avian influenza

a disease of poultry and other birds caused by strains of influenza A virus. The severity of the disease depends on the strain of virus involved: H5N1 is particularly deadly (causing fowl plague (or pest), with a mortality approaching 100%) and very contagious, being spread between domestic flocks by wild birds. This virus is not easily transmissible to humans, requiring close contact with infected birds or their faeces. The first human cases of H5N1 infection (‘bird flu’) were reported in 1997 and restricted to Hong Kong: 18 people were infected, six of whom died. The most recent outbreak was more widespread. It started in January 2004 after an outbreak of H5N1 among poultry in Korea quickly spread throughout southeast Asia and beyond; by late November 2006 a total of 258 human cases (with 153 deaths) had been reported worldwide. Although the disease has not yet appeared among humans in Europe, wild and imported birds with H5N1 infection have been reported and rigorous efforts have been made to isolate or vaccinate domestic flocks considered at risk. If the human form of the disease were to become widespread, through bird-to-human transmission, there are fears that strains transmissible between humans could evolve, possibly resulting in a pandemic of a new form of influenza.