Infectious diseases are the major cause of health concern claiming a large number of precious lives worldwide every year. The influenza virus is one among them and it can infect both human beings and animals notably pigs, birds, horses etc. Swine flu is an infection caused by a virus, influenza A (H1N1), a subtype of influenza A virus and it is the most common cause of human influenza with some strains found to be endemic, causing influenza like illness and seasonal influenza in human beings. World Health Organization (WHO) has declared swine flu as a pandemic and this took a heavy toll of human life across the globe. Scientists across the world are battling to develop a potential vaccine against the newly emerged virus. As of now, antiviral drugs like oseltamivir and zanamivir are in use for treatment. More over, healthy and hygienic practices also can prevent the spread of this virus. In this paper, an attempt has been made to discuss the classification and biological origin of influenza A (H1N1). In addition to this, the study throws light upon the epidemiology, treatment and prophylaxis of influenza A (H1N1) infection. Researchers are actively engaged in developing a potent vaccine against this virus and public is also more curious to know the developments. People are not that much aware about the mode of spread and prevention about this infection. An effective method to prevent this infection is by educating people about its manifestations and possibilities of complete cure by medication and give them a relief.

Influenza as a disease of pigs was first recognized during the Spanish influenza pandemic of 1918-19 (Kilbourne, 2006). Veterinarian J S Koen was the first to describe the illness, observing frequent outbreaks of influenza in families followed immediately by illness in their swine herds and vice versa (Easterday, 2003). Influenza virus was first isolated from pigs in 1930 by Shope and Lewis (1931) and the first isolation of a swine influenza virus from a human occurred in 1974 (Smith, 1976).

H1N1 swine flu is still rampant in the world killing people, although it is on the decline in some parts. As on April 20, 2010, about 17,798 (WHO) swine flu deaths were reported worldwide. As per the data available from Ministry of Health and Family Affairs, Government of India, 1,482 deaths were reported. The WHO reported that the H1N1 strain is the dominant form of influenza globally, but some seasonal strains are starting to emerge in China and Africa. The US is one of the hardest hits with more than 80 million Americans infected with swine flu and about 11,000 people have died.

Influenza A H1N1 is a circulating seasonal viral infection that became pandemic in 1918-19. The present pandemic is being caused by a new subtype of Influenza A H1N1 which has reassorted with antigenic segments from American swine, Eurasian Swine, avian and human influenza virus.Three types of influenza viruses are known. They are influenza A, B and C. Human beings are affected by all these three viruses. In lower animals and birds, influenza A viruses are of primary concern. Influenza A virus causes infection in humans around the year and is responsible for most of the seasonal epidemics and pandemics. Influenza B causes sporadic and less severe outbreaks, whereas type C causes mild respiratory illness.

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