Following an incubation period of usually a few days (but rarely up to 21 days), depending upon the characteristics of the isolate, the dose of inoculum, the species, and age of the bird, the clinical presentation of avian influenza in birds is variable and symptoms are fairly unspeciÞc (Elbers 2005). Therefore, a diagnosis solely based on the clinical presentation is impossible.

Avian Influenza Virus Infections in Humans: Avian influenza virus strains have only recently been identified as the cause of human disease. For most of these, the clinical manifestations in humans are mild. In 1996, an avian H7 virus was isolated from a woman with conjunctivitis (Kurtz Avian Influenza Virus Infections in Humans 165 1996). In 1999, a H9N2 strain was isolated in Hong Kong from two children with mild influenza symptoms (Peiris 1999, Horimoto 2001).

Transmission of avian influenza viruses to humans, leading to the development of clinically overt disease is a rare event (Table 3). Given the potential exposure of millions of people to HPAIV H5N1 in South East Asia, the actual number of documented human cases, although steadily growing over the past years, must still beconsidered as being comparatively low (http://www.who.int/csr/disease/avian influenza/country/en).