Scientists are gaining a better understanding of the H7N9
Working with ferrets, an animal that is often studied to gain insight into
But H7N9 only spread efficiently when the ferrets were placed in the same cage and came into direct contact. The virus did not transmit easily between animals in adjacent cages, who couldn't touch but could breathe in the droplets from each others' sneezes and coughs.
"We think for a virus to take off in humans, it has to be efficient at both" forms of transmission, said Richard Webby, a virologist at St. Jude Children's Hospital in Memphis, Tenn. and a coauthor of the paper. But, he added, the H7N9 virus is likely to mutate over time, and could become more transmissible in humans as time goes by.
Webby said that the team's data reflected the epidemiology on the ground: So far, public health officials believe most cases have occurred in people who have had close contact with poultry, and do not think H7N9 spreads easily between humans. But even though the findings "may seem a little 'duh,' " Webby said, they help scientists answer some of the more subtle questions surrounding H7N9 transmissibility in people.
When people get sick with H7N9, health workers don't know how much of their susceptibility is influenced by underlying heath conditions, cross-reactive immunity, or other external factors. By performing an experiment in ferrets, Webby said, researchers can control for such variables and get a more clear picture of the virus' transmissibility.
The team also performed their experiment in pigs, in an effort to see what role the animals might play in harboring the virus in the wild. H7N9 did not transmit efficiently in the pigs, suggesting that they "probably are not big players in the epidemiology of the disease at the moment," Webby said.
According to the World Health Organization's latest update on human infections with H7N9, there were no new lab-confirmed cases of H7N9 in humans between May 8 and May 17. Webby said that cases of the illness did seem to be "tailing off," perhaps because live poultry markets have been shut down in the region, or perhaps because it's almost summer.
In the future, the coauthors of the Science paper wrote, as markets reopen, authorities in areas where the virus has taken hold may want to adjust the way they manage poultry markets to prevent further spread of the virus.