With files from The Associated Press and The Canadian Press