TUESDAY, Oct. 30 (HealthDay News) -- New research into the genetic history of HIV suggests that the virus that causes AIDS stopped in Haiti during the middle of the last century, prior to reaching the United States.

The findings are unlikely to help scientists discover better treatments for AIDS, but they could provide insight into how HIV evolves and moves from place to place, said Michael Worobey, a professor in the University of Arizona's Department of Ecology and Evolutionary Biology and co-author of a study released Monday.

"It matters when these events occurred and how often colonizations of new locales occur," he said. "That helps us predict the future complexity of the HIV pandemic."

The study findings about the spread of HIV are "definitive," added Dr. Beatrice Hahn, a professor in the University of Alabama at Birmingham's departments of medicine and microbiology. Hahn, who studies how the virus developed, said the next step in research is to go "further back in time" and use old blood samples from central Africa to understand more about the early days of AIDS.

Scientists are certain that the AIDS virus developed somewhere in Africa after a virus jumped from monkeys to humans. But there are still questions about the history of HIV and how it incubated in Africa before moving on to the rest of the world.

In the new study, Worobey and colleagues studied a strain of the AIDS virus known as subtype B, which commonly affects people in many countries, including the United States. The researchers tried to figure out how the virus traveled by studying blood samples of Haitian immigrants to the United States who were among the first in the country to be diagnosed as suffering from AIDS.

"For the last few years, we've been thinking it would be good to try to collect and analyze as many archival human samples as possible," Worobey said. "We can travel back in time and look directly at the viruses that were circulating at early time points."

The findings were published this week in an online edition of the Proceedings of the National Academy of Sciences.

After using genetic techniques to study the evolution of the virus, the researchers came to believe that the AIDS strain moved from Africa to Haiti at some time during the mid-1960s. They think it circulated in Haiti for perhaps a few years before moving on to the United States in about 1969.

Doctors didn't begin picking up on the existence of the virus in the United States until 1981, when they noticed that some gay men were developing unusual diseases. "That leaves a 12-year period between when we think it came in, and people realized there was something new," he said.

What could explain that? It's possible that the virus was around and making people sick for a decade or more, but the number of people infected may have been tiny, Worobey said. After all, it can often take 10 to 12 years for someone to become ill with AIDS after being infected by the virus, he said.

Going back even earlier, some scientists suspect that AIDS stalked Africa since the 1930s. "It's not that surprising that it circulated for 30 years before we have any hard evidence of it," Worobey said. "In Africa, most people die of tuberculosis when they have AIDS, and that adds a whole layer of fog" to detecting HIV disease, he said.

What now? Scientists could use the findings about Haiti as they try to develop vaccines, Worobey said. The AIDS strain in question "has a deeper history in Haiti than in all these other countries (that it traveled to). Its genetic diversity is more extensive, and that should be considered when either testing or designing subtype B vaccines in the future."

More information

There's more on the history of HIV and AIDS at the U.S. Food and Drug Administration.

TUESDAY, Oct. 30 (HealthDay News) -- Among prostate cancer patients undergoing a high-tech form of radiation therapy, exposure to a higher amount of radiation over a shorter time span poses no added risk for impaired sexual function, new research reveals.

"For men getting a high dose of radiation in a shorter amount of time than is typical -- meaning getting higher doses per day for fewer days -- a loss of sexual function is the chronic side effect that concerns most," noted study co-author Dr. Eric Horwitz, a clinical director in the department of radiation oncology at Fox Chase Medical Center in Philadelphia.

"But we found that sexual function wasn't any worse than when patients got radiation in the conventional high-dose way," he said.

Horwitz and lead author Mark Buyyounouski, also at Fox Chase, were expected to present their team's findings at the annual meeting of the American Society for Therapeutic Radiology and Oncology, in Los Angeles.

The finding comes on the heels of work conducted at Fox Chase last year. That study indicated that high-dose radiation should be considered the first line of attack in combating prostate cancer, given that it appears to be the most effective way to limit the disease's spread.

The team focused on a form of radiation therapy called intensity-modulated radiation therapy (IMRT). According to the American Cancer Society, IMRT is a cutting-edge, 3-D form of high-dose radiation therapy. The treatment is delivered by a computer-controlled machine that moves around the patient to target diseased tissue while avoiding healthy tissue, thereby allowing for the safer use of higher doses of radiation.

In the current study, Horwitz and his colleagues tracked the IMRT radiation treatment outcomes of 155 men diagnosed with intermediate to high-risk prostate cancer.

Half the men were assigned to receive 2 Gray (Gy -- a measurement of radiation) in 38 sessions spread over seven and a half weeks.

The other half were exposed to 2.7 Gy in 26 sessions spread over just five weeks.

All the patients then completed questionnaires regarding treatment side effects six months, 12 months, and 24 months following radiation.

Older age, as well as poor sexual function prior to radiation, did increase the risk for sexual impairment after radiation treatment, the researchers said. However, they report no appreciable difference in sexual function between the men receiving the shorter course/higher dose regimen or the more conventional regimen.

"The key to curing more prostate cancer is to give higher does of radiation," observed Horwitz. "And over the last few years, more and more men have been getting higher dose radiation, because the radiation oncology community knows that dose matters and that low dose radiation is just not effective compared to high dose. And this study shows that we have the ability to give these high doses in different ways, and in all these ways, men do very well."

Horwitz said he and his colleagues plan to take the current research to the next level.

"We will build on this experience and go with even higher doses," he said, "to see how that impacts not only sexual function but urinary and bowel function as well."

Dr. Peter T. Scardino is chairman of the department of urology and head of the Prostate Cancer Program at the Memorial Sloan-Kettering Cancer Center in New York City. He described the finding as a small but important step toward developing shorter course/higher dose radiation therapies.

"This is the trend nowadays," said Scardino. "This is where this is going: toward a time when perhaps we will be giving radiation therapies all in a single day."

"Animal studies have already indicated that you may be able to achieve as much or more with a single dose of radiation than with a protracted course," Scardino noted. "So, the big question is, are you going to find more complications as a result of this kind of a shift in dosage? Now, cutting back from seven and a half weeks to five weeks is a slight move in this direction, but they found no difference in sexual side effects, and that's valuable. And I certainly think we'll be seeing a lot more research in this area."

More information

There's more on radiation therapy for prostate cancer at the American Cancer Society  .

WEDNESDAY, Oct. 17 (HealthDay News) -- A test to detect human papillomavirus (HPV) -- which causes most cervical cancers -- was far better than the standard Pap smear at catching malignancies, two new studies show.

What's unclear, however, is whether or not the HPV test should take the place of Pap testing, because it can have a slightly higher false positive rate, and it's not as effective in younger women.

"There are still many questions related to the use of HPV testing as the primary screening test," said Debbie Saslow, director of breast and gynecologic cancer for the American Cancer Society. "At this time, HPV testing alone (without a Pap test) is not FDA-approved as a primary screening test, so that approach is not recommended by the American Cancer Society."

But, Saslow pointed out, "The most important message remains unchanged: Women should be screened using one of three options: a conventional Pap test, liquid Pap or Pap plus the HPV test. For women who have access to HPV testing, the HPV test offers added benefits over [Pap tests] alone."

Pap tests have been the standard screening test for cervical cancer for the past 60 years. More recently, the liquid-based or thin-smear Pap test was developed, and it was initially thought that this newer technology would offer significant advantages over the traditional Pap test. However, studies haven't conclusively found a significant benefit to the newer test. Because most cervical cancers are caused by HPV, the test to detect HPV infection is also an option for screening in addition to the Pap test.

The most recent research comparing these screening tests appears in the Oct. 18 issue of the New England Journal of Medicine. The first study, done in Canada, compares the use of conventional Pap alone to the use of the HPV test alone.

The study included more than 10,000 women between 30 and 69 years old who were randomly assigned to one of the tests. The HPV test detected 94.6 percent of the abnormal growths that can lead to cervical cancer, while the Pap test found only 55.4 percent of these growths. Women who had an abnormal result were referred for further testing. If both Pap and HPV were used together, 100 percent of the abnormal growths were found. The false-positive rate for HPV was only 2.7 percent higher than the rate for Pap smears, according to the study.

"Even though Pap has worked, we have a test that's better than Pap, and in the coming years, we can switch to HPV and possibly screen every three or maybe even every five years and get the same level of protection," said study author Dr. Marie-Helene Mayrand, an assistant professor of obstetrics and gynecology and social and preventive medicine at the University of Montreal. Mayrand was a doctoral candidate at McGill University in Montreal at the time of the study.

The second study, done in Sweden, included more than 12,000 women in their 30s who were randomized to receive either a conventional Pap test alone or an HPV test and a Pap test.

The researchers found abnormal cervical changes in 51 percent more women who had both tests than in the Pap group alone. In subsequent screenings, about 40 percent fewer precancerous lesions were found in the women who'd been screened with both tests compared to women who'd had the Pap test alone, which suggests that overdiagnosis from the HPV test is not as big an issue as some experts had feared.

"Adding HPV testing to Pap testing in routine cervical screening gives a longer protection against the severe precursor lesions of cervical cancer compared to just Pap testing," said study co-author Dr. Joakim Dillner, a professor of virology at Lund University and Malmo University Hospital in Malmo, Sweden.

"In women 30 years of age and older, it is likely to eventually replace the Pap test. The major benefit of the HPV test is that it, compared to Pap testing, enables lengthening the screening interval substantially," Dillner said.

Several questions remain, however. One is how the HPV test compares to the liquid-based Pap test, as neither of these studies used the newer test. And, Saslow pointed out, an emerging group of young women will have been vaccinated against HPV, and it's not clear how that might affect the reliability of the HPV test in the future.

More information

For more on preventing cervical cancer, visit the National Cancer Institute.