The emergence of HIV/AIDS in Africa

The recent spread of HIV/AIDS in Africa must be seen in the broader context of emerging infectious diseases, whose epidemiology results from changes in the equilibrium between the agent, the host, and the environment. For sexually transmitted agents such as HIV, epidemic spread requires a high basic reproductive rate (number of secondary cases generated by one primary case), which is itself dependent on the rate of change of sex partners, the transmissibility of the agent, and the duration of infectiousness. Factors relating to the agent which may have influenced the spread of HIV in Africa are viral types (HIV-1, HIV-2) and subtypes, of which at least 9 exist for the main group of HIV-1. Major host factors include sexual behaviour and sexual networks, commercial sex, sexually transmitted diseases, condom use, and circumcision status in males. Most difficult to study are environmental factors in the broadest sense, such as behavioral norms, poverty, migration, and HIV/AIDS prevention efforts. Any model attempting to explain HIV/AIDS emergence must account for the extreme heterogeneity of the epidemic within the African continent, and must be relevant to the application of more effective interventions. Although descriptive and analytic epidemiology remain necessary, intervention-oriented research on HIV/AIDS is now the priority in Africa.