At least 40 people have died and more than 1,000 have tested positive for swine flu since the beginning of this year in a western Indian state popular with foreigners, authorities said. Last year around 1,100 people died and 15,000 were infected across India by the highly contagious A H1N1 virus that spreads from human-to-human. Cases spike in the winter months of December and January in the west and north of the country including in Rajasthan and in New Delhi.

Swine influenza is an infection caused by any one of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) is any strain of the influenza family of viruses that is endemic in pigs. As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3

The Swine flu was seen in humans in Mexico in 2009

The Swine flu was initially seen in humans in Mexico in 2009, where the strain of the particular virus was a mixture from 3 types of strains. Six of the genes are very similar to the H1N2 influenza virus that was found in pigs around 2000.

Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human flu, often resulting only in the production of antibodies in the blood. If transmission does cause human flu, it is called zoonotic swine flu. People with regular exposure to pigs are at increased risk of swine flu infection.

Direct transmission of a swine flu virus from pigs to humans is occasionally possible. In all, 50 cases are known to have occurred since the first report in medical literature in 1958, which have resulted in a total of six deaths. Of these six people, one was pregnant, one had leukemia, one had Hodgkin's lymphoma and two were known to be previously healthy. One of these had unknown whereabouts.

Doctors must plan a door-to-door campaign

Despite these apparently low numbers of infections, the true rate of infection may be higher, since most cases only cause a very mild disease, and will probably never be reported or diagnosed. Authorities in Rajasthan, famous for its deserts and palaces, have told doctors they must seek permission before going on leave and plan a door-to-door campaign to detect infected patients. 

Health officials have also launched an awareness campaign to sensitise people about symptoms, precautions and treatment, and have screened more than 5,100 people."Total deaths are 40 and positive cases are 1,036 as from January 1 to 17 in Rajasthan. One of the deaths occurred on Thursday," according to a statement by the Rajasthan health department.

One high-profile victim in Delhi this week was Amit Shah, a top aide to Prime Minister Narendra Modi, who was admitted to hospital with the virus. Rajasthan's Jodhpur district recorded the highest death toll with 16 fatalities and 225 people testing positive.No travel advisory has been issued however.