A new strain of avian influenza (bird flu) that has killed 22 people so far in China is "one of the most lethal influenza viruses" that scientists have ever encountered, according to Keiji Fukuda, an official with the World Health Organization (WHO). Fukuda also said of the new H7N9 virus strain that "when we look at influenza viruses, this is an unusually dangerous virus for humans," as Reuters reported today.

The comments come on the same day as the first reported case of H7N9 in a person outside China, where all 108 confirmed cases have occurred since the outbreak first began in late March. Late Wednesday afternoon Taiwan time, the Taiwan Centers for Disease Control reported its first confirmed human diagnosis of H7N9, in a man who had recently returned from China and developed symptoms three days later. That man is currently in severe condition and being treated in a contained room, according to Taiwan's CDC. Symptoms of H7N9 include severe cough and fever, which can progress to severe pneumonia and eventually death. So far, the virus appears to have been concentrated in elderly men, but scientists still aren't sure why.

Unfortunately, the initial days of an international scientific investigation into bird flu in China, led by the World Health Organization, haven't answered many key questions yet — such as whether or not the virus has the potential to be transmitted between humans. Typically, bird flu is transmitted only from birds to humans who have been in direct contact with them, limiting the pandemic potential of the virus. But a large portion of the new H7N9 cases in humans have reportedly occurred in people who haven't been around birds. Part of the WHO's scientific investigation has been hampered by the fact that birds infected with the virus seem to suffer less severe forms of illness than human patients, and don't display visible symptoms. The goal is to trace the virus to its sources and contain it, but scientists agree that no matter how quickly that process takes place, there will likely be at least a few more human cases to emerge.