The findings support those who argue that antiretrovirals -- which treat the human immunodeficiency virus (HIV) but do not eliminate it completely -- are also a potent weapon for preventing viral spread.

The paper looked at the population of the Canadian province of British Columbia, examining coverage of antiretroviral treatment and new cases of infection between 1996 and 2009.

Over this period, the annual tally of new cases fell by 52 percent, the researchers found.

For every 100 patients that were placed on the drugs, new diagnoses of HIV fell by three percent.

The paper, published in The Lancet, is authored by Julio Montaner, director of the British Columbia Centre for Excellence in HIV/AIDS in Vancouver, and president of the International AIDS Society.

The time scale of the study dates back to the introduction in 1996 of the triple HIV drug cocktail, which now provides a lifeline for five million badly-infected people.

During the period under study, the number of people on this combination therapy rose from 837 to 5,413 but the number of new HIV diagnoses fell from 702 to 338 per year.

Concentrations of virus in the blood among treated patients also fell sharply.

Antiretrovirals can reduce levels of HIV to below detectable levels. The virus retreats to "reservoirs" such as the lymph glands, where so far no way has been found to eliminate it -- and if the drugs are stopped, it rebounds.

But having very low levels of virus also logically implies a fall in the risk of handing on the pathogen to others.

Previous studies have also highlighted the indirect benefit of antiretrovirals in preventing new cases of HIV.

As a result, some specialists say the time is near to declare antiretrovirals a preventative tool, alongside the condom, that should be added to the panoply of options for preventing spread of HIV.

Such calls have met with concern or even anger. Critics say HIV-infected people may be tempted to dispense with safe-sex measures, thus exposing partners to a risk, even very small, of infection.

The new study cautiously backs a policy review.

"Our results... provide a strong rationale for re-examination of the HIV prevention and treatment dichotomy," it says.

"Furthermore, our results should serve to re-energise the G8's universal access [to treatment] pledge as a means to curb the effect of AIDS and the growth of the HIV pandemic."

The six-day International AIDS Conference was to open in Vienna late Sunday, drawing an expected attendance of more than 20,000 scientists, policymakers and grassroots workers.

More than 33 million people have AIDS or HIV, according to estimates for the end of 2008. At least 25 million have died of acquired immune deficiency syndrome (AIDS) since the disease first came to light in 1981.

earlier related report
HIV: Start treatment earlier, says panel
Vienna (AFP) July 18, 2010 - A major expert panel recommended ahead of the start of the world AIDS conference here Sunday that patients with HIV start antiretroviral drugs at an earlier stage of infection.

Earlier initiation of the famous combination of drugs that repress the human immunodeficiency virus (HIV) can reduce long-term mortality and sickness, the group said.

It set out its recommendations in a paper published by the Journal of the American Medical Association (JAMA) and presented in Vienna just before the six-day 18th International AIDS Conference got underway.

The group suggested that infected individuals be treated when their count of CD4 cells -- the key immune cells targeted by HIV -- reaches a threshold of 500 CD4 cells per microlitre of blood or below.

Therapy "should be considered" for non-symptomatic patients with more than 500 cells per microlitre, it said, adding: "There is no CD4 cell count threshold at which initiating therapy is contra-indicated," or inadvisable.

Therapy is also recommended for patients who are pregnant, older than 60, are co-infected by hepatitis B or C and at high risk for cardiovascular disease.

The CD4 count is the one of major barometers of infection by HIV.

A healthy, uninfected person has a CD4 count of between 1,000 and 1,500 cells per microlitre. Under UN guidelines, treatment is advised when infection is somewhat more severe, at 350 CD4 cells per microlitre.

Changes in guidelines have consequences that reach into many spheres.

Treating people sooner than before means boosting the drugs bill at a time of widening austerity.

It also requires having the infrastructure in place -- doctors, nurses and labs -- to ensure the therapy is being properly followed and the patient is responding to treatment.

In practical terms, the guidelines will be most relevant in rich countries with the drug budgets and medical infrastructure to treat people earlier, the authors said.

"We tried to stick with the data that were available and to make the best scientific recommendations... (but) they are intended for more highly-resourced countries," said lead investigator Melanie Thompson of the AIDS Research Consortium of Atlanta and chairwoman of the US branch of the International AIDS Society (IAS).

The panel looked at the latest investigations into the benefits of earlier treatment, weighed against the risks of side effects from antiretrovirals, a powerful drug that has to be taken daily for the rest of a patient's life.

These probes showed that HIV, by replicating unchallenged in the blood, had long-term implications for sickness and the death rate.

In addition, new antiretrovirals have come to the fore that have fewer side effects and are well-suited for initiating therapy, the paper said.

International guidelines set down in 2006 by the UN's World Health Organisation (WHO) advised doctors to begin therapy when the patient's count of CD4 cells reaches 200 cells or less per microlitre of blood.

This figure was raised by the WHO last year to 350 CD4 cells per microlitre of blood.

Thompson said the WHO recommendations were not a factor in the panel's debate. She also wondered whether the WHO had to factor in the need to offer advice that understood the reality in cash-strapped countries with high prevalence of HIV.

Antiretrovirals can reduce levels of HIV to below detectable levels, but cannot eradicate the pathogen completely. The microbe holes up in a small number of cells and leaps out again if the drugs are stopped.

More than 33 million people have AIDS or HIV, according to UN estimates for the end of 2008. At least 25 million have died of acquired immune deficiency syndrome (AIDS) since the disease first came to light in 1981.

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