Abstract
There are many types of influenza viruses, which cause
illness in a variety of birds and mammals. New strains are
constantly evolving, causing seasonal influenza epidemics
in humans. This article provides information about
influenza and influenza viruses, and the three influenza
pandemics of the twentieth century. Pandemic influenza
is differentiated from avian influenza, which is a viral
disease that primarily infects birds. The current outbreak
of avian influenza H5N1 in poultry flocks across the world
is unprecedented in its spread. Human infection with avian
influenza is rare and for most strains the symptoms are
usually mild. A notable exception is HN51, where almost
60 per cent of the currently recorded 251 human cases
have died. While the risk of a pandemic occurring in the
current circumstances is unknown, there is a high level of
concern worldwide.
