China's deadly new H7N9 bird flu virus may be harder to track than predecessors, scientists say Workers unload chickens from a container at a wholesale market on April 3, 2013, in Shanghai, China. / AP Beijing Scientists taking a first look at the genetics of the bird flu strain that recently killed two men in China say the virus could be harder to track than its better-known cousin H5N1 because it might be able to spread silently among poultry without notice. The scientists said Wednesday that the H7N9 virus seems troubling because it can generate no symptoms in poultry while seriously sickening humans. Dr. Masato Tashiro, a WHO scientist studying the virus' genetic data, says the virus also appears to have mutated into a form that enables it to more easily infect animals such as pigs, meaning they could serve as hosts that spread the virus more widely among humans. H7N9 is previously known only to have infected birds. The preliminary findings need further testing.