An expected decline in South Africa's population because of its rampaging AIDS epidemic will dramatically affect the country's role as investor and peacekeeper, it says.

"Countries should begin planning how they will cope with decreased South African aid and investment, should such a scenario materialise because of AIDS," says the piece, authored by Jerome Singh of the Centre for the AIDS Programme of Research in South Africa (CAPRISA).

"The effect of AIDS on South Africa also threatens to destabilise security in parts of Africa, and possibly elsewhere too."

Singh's argument is based on the latest UN figures, which say around 5.3 million people in South Africa have HIV or AIDS, the highest of any country in the world.

The UN Population Fund (UNPF) says South Africa's current population of 45 million is likely to shrink to 40 million by 2050 because of AIDS mortality. Previous estimates for 2050 projected a population twice as big.

Singh says this is bound to have a traumatic effect on South Africa's economy.

He predicts that the South African government and corporations would be prompted to scale back foreign investment, which has surged since the country's first multiracial elections in 1994. A pullback would increase poverty and unemployment in other countries.

Another question is whether South Africa will be able to sustain its leading role as continental peacekeeper, he says.

"The relative peace currently prevailing in conflict-riddled countries, such as Liberia, Burundi and the Democratic Republic of Congo has been attributed, in part, to the presence of about 2,800 South African peacekeepers in these and other African hotspots."

Says Singh: "The effect of AIDS-related natural attrition, combined with a rise in rates of infection with HIV among South African troops in the years ahead, can be expected to reduce the number of South African troops eligible for peacekeeping missions in troubled African regions.

"The downscaling could threaten peace and stability in regions where South African troops currently serve, or could be called on to serve in."

Singh is also an academic at the Howard College School of Law at the University of KwaZulu-Natal in Durban and at the University of Toronto, Canada.

The Lancet, published in London, ran the commentary in an issue devoted to AIDS ahead of next Wednesday's World AIDS Day.

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