HIV/Aids sufferers from Botswana's neighbours are homing in on its hospitals and clinics in the hope that they might receive free drug treatment to stave off the physical ravages of their illness, medical practitioners in Botswana said on Tuesday.

Botswana is the only southern African country to offer the universal provision of anti-retroviral drugs through its public health system. Most southern African countries have HIV/Aids infection rates above 20 per cent of their economically active population. However, Botswana's neighbours, including South Africa, consider the drugs too expensive and too difficult to administer.

Staff at Francistown's general hospital said patients desperate for the life-prolonging drugs had travelled from Zimbabwe, Tanzania, Namibia and South Africa in the hope of treatment. "They come from all over [the region]. We've had hundreds of Zimbabweans. The sad thing is that in some cases they are being sent to Botswana for treatment," said one medical officer.

Botswana has a strict policy that it will treat only its nationals with anti-retroviral drugs, which it supplies through a partnership with Merck, the US pharmaceutical company, and the Bill and Melinda Gates Foundation. So foreign nationals are turned away from its clinics.

About 2,000 people have so far enrolled for anti-retroviral treatment in the country's four drug dispensing centres. By the end of the year, these numbers are expected to double. However, medical staff in Botswana's largest hospital, the Princess Marina hospital in capital city Gaborone, still fear their facilities may be overwhelmed by HIV/Aids sufferers expecting treatment.

Botswana's 1.7m population has the highest HIV/Aids infection rate in the world. An estimated 38.5 per cent of the sexually active population - those between the ages of 14 and 49 years old - is HIV positive. In Selebi Phikwe, a tin mining town in south-eastern Botswana and the worst affected in the country, more than 60 per cent of adults carry the virus. The death rate from HIV/Aids is not expected to reach a peak for another five to 10 years.

The Gaborone-based African Comprehensive HIV/Aids Partnership (Achap) believes Zimbabwe may have even higher infection rates than Botswana. It fears that the neighbouring country's political and economic crisis, which threatens the mass migration of hungry people over the next four months, is spreading the epidemic.

The Botswana immigration authorities have recorded an increasing number of illegal immigrants travelling from western Zimbabwe - one of the areas worst hit by food shortages - into Botswana in search of food and employment.

President Festus Mogae insists his country does not have the human or financial resources to treat its own small population, let alone that of another country. Studies by local economists and the International Monetary Fund suggest the epidemic will reduce Botswana's economic growth by between one and three percentage points a year over the next 15 years.

"The introduction of anti-retroviral treatment is a major contribution to the fight against HIV/Aids. It offers a window of hope for those with early infections of the virus," said Mr Mogae.

But the window is a narrow one. A census completed by the Central Statistics Office this year showed that Botswana's mortality rate had risen 62 per cent over the past 10 years. The United Nations Joint Programme on HIV/Aids (UNAids) has described the expected toll of HIV/Aids on Botswana's population as heavier than the effects of the world wars in Europe.

For those outside its borders, the prospects for sufferers can only be more bleak.