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A review and update about a new zoonosis, as it is the Avian Influenza or "poultry grippe" has been made. This disease is endemic in the Southeast of Asia and continues at present time, being active in Vietnam and Tailand. We have considered the Natural History of the Avian Influenza and specifically the late epidemies, starting from the one in 1997 in Hong Kong, in which an Orthomyxovirus type A, subtype H5N1, broke the interespecies barrier. A health analysis is made, both for the present moment and the future, about the possibility of a World pandemic flu, originated by the mentioned Orthomyxovirus type A, agent of the Avian Influenza of highly virulent specificic virus strain pathogenic for men. The most favourable fact, among others, to deny the possibility of a future pandemic flu is the stability of H5N1 strain in both epidemics of poultry in Hong Kong and in the Southeast of Asia.

Avian influenza affects most types of birds and occurs in epidemics on poultry farms. The fatal disease is named "highly pathogenic avian influenza" and is caused by influenza A virus subtypes H5 and H7. The natural reservoir is the migratory waterfowl that occasionally infects domestic poultry. In 1997 in Hong Kong, 18 persons were infected and 6 of them died. At the end of 2003 and the beginning of 2004, avian influenza H5N1 infected numerous farms in several South-Eastern Asian countries. The virus was transmitted to humans in close contact with infected birds. A total of 34 persons were infected and 23 of them died. There is currently a considerable concern about the H5N1 avian influenza that has infected humans: the high virulence, evolution rate, the possibility of recombination with other influenza viruses, how H5N1 variants that infect humans or different approaches to the development of influenza vaccines.

Severe acute respiratoru syndrome (SARS) is a new disease that caused large ourbreaks in several countries in the first half of 2003, resulting in infection in more than 8.000 people and more than 900 deaths. The disease originated in southern China and a novel coronavirus (SARS CoV) has been implicated as the causative organism. We present an overview of the etiology, clinical presentation and diagnosis, based on the current state of knowledge derived from published studies and our experience in the National Microbiology Centre. Influenza is a zoonosis. This appreciation of influenza ecologyfacilitated recognition of the H5N1 'bird flu' incident in Hong Kong in 1997 in what was considered to be an incipient pandemic situation, the chicken being the source of virus for humans and. The current outbreak of avian influenza in South East Asia has resulted in a small number of human deaths. These findings highlight the importance of systematic virus surveillance of domestic poultry in recognizing changes in virus occurrence, host range and pathogenicity as signals at the avian level that could presage a pandemic.