Vertical Transmission of HIV may occur in Utero, as infection acquired at birth (peripartum or through breastfeeding. The provision of short-course zidovudine or single dose nevaripine have each been shown to reduce a substantial proportion of infant infection, however, more than 10 percent of infants in Africa are still infection within 1-2 months and 10-15 percent acquire infection while breast-feeding. In the Southern Cone of Africa, HIV infection is almost exclusively caused by subtype C HIV, which currently accounts for the majority of HIV infection globally. Viral factors in subtype C infection, maternal and infant virus load, conserved T cell epitopes, the chemokine receptor tropism and envelope diversity of HIV are characteristics associated with transmission. Host factors in mothers and infants, humoral immune responses, shared HLA alleles and specific HLA types also effect transmission and progression of infection. While short-course therapies can reduce vertical transmission, mutation, selection and dissemination of drug resistant virus may reduce the efficacy of peripartum interventions and potential therapies. In studies in Zimbabwe 363 HIV seropositive pregnant women will receive peripartum treatment with either zidovudine (200) or single dose nevirapine (163). However the rate of transmission is still estimated to exceed 15 percent. Through careful collection of samples from women and their infants, viral and host risk factors will be characterized in the transmission of subtype C viruses in Southern Africa, in the setting of short-course antiretroviral therapy. As subtype C infection is rapidly dominating the HIV pandemic in Africa and India, and understanding of the features of this subtype is critical to both drug and vaccine interventions. Long-term, community-based follow-up of mothers and infants will define the interactions between drug treatments, viral and host factors and clinical outcomes including infection and disease. The goal is to develop better interventions for subtype C HIV infected women and their infants in Southern Africa and to describe the range of viruses transmitted in Southern African setting. Genotypic information about women and their infants who become infected, and those who escape infection despite exposure to maternal virus, will help to define the optimal antigens and epitopes that should be included in prophylactic vaccines for subtype C HIV in Africa.
