H5N1

There are 16 types of flu virus, depending upon the Hemagglutinen structure ... and H1, H2 and H3 are "human" viruses. H5 is (normally) a bird virus, but can attack pigs ... and it may mutate! The structure of the virus is also influenced by Neuraminidase protein. It's the H - N combination that identifies the virus: Now, China (which has had the deadlier H5N1 virus for some time) fears the worst: "Inside China, H5N1 has been existing for some time, so if there is really a reassortment between H1N1 and H5N1, it will be a disaster"