Influenza is a contagious illness caused by influenza viruses. Influenza A viruses are designated on the basis of the antigenic relationships of the haemagglutinin (HA) and neuraminidase (NA) proteins. Of these only Hl, 2 or 3 and NI or 2 are known to infect humans. Outbreaks of influenza usually occur in colder months. The main symptoms are an abrupt onset with high fever, headache, extréme tiredness, dry cough, sore throat, muscle and bone aches. Only symptomatic treatment is indicated in otherwise healthy persons without complications. Avian influenza viruses háve various combinations of 16 haemagglutinins and 9 neuramini-dases. They cause illness only in birds and other animals that háve epithelial cells in their airways that bear receptors enabling adhesion and replication of avian flu viruses. There are no such cells in humans. Human infection is exceptional, resulting from direct contact with infected birds with a high infectious dose. Anti-viral drugs - neuraminidase inhibitors- may be recommended for the treatment of both human and avian influenza. Antiviral treatment lasts for 5 days and must be started within 2 days of illness when the viral replication culminates. A later initiation of antiviral treatment has no effect on the course of influenza.

        Key words: human influenza, avian influenza, haemagglutinin, neuraminidase, neuraminidase inhibitors