Scientists studying bird flu strain that killed two men in China says that virus could be harder to track

Scientists taking a first look at the genetics of the bird flu strain that recently killed two men in China said today that 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, at several research institutes around the world, said the H7N9 virus seems troubling because it can generate no symptoms in poultry while seriously sickening humans.

They said the virus, previously known to have infected only birds, appears to have mutated, enabling it to more easily infect other animals, including pigs, which could serve as hosts spreading the virus more widely among humans.

The findings are preliminary and need further testing. In the meantime, the scientists are urging Chinese veterinary authorities to widely test animals and healthy birds in affected regions to detect and eliminate the virus before it becomes widespread.

In addition to causing two deaths in Shanghai, the virus also seriously sickened five other people in two eastern provinces in the strain's first known infections of humans.

Those regions stepped up measures this week to guard against the spread of the disease, calling on hospitals to report severe pneumonia cases with unknown causes and schools to monitor for fevers.