Newscast Media WASHINGTON—An emerging influenza virus, making its first appearance in humans in 2013, is not the serious human health threat that some experts have feared since the unusual pathogen sickened almost 140 in China.
The H7N9 virus killed more than 40 people in urban China earlier this year, but a U.S.-backed research team now finds that the virus is not well-adapted for transmission from human to human. The Scripps Research Institute published the findings in the journal Science.
“Luckily, H7N9 viruses just don’t yet seem well-adapted for binding to human receptors” at the cellular level, said Ian Wilson, a leading biologist at Scripps. The National Institute of Allergy and Infectious Diseases provided financial support for the study.
When birds are infected with H7N9, it causes them few or no symptoms. But humans became severely ill in China starting in February, and, ultimately, 139 laboratory-confirmed cases of the virus were documented, with an alarming fatality rate of almost 30 percent.
Tests on tissue samples from the infected humans began quickly at a number of laboratories, with researchers attempting to identify whether H7N9 had become capable of jumping the species barrier that protects people from many flu strains that occur in animals. If H7N9 had adapted to obtain a lock onto human cells, the potential for a human influenza pandemic loomed.
Viral mutations allowing a leap across the species barrier have been identified as enablers of the 1968–69 Hong Kong flu, which killed 1 million. The worst worldwide flu epidemic ever documented, in 1918–19, caused an estimated 50 million fatalities and broad social disruption. It too arose after a flu virus jumped the species barrier.
While the first studies of H7N9 indicated the virus had some capability to lock onto human receptor cells, the Scripps study conducted a more thorough analysis to find that only a weak attachment forms between the viral proteins and human cells.
“These results suggest that we should continue to observe H7N9 and see if it undergoes any changes that make it more likely to spread in the human population,” Wilson said.
Health authorities worldwide are on the lookout for H7N9 and are reporting cases to the World Health Organization (WHO), the authoritative source for case statistics. WHO reports that most human sickness has arisen after people had direct contact with poultry or live animal markets.
The most recent WHO assessment indicates that the H7N9 virus could remain in circulation in China and neighboring nations. With the Northern Hemisphere flu season underway, further cases “would not be unexpected,” WHO reports.