The scale of the AIDS epidemic in Africa was highlighted this week at the 13th international AIDS conference in Durban, South Africa. In some countries over 20 per cent of adults are now infected with HIV.
The United Nations programme on HIV/AIDS (UNAIDS) figures for the end of 1999 suggest that 34.3m people are living with HIV/AIDS, of whom 5.4m were newly infected in 1999.
The countries most severely affected are in sub-Saharan Africa. In this region alone, there were 4m new HIV infections in 1999. In South Africa, for instance, the proportion of the population infected with HIV has risen from 12.9 per cent to 19.9 per cent in two years.
South Africa has the largest number of cases of HIV/AIDS in the world, with 4.2m infected people. However, neighbouring Botswana has the highest proportion of people infected, with 35.8 per cent of the adult population infected. In Zimbabwe, the likelihood of a 15-year old woman dying before the end of her reproductive years increased from 11 per cent in 1980 to 40 per cent in 1997.
In other areas of the world, UNAIDS data show that rates of HIV infection are lower. In Asia, adult infection rates exceed 1 per cent in only three countries - Cambodia, Myanmar and Thailand. However, because of the large populations in Asia, even low prevalence rates translate into large numbers of infections. In India, 3.7m people are infected with HIV, second only to South Africa, despite a much smaller prevalence of 0.7 per cent. Figures for other countries are illustrated in Figure 1.
Figure 1: Estimates of percentage of adults with HIV infection at the end of 1999 Source: UNAIDS |
The effect of HIV in developing countries is so severe that it is affecting the population structure, UNAIDS says.
The population structure for developing countries is generally described as a pyramid - a wide base because of high birth rates that narrows with increasing age caused by high death rates. Countries with lower birth and death rates (because of improved health) have a column-shaped population structure. However, AIDS is causing the production of a completely new shape called a "population chimney" (see Figure 2). The most obvious structural change is a radical shrink in the population aged between 20 and 40. There is also a reduction in number of children because of the increased death rate of women of reproductive age and because of transmission of HIV from mother to infant.
The United States Census Bureau says that in Botswana in 20 years time there will be more adults in their 60s and 70s than adults in their 40s and 50s. UNAIDS speculates that the premature death of half the adult population will have a radical effect on virtually every aspect of social and economic life. In terms of implications for society, it will mean that a small number of young adults will have to support large numbers of young and elderly people.
Figure 2: Projected population structure in Botswana, 2020, with (black bars) and without (grey bars) the AIDS epidemic Source: UNAIDS |
A phase I clinical trial of an AIDS vaccine which is being developed in the UK is expected to start soon.
The vaccine is being developed by Professor Andrew McMichael, from the Medical Research Council human immunology department at Oxford, in collaboration with researchers in Nairobi. Final ethical approval is still awaited but, if granted, the UK trial should start by the end of the summer. The phase I trial will involve volunteers (aged 18 to 60) at low risk of HIV infection.
The vaccine being developed uses DNA from the strain of HIV that is prevalent in Kenya. It contains a section of viral DNA designed to stimulate an immune response, inserted into a modified vaccinia virus. Once the outcome of the Oxford trial is known, around the end of 2000, a similar study will be initiated in Nairobi. If this trial is successful, researchers will be able to start phase II trials in volunteers at high risk of infection to see if the vaccine offers protection.
A study presented at the Durban conference found that women have lower levels of HIV in their blood than men, especially during early phases of infection, but have the same risk as men of developing AIDS. Professor Timothy Sterling (Johns Hopkins university, US) studied levels of HIV infection in 156 men and 46 women. Men who progressed to AIDS had an average viral load of 78,000 copies per ml in the first year, while women who progressed to AIDS had a viral load of 17,00 copies per ml. The differences continued until the fourth year. Patients are generally offered antiretroviral treatment when their viral loads are over 20,000, Dr Sterling pointed out. He concluded: "Current cut offs would result in sex-biased differences in treatment eligibility."