|
Figure 3. Hemagglutinin subtypes—H1 to H15—have been found in
various combinations among human beings, mammals and birds. All 15 subtypes
are present in avian species, mostly aquatic birds. Five subtypes have been
found in human beings, but the H5 and H9 subtypes have not established lineages
in our species. Similarly, H4 and H7 have been isolated in seals, and H4
and H9 have been isolated in swine, but these subtypes have not yet established
lineages in these animals. Aquatic birds usually don’t become sick from the
virus, and they are believed to be the living repositories for all subtypes
of the type A viruses. |
