Three different human retroviruses, HIV-1, HIV-2 and HTLV-I, are circulating in the general population in Guinea-Bissau. Previous community studies in the country have suggested that women older than 45 years of age are more susceptible to HIV-2-infections. The aim of the present thesis was to further analyse epidemiological patterns of the three different retroviruses with regard to age and gender, and to relate them to behavioural and socio-economic factors that may explain the distribution of the various retroviruses. The age and gender patterns are also compared with populations in other parts of sub-Saharan Africa
A literature review study was performed of population-based studies from various parts of sub-Saharan Africa. All community studies of HIV-1, HIV-2 and HTLV-I between 1987-1997 were identified through a MedLine search in order to compare prevalence and incidence rates between men and women of young and old age groups.
Field studies were conducted in two different areas in Guinea-Bissau. Three studies were performed in a rural area, Caio. Samples from an HIV survey conducted in the area during 1989-1991, encompassing all adults aged 15 years and over, were tested for HTLV-I, and age and sex pattern, and risk factor analyses for HTLV-I were performed. In addition, an analysis of all HTLV-I infected individuals and their spouses was performed to assess risk factors for HTLV-I transmission within married couples.
A sub-sample of all HIV negative and HIV-2-positive women identified in an HIV survey performed in Caio during 1997-1998, including adults >15 years of age, were selected for inclusion in an analysis comparing socio-economic and behavioural aspects of women of different age group. The age variable was adjusted for various socio-economic and behavioural factors.
In a semi-urban area, Bissau, a follow-up study was performed of two cohorts of individuals aged 35 years and over. Questionnaires were administered covering a variety of potential risk factors, and blood sample was drawn and tested for HIV-1, HIV-2 and HTLV-I. Prevalence, incidence and mortality patterns were analysed according to age and gender.
Results and Discussion
Comparing age groups >45/50 years of age with young age groups, we found generally increased F/M prevalence ratios for all three retroviruses, HIV-1, HIV-2 and HTLV-I, in different parts of sub-Saharan Africa. One incidence study was included, giving a similar increased F/M incidence ratio, comparing old with young age groups.
In Guinea-Bissau we found a similar pattern of increased F/M prevalence ratios in older age groups, both in the rural and the semi-urban area. Generally, the prevalence of retrovirus infections was higher in women than in men. In Bissau, the overall HIV-1 prevalence was 2.1%, for HIV-2 13.5% and for HTLV-I 7.1%. In Caio, the overall HTLV-I prevalence was 5.2%. There was a high degree of clustering of HTLV-I, that was ascribed to families and the transmission within married couples. Duration of marriage and HIV-2 infection in the wife were risk factors for HTLV-I in spouses of HTLV-I infected men. We were not able to identify any risk factors for HTLV-I in husbands of HTLV-I infected women.
Further analyses revealed that various combinations of dual infections with HIV-1, HIV-2 and HTLV-I were more common in women than in men, both in the semi-urban area and the rural area. In addition, the prevalence of dual infections increased with age in women, whereas this pattern was not observed in men. Adjusting for various behavioural variables did not modify this pattern of increased prevalence of retrovirus infections in older women. Finally, we did not find any differences in retroviral associated mortality between men and women.
We have found that various types and combinations of retroviral infections are more common in older women than in men. We have additionally found that differences in behaviour between young and old women do not explain this increased prevalence, and that there are no apparent differences in retrovirus associated mortality between men and women that could explain the pattern. Hence, biological factors should be considered such as an increased susceptibility to another retrovirus infection when already infected with one retrovirus, or an increased susceptibility due to hormonal changes in menopausal or pre-menopausal women. Further research is needed to clarify this, and if it is shown that such biological mechanisms are implicated, this could constitute a target of relatively simple preventive measures. Finally, considering that current politics aim at making HIV drugs available also to the African continent, HIV infected individuals will survive longer, and we may face an increasing prevalence of HIV among older women.