Swine flu and the current influenza A (H1N1) pandemic in humans: A review

Swine influenza (swine flu) is a highly contagious and an economically important disease of pigs caused by type A influenza viruses of the family Orthomyxoviridae. Mainly H1N1, H1N2, H3N2 and H3N1 subtypes of influenza A viruses are endemic in pig populations worldwide. Pigs can also be infected by human and avian influenza viruses and, acting as ‘mixing vessels’ for them, can give rise to novel reassortants. Human infections with swine flu H1N1 viruses have been earlier reported to be rare. The current swine origin novel influenza A (H1N1) virus is a quadruple-reassortant, which has gene segments from both North American and Eurasian swine lineages along with human and avian influenza viral genes. The virus has gained the capability for human to human spread without affecting pigs. This novel H1N1 virus is causing pandemic infection in humans in several countries around the world, with WHO updated figures as on 6 July 2009 standing at 429 deaths out of 94,512 affected persons in 135 countries. Vaccines, in addition to other protective measures, are one of the most valuable ways to protect people from the current influenza A (H1N1) pandemic. However, presently there are no vaccines against this newly evolved virus. Hence, it is important to develop a vaccine against the circulating virus strain, using the strain itself or exploiting the technique of reverse genetics for developing a novel vaccine candidate. The chemotherapeutic and chemoprophylaxis drug of choice is oseltamivir. Strict implementation of vigilance and monitoring, personal hygiene and quarantine has been considered crucial in prevention and control of current ‘swine flu’ pandemic. Extreme genetic variations exhibited by the influenza viruses are the hallmark, which make the disease difficult to be controlled. This review highlights the flu virus, especially swine flu virus, its epidemiology, viral reassortments and evolution, disease in pigs and man, diagnosis, interspecies transmission, preventive measures and the current pandemic situation in humans.