How is the Asian H5N1 strain of avian influenza spreading from place to place?
Healthy birds become infected from direct contact with sick birds, or contact with areas or objects contaminated by sick birds. Much of the spread in Asia is probably a result of movement of live birds to markets. Wild birds may also have the virus but do not always get sick. If they are infected but not sick, they might be able to spread the virus to new areas when they migrate.
