The researchers, Michael Worobey and team from the University of Arizona, say the finding will help in the development of an efficient vaccine against aids. The researchers say they studied blood samples of five patients who were among the first recognized aids victims; all of whom had immigrated to the us. They compared the samples with those of another 117 aids patients from different parts of the world and traced back the family history of the virus. The study appeared online on October 30, 2007 in the journal Proceedings of the National Academy of Sciences.

But many experts say the results might not be useful in developing a vaccine against the deadly virus. So far, an effective vaccine has been elusive as the character of the virus changes frequently from place to place.

“There are eight major subtype of HIV-1 in addition to the existing recombinants within the subtype which are accumulating and these type of changes are increasingly occurring as days progress which poses a great challenge to vaccine development” says Smarajit Jana, member of the National Aids Council in Delhi.

He says, “When an epidemic spreads, it goes to 3-4 different directions, not just to one area. So, a lot more archival samples have to be tested to get the truth.’ In India, the major circulating stain is the subtype C and scientists say the vaccine developed on the strain collected from one country may not be effective in other countries because of the very nature of the virus which is not predictable and changes rapidly.

Meanwhile, the report has sparked off a controversy outside the us . Haitians see it as a ploy to vilify the country. “This report is just an extension of a larger campaign by the us to squash the people’s movement in Haiti,’ said Noluthando Williams, a Haitian activist.