New research on the origins and spread of HIV may have revealed precisely how the virus entered the United States, and what difficulties could lie ahead in creating a vaccine.

Michael Worobey, an assistant professor of ecology and evolutionary biology, was part of an international team that conducted a study indicating that HIV entered the United States in 1969, probably through a single person arriving from Haiti.

Results of the study, the first research to definitively pinpoint when HIV originally entered the U.S. and how it spread from a common ancestor, were published last week in Proceedings of the National Academy of Sciences.

HIV was present in apes as SIV, Simian Immunodeficiency Virus, for thousands, and possibly millions, of years, Worobey said, but in humans, “”HIV is a 20th-century phenomenon.””

The current theory is that unsafe hunting practices, combined with increased human mobility in and out of central Africa, where the disease originated, is what made HIV a global issue. The first case was reported in 1930.

Currently, there are several breeds of HIV. All strains have a common ancestor, Worobey said, but mutations happen all the time.

Subtype C is the one most common in Africa and India.

“”Every individual has a slightly different variant,”” he said.

The most common type in America, HIV-1 group M subtype B, was the first to be identified and is the most widely spread version of the virus outside Sub-Saharan Africa. It is also the same type that came from Haiti.

The researchers analyzed five blood samples from Haiti immigrants, some of the earliest-known carriers of HIV in the U.S. They then compared those blood samples with more recent blood samples of 117 HIV subtype B patients, Worobey said.

Using statistical methods, the team determined the likelihood of different mutation paths of HIV, finding that the probability of the virus coming from Haiti was 99.8 percent, versus a .003 percent of it stemming directly from Africa.

“”There have been some interesting turning points,”” Worobey said. “”This study is the

clearest picture of how the virus has spread.””

Although the difference in the types of HIV provided the means of tracking the disease, it also makes it more difficult to vaccinate.

Vaccines for one version may prove useless on others, and the longer HIV is around, the more it can mutate, further enhancing the problem.

Locally, the Pima County Health Department began a program to deal with HIV in 1987 with a staff of two.

“”We now have a staff of over 20,”” said Susan Eisen, the department’s HIV program coordinator. “”We test between 3,000 and 4,000 people a year.””

With the recent advent of a 20-minute HIV test, the amount of resources for testing and counseling continues to increase, Eisen said.

“”It used to take weeks to find out,”” she said.

According to the World Health Organization, approximately 39.5 million people live with HIV, with 4.3 million new infections in 2006. More than 1.2 million people in the U.S. live with HIV.