The bird flu strain H7N9, which had so far infected 131 and killed 36 in China, could be passed on between humans through the air and close contact.

Using ferrets that were injected with the new H7N9 strain, scientists at Shantou University, the University of Hong Kong as well as colleagues in the US and Canada observed and found that the virus could spread through the air, from one cage to another.

The H7N9 virus is seen to mutate over time, thus becoming more transmissible in humans as time goes by, Richard Webby, a virologist at St. Jude Children's Hospital in Memphis, Tenn. and a co-author of the paper, said.

Flu transmission in ferrets forecast likely patterns in humans, the authors said in the study published Thursday in the online edition of the journal Science.

"The emerging human H7N9 influenza is infectious and transmissible in mammals," the study said.

"Under appropriate conditions, human-to-human transmission of the H7N9 virus may be possible," it added.

Read: China Virus Alert: H7N9, H5N1 Strains Active, Tibet Outbreak Kills 1 Child

Dr Maria Zhu Huachen, a research assistant professor at HKU's School of Public Health, said they also observed that the virus can infect pigs, which was not previously known.

But the good news was that the pigs did not pass the virus to each other.

"If the study has shown that one pig had easily infected another pig, then I would be more concerned," Anthony Fauci, head of the US National Institute of Allergy and Infectious Diseases.

Read: As China Bird Flu Death Toll Now at 31, Infections Among Pigs Also Rising

"Under very experimental circumstances, one mammal can infect another one by direct contact," he told AFP.

"Saying that we are now in a greater danger of a pandemic is probably an exaggeration," he added. "It's obviously something we need to keep an eye on to make sure we understand the virus better."

Based from the organs of infected ferrets, researchers detected the H7N9 virus can infect the upper and lower respiratory tracts, and lymph nodes and potentially the brain.

Read: Bird Flu Strain H7N9 Hitting China Not Yet a Pandemic, But..

"It seemed significant to me that that much virus is reaching the brain," Suresh Mittal, a bird flu expert and professor of comparative pathology at Purdue University, told AFP.

Mr Mittal said highly pathogenic viruses are not often seen in human flu pandemics, thus he urged more research into the subject.

"Physicians will be more careful looking at patients and seeing if patients develop signs of encephalitis or not," he said.

According to the latest update on human infections released by the World Health Organization, no new lab-confirmed cases of H7N9 in humans were reported between May 8 and May 17.

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