HIV said to differ in blood, semen

CHAPEL HILL, N.C. — HIV-infected blood and semen hold different versions of the virus that causes AIDS, a finding that could help researchers working to find an effective vaccine, according to a new study by researchers at UNC-Chapel Hill.

The study compared the genetic makeup of the virus in blood and the one in semen collected from a group of infected men in Malawi and analyzed the gene coding for envelop, or Env, a major surface protein of the virus, in the samples.

"If everything we know about HIV is based on the virus that is in the blood, when in fact the virus in the semen can evolve to be different, it may be that we have an incomplete view of what is going on in the transmission of the virus," said Dr. Ronald Swanstrom, senior author of the study and professor of biochemistry, microbiology and immunology at the UNC School of Medicine.

Published last week in the Public Library of Science Pathogens online journal, the study revealed that HIV-1, the most common strain of the virus and the one most likely to cause AIDS, has different genetic patterns in blood and semen. Researchers mapped hundreds of viruses in the semen and blood of the men using single genome sequencing, an expensive and labor-intensive technique.

"It is an achievement they were able to do with 16 men," said Dr. Stuart Shapiro, program officer with the preclinical research and development branch at the Center for HIV-AIDS Vaccine Immunology, which is funded by the National Institutes of Health. Shapiro said he doesn't think the results would have changed if researchers could have mapped the virus in more men.

Variations of HIV in blood and semen have been suggested by researchers, but the study has taken a first step in proving that such genetic differences exist, he said.

Semen is the source of the virus in a majority of transmissions for HIV-1, so an understanding of the biology of the virus in the seminal tract is important to understanding how the virus is transmitted and changes once inside the body, the report said.

"It compels us to ask the question, what is making this virus different?" Swanstrom said. "Is there anything about the biology that is important to understand?"

The reasons the virus changes in the seminal tract are still unknown. The two strains have different genetic makeup, but researchers don't think it affects transmission rates or the lethality of the virus, Shapiro said.

"I don't think this would suggest any behavioral change," he said. "People should already be engaging in practicing safe sex."

It is estimated that more than 1 million people are living with HIV in the United States and that more than half a million have died after contracting AIDS, according to AVERT, an international AIDS charity. In 2008, more than 900,000 people were living with HIV and/or AIDS in the southeastern Africa nation of Malawi.