SWINE FLU - PAST AND A CONCERN FOR FUTURE
Dr. Anil M. Mane*
Influenza viruses are viruses which cause mild to severe respiratory infections. They belong to the family Orthomyxoviridae and are classified into three types, A, B, and C, based on the variation in the structure of their surface proteins. Influenza A infects many mammals and aquatic birds and is the most common and the most severe pathogen among the three types. Influenza B is almost exclusively a human pathogen, whereas Influenza C causes milder disease and is less common than the other types. Influenza A viruses are further classified into subtypes based on the surface glycoproteins hemagglutinin (1-16 subtypes of HA) and neuraminidase (1-9 subtypes of NA). At a given time, the most common subtypes circulating in' human populations are H1N1 and H3N2. The last century witnessed three Influenza pandemics - the Spanish Flu caused by H1N1 (1918-1920), the Asian Flu caused by H2N2 (1957-1958), and the Hong Kong Flu caused by H3N2 (1968-1969). The first pandemic of the present century was caused by the 2009 H1N1 Influenza A virus, also known as HINlpdm of the H1N1 subtype. This virus was formerly also known as swine flu as it contains a unique combination of gene segments from human, avian, and segments from the so-called triple reassortant swine viruses that emerged in North American pig populations in the late 1990s. No major Influenza virus activity was reported in pigs when the outbreak was recognized in humans, however, pigs can be experimentally and naturally infected with 2009 H1N1 viruses, resulting in mild respiratory infection.
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