The HIV-1 epidemic: low- to middle-income countries

Low- to middle-income countries bear the overwhelming burden of the human immunode-ficiency virus type 1 (HIV-1) epidemic in terms of the numbers of their citizens living with HIV/AIDS (acquired immunodeficiency syndrome), the high degrees of viral diversity often involving multiple HIV-1 clades circulating within their populations, and the social and economic factors that compromise current control measures. Distinct epidemics have emerged in different geographical areas. These epidemics differ in their severity, the popu-lation groups they affect, their associated risk behaviors, and the viral strains that drive them. In addition to inflicting great human cost, the high burden of HIV infection has a major impact on the social and economic development of many low- to middle-income countries. Furthermore, the high degrees of viral diversity associated with multiclade HIV epidemics impacts viral diagnosis and pathogenicity and treatment and poses daunting chal-lenges for effective vaccine development. Although the first cases of acquired immuno-deficiency syndrome (AIDS)were identified in North America in 1981, molecular epidemi-ology studies have placed the geographical ori