Some strains of bird flu are coming ever closer to developing the traits they need to cause a human pandemic, a study released yesterday said. Researchers who analyzed samples of recent avian flu viruses found that a few H7 strains of the virus that have caused minor, untransmissible infections in people in North America between 2002 and 2004 have increased their affinity for the sugars found on human tracheal cells.
Subsequent tests in ferrets suggested that these viral strains were not readily transmissible. But one strain of the H7N2 virus, a low pathogenic avian flu strain isolated from a man in New York in 2003, replicated in the ferret’s respiratory tract and was passed between infected and uninfected ferrets suggesting it could be transmissible in humans.
The investigators said the evidence suggests that the virus could be evolving toward the same strong sugar-binding properties of the three worldwide viral pandemics in 1918, 1957 and 1968.
“These findings suggest that the H7 class of viruses are partially adapted to recognize the receptors that are preferred by the human influenza virus,” said Terrence Tumpey, a senior microbiologist with the US Centers for Disease Control and Prevention in Atlanta, Georgia.
The authors said that if the viruses continue to evolve in this direction, the avian flu viruses could travel more easily between other animals and humans.
They called for strict surveillance of avian flu viruses and continuing federal preparations for a possible future pandemic.
The study appears in the Proceedings of the National Academy of Sciences.