What is novel H1N1 (swine flu)?
Novel H1N1 (referred to as “swine flu” earlier) is a new influenza virus causing illness in people. This new virus was first detected in people in Mexico and United States in April 2009. This virus is spreading from person-to-person worldwide, probably in much the same way that regular seasonal influenza viruses spread. On June 11, 2009, the World Health Organization (WHO) signaled that a pandemic of novel H1N1 flu was underway. India reported its first case on 16th May 2009 in an adult male returning from the US.  

Why is novel H1N1 virus sometimes called “swine flu”?
This virus was originally referred to as “swine flu” because laboratory testing showed that many of the genes in this new virus were very similar to influenza viruses that normally occur in pigs (swine) in North America. But further study has shown that this new virus is very different from what normally circulates in pigs.

It has two genes from flu viruses that tend to circulate in pigs in Europe and Asia and bird (avian) genes and human genes. Scientists call this a "quadruple re-assortant" virus.

Is this the first time that Swine Flu has appeared around the world or have we seen it earlier?
Historical information on the global epidemiology of this disease is incomplete; however, some information is available. Classical H1 swine influenza viruses (SIVs) were first detected in North America in the 1930s. Re-assortment of genes from swine, avian, and human viruses have occurred periodically, and triple swine, avian, and human H1N1, H1N2, and H3N2 re-assortant viruses have been circulating in swine since at least 1998, especially in North America. These viruses have also been detected in Asian swine populations.

There have been sporadic (2-3 per year) incidents of transmission of triple re-assortant swine viruses and other SIVs to humans (e.g. H1N1, H1N2), but with no previously reported sustained human-to-human transmission. The current circulating H1N1 virus appears to be a further re-assortant of the triple reassortant swine viruses mentioned above. The gene composition of this virus, in addition to historical data, clearly indicates that SIVs are very prone to re-assorting with other SIVs, as well as with avian and human influenza viruses.