Doctors are finding new uses for HIV drugs, with one study showing they might safely protect women at high risk of infection and a second showing that people can safely skip the most toxic pills.

Research to be presented at the 16th International Conference on AIDS, which opens on Sunday, shows new benefits from drugs that help suppress the fatal and incurable virus.

The human immunodeficiency virus that causes AIDS infects close to 39 million people globally. Since the virus started spreading globally in the 1980s it has killed 25 million people and orphaned millions more.

There is no vaccine and no cure. Only condoms and complete sexual abstinence have been shown to prevent infection.

Family Health International tested an experimental approach called pre-exposure prophylaxis or PrEP using a drug called tenofovir. Researchers believe the drug, made by the California-based Gilead Sciences Inc. under the brand name Viread, could keep healthy people from getting HIV.

The researchers gave either the pill or a placebo to 936 high-risk women in Cameroon, Ghana and Nigeria.

They were not able to tell if the pills actually prevented infection with the AIDS virus but tested the women's kidney and liver function to make sure taking the drugs was safe. They also wanted to see if the women would take the drugs consistently.

"The encouraging news was in regard to safety, acceptability

and risk," Ward Cates, who helped lead the study, said in a telephone interview.

One worry was that the women would feel protected by the drug and would fail to use condoms, or have sex more often. But this did not happen during the trial, Cate said.

The women, all recruited because they were sex workers, or had sex frequently with different men, all got counseling and condoms at every visit.

Several women got pregnant -- at a rate of about 40 per 100 women per year -- suggesting that the women did not always use condoms, Cate noted.

"In general, access to condoms is limited in many of these resource-poor settings," Cates said.

"This approach is not intended for people who are in the general population but only for people in very high-risk settings for whom no other HIV prevention approach is available."

SAFER COMBINATIONS

In some countries, HIV drug cocktails can keep patients healthy. There are more than 20 drugs available now and it is not always clear which combination is best. Some drugs cause more side-effects than others.

A team led by Dr. Sharon Riddler of the University of Pittsburgh School of Medicine at the University of Pittsburgh tested some of the combinations to see if patients could skip the oldest class of HIV medications, called nucleoside reverse transcriptase inhibitors, also known as NRTIs or "nukes."

They can cause intolerable side effects in some patients, ranging from diarrhea to hepatitis.

Their test of 753 volunteers at 55 centers showed that using two drugs in the NRTI class with a drug called efavirenz, a non-nucleoside reverse transcriptase inhibitor, suppressed the virus in more people than a more widely used combination.

"Now that we've completed the trial, there should be little doubt that patients can benefit from this 'nuke'-sparing treatment regimen when NRTI side effects are a problem," Ridley said in a statement.

An experimental HIV drug in a new class called integrase inhibitors helps control the virus well combined with other drugs commonly used in AIDS cocktails, its maker Merck and Co. reported on Saturday.

The findings, to be presented at an international AIDS meeting, offer a potential new weapon in the growing armory of drugs that fight HIV. The drug mixtures can keep HIV patients healthy for years, although they are not a cure.

Merck said the drug, known by its experimental name MK-0518, worked as well as older drugs to suppress the AIDS virus when combined with Gilead Sciences' tenofovir, known commercially as Viread and GlaxoSmithkline's lamivudine, sold under the brand name Epivir.

They compared the new drug with a similar cocktail using Bristol Myer Squibb's efavirenz, sold under the brand names Sustiva and Stocrin. For the study, 198 HIV-infected patients took one or the other mixture for 24 weeks.

Both combinations lower viral load -- the amount of the virus be found in blood. Suppressing the virus limits the damage it can do to a patient's immune system.

"This early study showed a rapid and significant reduction in viral load up to 24 weeks with MK-0518," Dr. Martin Markowitz of the Aaron Diamond AIDS Research Center in New York, who led the study, said in a statement.

"This study should lend further insight into the potential of HIV integrase inhibitors as a new and exciting class of antiretroviral agents."

There are several classes of HIV drugs, also known as antiretroviral drugs. Each class attacks the virus at a different point in its cycle of replication.

Combining the drugs in a cocktail suppresses the virus even more, but eventually the virus in a patient's body escapes the effects of drugs so new approaches and combinations are needed to control it.

When the human immunodeficiency virus infects a cell, usually an immune system cell called a T-cell, it attaches to the cell, pierces it and inserts its own genetic material.

The viral DNA re-programs the cell, in essence hijacking it, and forces it to produce copy after copy of the virus, which it pumps into the blood to infect other cells.

The integrase inhibitors stop the insertion of the HIV viral DNA into human DNA, shutting down the virus factory.

Other HIV drugs target other enzymes involved in this hijacking process.

Several companies are working on integrase inhibitors but none is approved yet.

Only one in five people with HIV in poor and middle-income countries receives the drugs that treat the virus, said a report by the U.S. Centers for Disease Control and Prevention on Thursday.

That is despite a 200 percent rise in the number of people receiving the drug treatment between 2003 and 2005 as individual countries worked to meet a target of treating 3 million people with the drugs by 2005, the government agency's report said.

The dramatic increase in the number of people receiving the drugs means that globally there will be a rise in people living with HIV and thus a growing need to boost measures against HIV transmission, said the report.

In all, 4.1 million people were newly infected with HIV and 38.6 million were living with HIV and AIDS in 2005 in an epidemic focused on sub-Saharan Africa.

"Approximately 10 percent of the world population lives in sub-Saharan Africa but the region is home to approximately 64 percent of the world population living with HIV ... More women are HIV-infected than men," said the report.

Some African countries including Kenya, Uganda and Zimbabwe have seen a decline in adult HIV prevalence but in southern Africa, the epicenter of the pandemic, only 17 percent of those infected with the virus received the drug treatment.

The drugs save lives by treating infections caused by retroviruses, including HIV.

The report was published ahead of the 16th International AIDS conference in Toronto, Canada, which starts August 13.

There has been major progress in the drive to prevent HIV-positive mothers passing the virus on to their children but only 8 percent of the relevant women receive services such as health education, the report said.

Researchers in a separate study by the CDC and the Thailand Ministry of Health found an "alarming" 64 percent increase in sex between men in Bangkok between 2003 and 2005 and "low awareness" of HIV status among all men in the study."

"The study ... underscores the need to reach (the group) with more effective behavioral and biomedical interventions, more frequent and increased access to HIV counseling and testing, improved STD diagnosis and treatment and community awareness and support," said the report.

The AIDS virus has an accomplice that helps it infect the immune system cells it attacks -- other immune system cells, U.S. researchers reported on Saturday.

In fact, these other cells, known as B cells, may be key to infection, the University of Pittsburgh researchers told an international AIDS conference. "The research supports a new role for B cells in the development and spread of HIV between cells," said Dr. Charles Rinaldo, who led the study.

The findings may help find a way to block infection, and help explain why the virus can hide out in "reservoirs" inside the body for decades.

The AIDS virus is especially hard to fight because it infects the immune system. It favors cells called CD4 T-cells.

It gets into the cells using two molecular doorways, called receptors. They are CD4 and either CCR5 or CXCR4 and are found only on T-cells.

Other immune cells were thought to be uninvolved. But Rinaldo's team found that other immune cells called B cells make a protein called DC-SIGN that seems necessary for HIV to ever infect a cell.

The researchers looked at B cells from 33 healthy subjects and 20 adult patients with HIV. About 8 percent of these cells expressed, or made, DC-SIGN.

One study showed that B cells harbored viruses that could be transmitted to T cells for as long as two days. HIV had little effect on the T cells when B cells were not around.

The researchers found a compound that blocks DC-SIGN.

When they blocked DC-SIGN in B cells, and put them in with T-cells in a lab dish, the virus was unable to infect the T-cells, the researchers said in a statement to be presented more fully at the 16th International Conference on AIDS being held in Toronto.

There is no cure for the AIDS virus, which infects about 40 million people globally and has killed 25 million since it was first noted in the early 1980s. There is also no vaccine.

Drugs can help control it but the virus cannot be eradicated from the body. Understanding how it infects cells may help scientists discover how to clear it from the body or prevent infection in the first place.

Fewer U.S. high school students are having sex, and the ones who do are less likely to have multiple partners, according to a report issued on Thursday by the Centers for Disease Control and Prevention.

Some 46.8 percent of students said they engaged in sexual intercourse in a 2005 survey, down from 54.1 percent in 1991, according to the report.

Some 14.3 percent of students in 2005 said they have had multiple partners, defined as sex with four different people during one's lifetime. That figure is down from 18.7 percent in 1991.

At the same time, the number of students who say they used a condom the last time they had intercourse rose to 62.8 percent in 2005 from 46.2 percent in 1991, the survey said.

The report was based on student responses to anonymous, self-administered questionnaires in public and private schools in all 50 states and the District of Columbia by the CDC's Youth Risk Behavior Surveys.

One aim was to determine the extent to which U.S. students were at risk from HIV or other behavior-related illnesses. High school students are generally aged 15 to 18.

Some 2.1 percent of students said they had injected illegal drugs at least once, the same as in 1995, the survey said.

"During 1995-2005, the percentage of U.S. high school students who ever injected drugs remained less than 4 percent. However, many students still engage in HIV-related risk behaviors," the report said.

The report was published ahead of the 16th International AIDS conference, billed as the world's largest, which starts August 13 in Toronto, Canada.

Can the drugs that keep HIV-positive people alive also make it safer to enjoy carefree sex -- much as during the pre-AIDS 1970s?

Health officials in the United States, Thailand, Botswana and elsewhere are now trying to find out by conducting trials in which healthy people take drug cocktails that suppress the virus.

"The information that we have indicates that this is a very promising approach," said the University of California, San Francisco's Robert Grant, who is overseeing an upcoming study to be conducted in Peru.

"The use of anti-viral drugs for prevention has been evaluated in animal models, especially non-human primates. They have shown to be highly effective in preventing acquisition of viruses that are similar to HIV."

Researchers have already completed one study in Ghana on the subject, known as Pre-Exposure Prophylaxis (or PrEP), and will present the first findings on the topic next week at the International AIDS conference in Toronto.

To date, the only proven way to prevent AIDS is abstinence or condom use. Yet in recent years researchers have noted a potentially dangerous increase in unprotected sex, including among American gays. Some theorize that the availability of AIDS drugs has made people complacent.

If PrEP works -- and it will likely take several years to gain a conclusive answer -- "it could stand to save thousands of people from being infected," said Melanie Thompson, who is leading a PrEP study in Atlanta.

The studies have generated some controversy. Two years ago Cambodia halted a PrEP study, and the African nations of Cameroon and Nigeria pulled out of trials after local protest.

COMPLICATED ISSUE

Since the diagnosis of AIDS a quarter century ago, overcoming its risk, for example, by devising a vaccine has proved elusive. The United Nations says 25 million have died since the epidemic emerged.

Yet antiretroviral drugs have kept people with the HIV virus that causes AIDS alive, giving hopes that drugs such as tenofovir (Viread) or the two-drug combination pill Truvada made by the California-based biotech company Gilead Sciences could keep the healthy from getting HIV.

"I would hope that ultimately there is a vaccine. I must say that a preventive vaccine I don't expect to see in my lifetime," said Thomas Coates, an expert on HIV prevention at the University of California, Los Angeles. "In the meantime we do need other prevention strategies."

Even if the approach is shown to work, it may prove very costly. A month's supply of Truvada at U.S. wholesale prices costs $735.36, Gilead says, although the medication is offered at far lower prices in developing countries.

"The population that might benefit from this is huge," said Howard Jaffe, the president of the Gilead Foundation.

Yet he said the company would not market the drug as a prophylactic, out of concern about liability, and because insurance companies are unlikely to fund such a use. "It's likely to be a very charged and complicated issue," he said.

STRONG NEED IN SAN FRANCISCO

Scientists are studying whether the pills work as an HIV prophylactic and whether they pose any risk to the healthy.

"The concern is, of course, you're giving potentially toxic medications to people who are otherwise healthy," said Coates. "I think we have probably a reasonable assurance that the drugs are safe. In terms of effectiveness...that is the million- dollar question."

Famous for its active gay community, San Francisco earlier this year launched a study on the potential side effects of the medication for the healthy as well as any effects on behavior.

"We urgently need new ways to prevent HIV infection," said Albert Liu, the study's director.

Anecdotal evidence suggests at least a small number of healthy gay men already take the drugs, hoping for protection before sex -- a practice doctors do not endorse.

San Francisco experiences 15-20 new infections a week, and city officials say that just more than a quarter of the city's estimated 63,577 gay men aged 15 and above are HIV positive.

The study, sponsored by the Centers for Disease Control and Prevention, aimed to have 400 participants in San Francisco and Atlanta, but has struggled to find volunteers. More than 200 are now enrolled.

Medical experts say if the PrEP tests prove effective, those at risk, from prostitutes and drug addicts to those living a sexually risky lifestyle, could take the pills for months or years of their lives. It's unclear whether funds would be forthcoming to pay for their treatment or if they would adhere to the drug regimen.

Still, medical experts caution that the pills will unlikely prove a free pass to promiscuity.

"We would never recommend that it be used as an excuse or a reason to have unprotected sex," Liu said. "This approach may not be 100 percent effective .... We would offer it in addition to proven prevention strategies such as, you know, condoms, risk reductions counseling, getting tested frequently."

More people are getting tuberculosis because of AIDS and more die of AIDS because of TB, yet doctors fail to recognize the respiratory disease in AIDS patients and governments do little about it, according to a report released on Tuesday.

Sexier topics like avian flu get immediate attention while 2 million people die every year of tuberculosis, and 9 million become infected, according to the report from the Open Society Institute, a foundation set up by financier George Soros.

Together, TB and AIDS are causing a "double plague," Stephen Lewis, the United Nations Special Envoy for AIDS in Africa told reporters in a telephone briefing.

"Governments and the international community have got to realize they have on their hands two simultaneous and interrelated catastrophes," Lewis said.

"We must confront both together. We need more resources. We need diagnostics. We need better drugs."

Lewis and staffers who wrote the report said they hope to use the 16th International AIDS Conference in Toronto, which opens on Sunday, to build interest in the issue.

When people become infected with TB and AIDS it is almost "always an irreversible formula, cause for death," Lewis said.

"TB is in fact the most common cause of death for people living with AIDS," he added. "Ninety-nine percent of those infections and deaths are in the developing world."

TB can be cured with several months of treatment with antibiotics.

LIVING EXAMPLE

Ezio Santos Filho, a lawyer and AIDS and TB activist in Brazil, said he is a living example of the problem.

He has been infected with the AIDS virus since 1985 and became infected with tuberculosis in 1992 when working with Brazilian TB patients.

"When people have AIDS it is difficult to diagnose TB," Filho said.

"Normally they don't have all the symptoms, all the typical characteristics that people without AIDS would have. People cough less and people have less sputum when they have AIDS."

In addition, the report said, only a third of all TB smear tests in HIV-positive patients give an accurate positive result.

"You could do it with a chest x-ray but obviously that kind of technology is not readily available to the developing world," Lewis said.

Filho said even though Brazil has good public health care and he has private health insurance, it took him 40 days to be diagnosed.

"So this is a typical problem why TB kills so many people with HIV. Because they don't get diagnosed in time," he said.

"Also, I know all the physicians who deal with TB in the country, all the key people and still the diagnosis took so long to be done," Filho said.

The report said in Tanzania, for example, only 47 percent of TB cases are detected. Undiagnosed patients spread TB.

"And for people living with HIV/AIDS, even a short delay in accessing TB treatment can be fatal," the report said. HIV destroys the immune system. Drug cocktails can help control this but there is no cure and the drugs are usually not available in poorer countries.

Olayide Akanni of Journalists Against AIDS in Nigeria, who worked on the report, said activists, public health authorities and other experts have all failed to address the issue.

"There is no coordination between TB and HIV programs," she said. "In most programs, TB programs go underfunded and neglected."

And there is little interest, said Afsan Chowdhury of the Bangladesh Rural Advancement Committee.

"There is no interest because it is a disease of the poor," Chowdhury said. "On the other hand bird flu is quite a dramatic disease."