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H7N9 Virus May Be Highly Transmissible Among Ferrets, Study Says; Researchers Examine Implications For Human Transmission

“The H7N9 bird flu virus may be highly transmissible among ferrets, a common animal model for studying how flu might spread in humans, Chinese researchers reported Thursday,” Xinhua reports. “Though H7N9 appears to have been brought under control, the researchers warned in a study published online in the U.S. journal Science that the character of the virus, including its pandemic potential, ‘remains largely unknown’ and that it’s possible the virus can efficiently spread between humans eventually,” the news service writes (7/19). “Led by Chen Hualan, one of China’s top virologists, researchers tested the ability of multiple strains of the virus to spread by placing three healthy ferrets in one cage next to three infected ferrets in another cage,” the Wall Street Journal’s “China Real Time Report” notes, adding, “In most cases, only one of the healthy ferrets became infected, but in the case of the Anhui strain, all three of the healthy ferrets became infected with the virus” (Chin, 7/19). “Moreover, testing in ferrets — widely considered to be the best proxy for humans in flu testing — finds that one lethal strain of the virus that killed the first H7N9 victim in China is transmissible via respiratory droplet, meaning that it could conceivably be spread by coughing and sneezing,” Scientific American writes (Maron, 7/18).

“Although the ferret model has its limitations, Chen and co-workers conclude that their findings portend future problems,” according to Science Now, which notes two similar studies — one from the CDC and one by Yoshihiro Kawaoka, a virologist at the University of Wisconsin, Madison, and the University of Tokyo — “reach different conclusions about the severity of the threat” (Cohen, 7/18). “So far, there have been no reports of sustained human-to-human transmission with H7N9 bird flu. But the new findings add to growing evidence that the virus likely needs to undergo just a few genetic mutations to gain the ability to spread between people, said Dr. Richard Webby, a bird flu expert at St. Jude Children’s Research Hospital in Memphis, Tenn., who was not involved in the new study,” LiveScience writes (Rettner, 7/18). In related news, “A 61-year-old woman from northern China was confirmed Saturday as having contracted the deadly H7N9 bird flu virus, state media reported,” Agence France-Presse notes (7/21).