HIV-1 infection in Tanzania with special reference to early diagnosis in children and preparations for vaccine trials

Abstract: The studies reported in this thesis aimed at identifying simple, suitable and affordable assays for HIV monitoring and for early diagnosis in children, and establishing the suitability of a potential cohort for HIV vaccine trials in Tanzania. In a field evaluation of three alternative methods for quantification of T-lymphocyte subsets, we found high overall correlation coefficients (r>0.9) of FACScount and Dynabeads CD4+ and CD8+ T-lymphocyte counts with those of flow cytometry. A lower correlation (r=0.631) was obtained for TRAx CD4 ELISA counts. Therefore, FACScount and Dynabeads methods provide alternatives to flow cytometry for the enumeration of T-lymphocyte subsets in laboratories with limited facilities. A modified heat-denatured p24 antigen assay, which is simpler and cheaper than HIV DNA PCR tests, was shown to have a high sensitivity (98.7%, 123/125) for early diagnosis of HIV-1 infection in infants. We also showed that p24 antigenemia was highly predictive of mother -to - child transmission of HIV-1. We utilized the assay to confirm the HIV-1 infection status of children below 18 months of age in a study among children (aged 1month-8yrs) hospitalized at Muhimbili Medical Centre. The overall prevalence of HIV-1 infection among the 2015 children included in the study was 19.2%. We compared the performance of several in-house nested PCR systems to that of the Amplicor (Roche) HIV-1 PCR kit in the detection of HIV-1 DNA in Tanzanian blood samples prepared by the ficoll-isopaque (FIP) centrifugation and the Amplicor PCR sample preparation methods. Samples prepared by the Amplicor method were found to be more suitable for PCR than those prepared by the FIP method. A sensitivity of 100% was achieved by combining two in-house primer sets. The sensitivity of the standard Amplicor HIV-1 PCR kit was 59%, whereas that of a modified Amplicor HIV-1 PCR test was 98%. We further compared the performance of a prototype Roche Amplicor version 1.5 PCR test with that of the standard Amplicor PCR test for the detection of HIV-1 DNA in blood samples from asymptomatic HIV-seropositive Tanzanians. The sensitivities of the Amplicor 1.5 PCR and the standard PCR assays were 99.1% (105/106) and 97% (99/102) respectively. Specificity was 100% for both assays. HIV-1 subtyping by heteroduplex mobility assay of 101 samples showed that 47% were subtype A, 30% subtype C, 20% subtype D and 3% were indeterminate. In the standard assay, a statistically significantly higher proportion of subtype A samples had a low level of reactivity compared with the subtypes C and D samples while in the prototype assay all three subtypes showed a high level of reactivity. Therefore, the Amplicor version 1.5 PCR is suitable for the detection of HIV-1 DNA in samples from geographic areas where HIV-1 subtypes A, C and D are prevalent. As part of preparations for possible future HIV vaccine trials in Tanzania, we determined the prevalence and incidence of HIV-1 infection, active syphilis and their associated factors in a cohort of police officers in Dar es Salaam. The overall HIV-1 seroprevalence at recruitment was 13.8% (378/2733). The overall HIV-1 incidence was 19.9/1000 person years at risk (PYAR); 19.6/1000 PYAR for males and 22.4/1000 PYAR for females. The overall prevalence and incidence of active syphilis were 3.1% (88/2850) and 8.6/100 (26/3149) person years, respectively. There was high risk sexual practice among the police officers, especially males. From these findings, the police officers cohort was considered to be a suitable population group for HIV vaccine trials.