Since it was first identified by Chinese authorities two months ago, the new H7N9 bird flu has infected 131 people in eastern China. The virus produces severe pneumonia, with most patients requiring hospitalization, and statistics [pdf] released last week by the WHO indicate that 32 of those infected have died of the virus.
Now a study in ferrets, considered the best model animal of flu transmission in humans, has found that the virus is transmissible via air and direct contact, making it possibly capable of human-to-human transmission as well. Such transmission was seen with the last major bird flu threat, H5N1, but it was limited to small number of cases.
Some of the people with confirmed H7N9 had had contact with animals, and the virus has been found in birds at markets in the area. Since the virus has occurred in family clusters, public health officials are concerned that it might also be transmissible between people, a prerequisite for a disease to cause a pandemic. However transmissibility from human to human has not been observed.
In the current study, researchers infected six ferrets with H7N9 virus isolated from one of the fatal cases. Samples revealed that the virus had successfully taken hold in these animals even before the appearance of most clinical signs (in ferrets, sneezing, runny nose, cough and fever)—raising the possibility that humans, too, could be infectious before they are symptomatic. That could aid the virus’s spread.
When uninfected ferrets were housed in the same cage as infected ferrets, they all ended up with the virus, suggesting that H7N9 can spread through direct contact.
The virus was also found to spread through the air, though not as efficiently. Only one of three ferrets caged nearby the infected ferrets caught the virus.
Because H7N9 doesn’t transmit very well through the air, its pandemic potential is curtailed thus far. But future mutations to the virus may increase its transmissibility by air. And since the virus was transmissible in ferrets that raises the possibility that human-to-human transmission may be presently happening in eastern China.
The authors advise that more oversight—probably meaning more testing—of live poultry markets is needed to keep the virus from becoming endemic in birds, which would increase the likelihood of it mutating and becoming capable of causing a pandemic.
Photo by ironypoisoning via Flickr