Published on National Geographic, by Amitabh Avasthi, October 29, 2007.
an excerpt: … The new study appears online this week in the journal Proceedings of the National Academy of Sciences.
Root of the Epidemic: HIV is commonly transmitted through tainted blood transfusions, dirty needles, and unprotected sex. Infections often lead to a life-threatening condition in which the body’s immune defenses are systematically disabled.
Two species of HIV can infect humans—HIV-1 and HIV-2. The former is more virulent, more easily transmitted, and accounts for the lion’s share of global HIV infections. HIV-2 is less infectious and is largely confined to parts of Western Africa.
Based on differences in one of the nine genes that make up the virus, HIV-1 is placed in three major groups. The most prevalent, Group M, has eight geographically distinct subtypes …
… Page 2: Worobey and his colleagues looked at subtype B. Though it is found mainly in North America and Europe, the strain is present in the most number of countries.
The researchers analyzed tissue samples from five Haitian AIDS patients collected in 1982 and 1983. All five had then recently immigrated to the U.S. and were among the first recognized victims of AIDS.
A family tree constructed from the HIV-1 genes of the five Haitians and subtype B gene sequences from 19 other countries place the Haitian virus at the root of all branches … (full text).