Researchers in the United States and Uganda have identified a cheap and effective drug which could control the spread of Aids.

The drug - named Nevirapine - could prevent up to 400,000 children each year being born with the disease.

The discovery is a ray of hope for health workers involved in the life-or-death battle against Aids - especially in sub-Saharan Africa, where the disease is spreading at an alarming rate.

Every day, 1,800 babies are born in developing countries with HIV - the virus that can result in Aids - passed on by their mothers.

In the hardest-hit parts of sub-Saharan Africa, up to one-third of pregnant women have HIV, and one-third of their children will be born with the virus.

Dr Musoke: A 50% chance the child will not be infected

While other drugs are too expensive, the new drug is said to reduce the chance of Aids being passed from mother to child by up to 50% - and it costs around $4 a dose.

Dr Brookes Jackson, a researcher from Johns Hopkins University in the USA, says the findings are important.

"This is the first regime that will be able to be implemented in a developing country because of its very low cost and its safety," says Dr Jackson, who works in the Ugandan capital, Kampala.

Pallab Ghosh: "Nevirapine is the best hope for many African countries."

According to Professor Catherine Peckham, a specialist in children'd medicine, the major goal is still to prevent HIV infection in women.

But she says that the new drug will have "a profound impact" on HIV infection in children.

Dr Philippa Musoke of Uganda's Makerere University says there is great cultural pressure on women to have children - "a woman is not complete if she does not have children," she says.

Nevirapine: Safe and very cheap

"The option Nevirapine is able to provide is if she does want to have children and she is infected, there's a 50% chance the child will not be - if she takes the drug," Dr Musoke says.

The anti-Aids combination drug, AZT, is more effective if used over a longer period, but costs more than $200 for a short course.