Giving drugs to reduce the risk that HIV-positive women pass the infection to their babies is an effective and affordable way to tackle the Aids crisis in sub-Saharan Africa, researchers have calculated.

The researchers have found that even limited use of antiretroviral therapy could have an immediate and substantial impact on the Aids epidemic.

The finding will add to growing international pressure to provide HIV treatment to less developed countries where the virus is running rampant.

A team from the University of British Columbia, Vancouver, Canada, has developed a statistical model to estimate the future impact of antiretroviral use in South Africa from 2000 to 2005.

There are no drugs that can cure Aids but there are a number of treatments that can slow down the growth of the HIV virus.

Drugs can also greatly reduce the risk that a pregnant woman with HIV will pass the virus to her unborn child, either in the womb or through breastfeeding.

First the researchers used their model to estimate the impact HIV was likely to have on the population if no drugs were used.

And then they produced projections of what impact the use of drugs would have.

If no drugs are made available between 2000 and 2005, the investigators estimate that there will be about 2.3 million new Aids cases, 276,000 babies will be born with the HIV virus and average life expectancy will be 46.6 years by 2005.

Big impact

If a quarter of population with HIV received triple-combination treatment it would raise life expectancy by 3.1 years, and prevent more than 430,000 new Aids cases.

However, this would cost US$19billion.

A more affordable strategy would be to give mother with HIV drugs to reduce the risk of transmission to their babies.

The investigators estimate that this could prevent 110,000 HIV-positive births at a cost of just US$54 million.

The analyses were based solely on drug costs, and did not consider the additional infrastructure costs required to finance widespread antiretroviral treatment.

Researcher Evan Wood adds: "Our findings indicate that antiretroviral prophylaxis (to prevent mother-to-child transmission) could have a substantial demographic impact, and support previous works which have demonstrated that it is likely to be cost-effective."

Some of the world's biggest pharmaceuticals firms last month announced dramatic reductions in the price of Aids drugs in the developing world.

The move followed a decision by the US to allow the sale of cheaper, generic drugs to Africa, in a bid to combat the threat of Aids.

The UN estimates more than 11 million people have died of the disease and more than 22 million have HIV which can lead to Aids.