People infected with the virus show symptoms similar to common cold such as runny nose, cough and fever, but there is no vaccine for it. No serious effort has been made to search for one till now as there have been very few cases so far. Only 50 cases of human swine flu have been reported since 1958, said Christopher Olsen, a virologist with University of Wisconsin, the US, in his 2007 study published in Clinical Infectious Diseases.
Alert in India
The swine flu has not affected India so far. But the health authorities are not taking chances. About 100 doctors from the Central Health Services have been deployed at airports, said Vineet Choudhary, joint secretary with the Union health ministry.
All international travellers are given a form to fill in which they are asked about their travel history. People with symptoms of flu are taken to hospitals and samples are taken with throat swabs, said Choudhary.
Government officials said they are also stocking up Tamiflu antiviral pills, found effective in treating swine flu.
Virus has human flu strain
The source of the virus is not known. But Hana Weingartl from the National Centre for Foreign Animal Disease, Canada, has theorized the virus originated from the Spanish Influenza virus (also an H1N1 strain) that claimed 50 million lives in the 1918 pandemic. The virus probably infected pigs at that time, Weingartl said in her study published in May 2009 issue of Journal of Virology .
There is no explanation how the disease has surfaced again after more than 90 years. The La Gloria residents blamed it on the pollution from a nearby pig farm owned by a US-based multinational firm. Many of them were suffering from respiratory illness for several months. But the authorities hushed it up and did not probe the matter.
A 2005 study published in Nature predicted such an outbreak after bird flu virus H5N1 was detected in pigs in Java, Indonesia. Chairul Nidom, a virologist with Airlangga University in Java, said this was a cause for concern as pigs can harbour both bird and human flu virus. The different strains mix and rearrange their gene sequences to emerge as a new viral strain to infect humans, Nidom said. His words proved prophetic.
The swine flu A(H1N1) virus is a combination of bird flu, human flu and two strains of swine flu viruses, said Shashi Khare, a microbiologist with National Institute of Communicable Diseases, Delhi. She said since the virus has a component of the human flu virus, it attaches itself easily to human cells. It attacks the upper respiratory tract and spreads fast through air from person to person. The bird flu in 2003 did not affect people as much because the virus attacks the lower respiratory tract and did not have human flu virus component in it, Khare explained.
Canada, meanwhile, has reported the first case of reverse transmission of the A(H1N1) virus from humans to pigs. As many as 220 pigs were infected by a farm worker who became ill during a recent trip to Mexico. who said the farm has been quarantined.
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