This transmission electron micrograph (TEM), taken at a magnification of 150,000x, revealed the ultrastructural details of an avian influenza A (H5N1) virion, a type of bird flu virus which is a subtype of avian influenza A. At this magnification, one may note the stippled appearance of the roughened surface of the proteinaceous coat encasing the virion.
Although this virus does not typically infect humans, in 1997, the first instance of direct bird-to-human spread of influenza A (H5N1) virus was documented during an outbreak of avian influenza among poultry in Hong Kong. The virus caused severe respiratory illness in 18 people, of whom, 6 had died. Since that time, there have been other instances of H5N1 infection among humans.
During August to October, 2004, sporadic human cases of avian influenza A (H5N1) were reported in Vietnam and Thailand. Since December, 2004, a resurgence of poultry outbreaks and human cases has been reported in Vietnam. On February 2, 2005, the first of four human cases of H5N1 infection from Cambodia was reported. On July 21, 2005, the first human case of H5N1 in Indonesia was reported, and since then Indonesia has continued to report human cases in August, September, and October, 2005.
Credit: CDC/ Cynthia Goldsmith; Jackie Katz