Evolution of human immunodeficiency virus type 1 serotypes in northern Tanzania: a retrospective study.

The HIV-1 epidemic in Tanzania is characterized by the circulation of heterogeneous virus subtypes. A retrospective study was conducted to determine the changing pattern of circulating HIV-1 subtypes in northern Tanzania. A peptide-binding enzyme immunoassay (PEIA) was employed to analyse 305 HIV-1 positive serum and plasma samples collected between 1985 and 2005. Samples were serotyped using synthetic peptides representing HIV-1 genotypes A-E derived from consensus gp120 V3 sequences. Plasma samples collected in 2005 were V3 genotyped for comparison with PEIA results. In 1985, serotypes A and D were co-circulating while serotype C was first detected in 1990. In 2001 and 2005, serotype C was the most prevalent, serotype A was stable, and serotype D was declining. PEIA is relatively rapid and simple to perform compared to molecular approaches, and is a valuable epidemiological tool in regions with limited resources. HIV-1 classification into serotypes based on antigenic V3 diversity may be a useful screening tool for the identification of HIV-1 variants with regard to diagnosis, treatment, disease progression and candidate vaccine development.

Mosquito abundance, bed net coverage and other factors associated with variations in sporozoite infectivity rates in four villages of rural Tanzania.

BACKGROUND: Entomological surveys are of great importance in decision-making processes regarding malaria control strategies because they help to identify associations between vector abundance both species-specific ecology and disease intervention factors associated with malaria transmission. Sporozoite infectivity rates, mosquito host blood meal source, bed net coverage and mosquito abundance were assessed in this study. METHODOLOGY: A longitudinal survey was conducted in four villages in two regions of Tanzania. Malaria vectors were sampled using the CDC light trap and pyrethrum spray catch methods. In each village, ten paired houses were selected for mosquitoes sampling. Sampling was done in fortnight case and study was undertaken for six months in both Kilimanjaro (Northern Tanzania) and Dodoma (Central Tanzania) regions. RESULTS: A total of 6,883 mosquitoes were collected including: 5,628 (81.8%) Anopheles arabiensis, 1,100 (15.9%) Culex quinquefasciatus, 89 (1.4%) Anopheles funestus, and 66 (0.9%) Anopheles gambiae s.s. Of the total mosquitoes collected 3,861 were captured by CDC light trap and 3,022 by the pyrethrum spray catch method. The overall light trap: spray catch ratio was 1.3:1. Mosquito densities per room were 96.5 and 75.5 for light trap and pyrethrum spray catch respectively. Mosquito infectivity rates between villages that have high proportion of bed net owners and those without bed nets was significant (P < 0.001) and there was a significant difference in sporozoite rates between households with and without bed nets in these four villages (P < 0.001). CONCLUSION: Malaria remains a major problem in the study areas characterized as low transmission sites. Further studies are required to establish the annual entomological inoculation rates and to observe the annual parasitaemia dynamics in these communities. Outdoor mosquitoes collection should also be considered.

Potential impact of host immunity on malaria treatment outcome in Tanzanian children infected with Plasmodium falciparum.

BACKGROUND: In malaria endemic areas children may recover from malaria after chemotherapy in spite of harbouring genotypically drug-resistant Plasmodium falciparum. This phenomenon suggests that there is a synergy between drug treatment and acquired immunity. This hypothesis was examined in an area of moderately intense transmission of P. falciparum in Tanzania during a drug trail with sulphadoxine-pyrimethamine (SP) or amodiaquine (AQ). METHODS: One hundred children with uncomplicated malaria were treated with either SP or AQ and followed for 28 days. Mutations in parasite genes related to SP and AQ-resistance as well as human sickle cell trait and alpha-thalassaemia were determined using PCR and sequence-specific oligonucleotide probes and enzyme-linked immunosorbent assay (SSOP-ELISA), and IgG antibody responses to a panel of P. falciparum antigens were assessed and related to treatment outcome. RESULTS: Parasitological or clinical treatment failure (TF) was observed in 68% and 38% of children receiving SP or AQ, respectively. In those with adequate clinical and parasitological response (ACPR) compared to children with TF, and for both treatment regimens, prevalence and levels of anti-Glutamate-rich Protein (GLURP)-specific IgG antibodies were significantly higher (P < 0.001), while prevalence of parasite haplotypes associated with SP and AQ resistance was lower (P = 0.02 and P = 0.07, respectively). Interestingly, anti-GLURP-IgG antibodies were more strongly associated with treatment outcome than parasite resistant haplotypes, while the IgG responses to none of the other 11 malaria antigens were not significantly associated with ACPR. CONCLUSION: These findings suggest that GLURP-specific IgG antibodies in this setting contribute to clearance of drug-resistant infections and support the hypothesis that acquired immunity enhances the clinical efficacy of drug therapy. The results should be confirmed in larger scale with greater sample size and with variation in transmission intensity.

Identification of CRF10_CD viruses among bar and hotel workers in Moshi, Northern Tanzania.

We recently identified an HIV-1 subtype C and D circulating recombinant form (CRF10_CD) in infants in Dar es Salaam, Tanzania. So far, this is the only reported HIV-1 CRF in East Africa. However, evidence for its spread in the adult population is scarce. Here we describe the presence of CRF10_CD in two asymptomatic bar and hotel workers in Moshi, Northern Tanzania. Subgenomic sequences from gag (3'p24-5'p7), env (C2-C5), and the 5' LTR were used for phylogenetic analysis and identification of recombination. Genetic divergence between the CRF10_CD sequences from Moshi suggested that they were contracted from independent sources. A third bar worker was infected with an apparent CRF10_CD/subtype A recombinant virus. Our data indicate that CRF10_CD genomes can be transmitted both vertically and heterosexually.

A simple, high-throughput method to detect Plasmodium falciparum single nucleotide polymorphisms in the dihydrofolate reductase, dihydropteroate synthase, and P. falciparum chloroquine resistance transporter genes using polymerase chain reaction- and enzyme-linked immunosorbent assay-based technology.

Single nucleotide polymorphisms (SNPs) in the Plasmodium falciparum dihydrofolate reductase (dhfr), and dihydropteroate synthetase (dhps), and chloroquine resistance transporter (Pfcrt) genes are used as molecular markers of P. falciparum resistance to sulfadoxine/pyrimethamine and chloroquine. However, to be a practical tool in the surveillance of drug resistance, simpler methods for high-throughput haplotyping are warranted. Here we describe a quick and simple technique that detects dhfr, dhps, and Pfcrt SNPs using polymerase chain reaction (PCR)- and enzyme-linked immunosorbent assay (ELISA)-based technology. Biotinylated PCR products of dhfr, dhps, or Pfcrt were captured on streptavidin-coated microtiter plates and sequence-specific oligonucleotide probes (SSOPs) were hybridized with the PCR products. A stringent washing procedure enabled detection of remaining bound SSOPs and distinguished between the SNPs of dhfr, dhps, and Pfcrt with high specificity. The SSOP-ELISA compared well with a standard PCR-restriction fragment length polymorphism procedure, and gave identical positive results in more than 90% of the P. falciparum slide-positive samples tested. The SSOP-ELISA of all dhfr, dhps, or Pfcrt SNPs on 88 samples can be performed in a single day and provides quick and reproducible results. The system can potentially be modified to detect SNPs in other genes.

HIV type 1 subtypes among bar and hotel workers in Moshi, Tanzania.

The HIV-1 prevalence among bar and hotel workers in Tanzania suggests they are a high-risk group for HIV-1 infection. We determined the HIV-1 subtype of 3'-p24/5'-p7 gag and C2-C5 env sequences from 40 individuals representing this population in Moshi. Genetic patterns composed of A(gag)-A(env), C(gag)-C(env), and D(gag)-D(env) were found in 19 (48.0%), 8 (20.0%), and 3 (8.0%) samples, respectively. The remaining 10 samples (25%) had different subtypes in gag and env, indicative of intersubtype recombinants. Among these recombinants, two contained sequences from HIV-1 subsubtype A2, a new genetic variant in Tanzania. Five bar and hotel workers may have been infected with viruses from a common source, based on phylogenetic analysis. The information obtained by surveillance of HIV-1 subtypes in a high-risk population should be useful in the design and evaluation of behavioral, therapeutic, and vaccine trial interventions aimed at reducing HIV-1 transmission.

Therapeutic efficacy of sulfadoxine-pyrimethamine and prevalence of resistance markers in Tanzania prior to revision of malaria treatment policy: Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase mutations in monitoring in vivo resistance.

Prior to the 2001 malarial treatment policy change in Tanzania, we conducted trials to assess the efficacy of sulfadoxine-pyrimethamine (SP) and the usefulness of molecular markers in monitoring resistance. A total of 383 uncomplicated Plasmodium falciparum malaria patients (between 6 and 59 months old) were treated with SP and their responses were assessed. Mutations in the P. falciparum dihydrofolate reductase (pfdhfr) and dihydropteroate synthase (pfdhps) genes in admission day blood samples were analyzed. Results indicated that 85.6% of the patients showed an adequate clinical response, 9.7% an early treatment failure, and 4.7% a late treatment failure. The quintuple mutant genotype (pfdhfr 51 Ile, 59 Arg, and 108 Asn and pfdhps 437 Gly and 540 Glu) showed an association with treatment outcome (odds ratio = 2.1; 95% confidence interval = 0.94-4.48, P = 0.045). The prevalence of the triple pfdhfr mutant genotype (51 Ile, 59 Arg, and 108 Asn) at a site of high SP resistance (23.6%) was four times higher compared with that observed at sites of moderate SP resistance (6.8-14.4%) (P = 0.000001). The genotype failure index calculated by using this marker was invariable (1.96-2.1) at sites with moderate SP resistance, but varied (3.4) at a site of high SP resistance. In conclusion, our clinical and molecular findings suggest that SP may have a short useful therapeutic life in Tanzania; thus, its adoption as an interim first-line antimalarial drug. The findings also point to the potential of the triple pfdhfr mutant genotype as an early warning tool for increasing SP resistance. These data form the baseline SP efficacy and molecular markers profile in Tanzania prior to the policy change.

Target antigen, age, and duration of antigen exposure independently regulate immunoglobulin G subclass switching in malaria.

The isotype/subclass of immunoglobulin determines antibody function, but rather little is known about factors that direct class switching in vivo. To evaluate factors that might influence the maturation of the antibody response during infection, we conducted a seroepidemiological study of the immunoglobulin G (IgG) subclass response to four merozoite-associated antigens of Plasmodium falciparum in a mountainous region of northeastern Tanzania, where malaria endemicity declines with increasing altitudes. We found that IgG1/IgG3 class switching is independently affected by the nature of the antigen, cumulative exposure to the antigen, and the maturity of the immune system (i.e., the age of the individual). These observations provide insights into the effects of immune system maturity, the duration and intensity of antigen exposure, and inherent characteristics of individual antigens on the process of class switching in human B cells. Our data also throw light on the consequences of class switch decisions on the gradual acquisition of antimalarial immunity.

Altitude-dependent and -independent variations in Plasmodium falciparum prevalence in northeastern Tanzania.

BACKGROUND: Effective malaria control requires information about intensity of transmission across large areas and populations. Estimates based on entomological factors lack precision and are not cost-effective to obtain. We tested altitude and rainfall measurements as correlates of transmission intensity in different ecological settings. METHODS: We conducted 2 cross-sectional surveys of approximately 12,000 people (1-45 years old) in 6 altitude transects (150-1800 m) in the Kilimanjaro and Tanga regions of Tanzania. Data were analyzed for associations with altitude and rainfall estimates by use of appropriate regression models. RESULTS: Plasmodium falciparum prevalence showed a negative relationship with altitude (19% and 21% decrease/100-m altitude increase, respectively, in children in Kilimanjaro and Tanga) and rainfall during the 3 months before the survey (46% decrease/100-mm rainfall increase in children in Kilimanjaro). Mean hemoglobin concentrations increased with altitude (0.05 and 0.09 g/dL/100-m altitude increase, respectively, in children in Kilimanjaro and Tanga) and rainfall (0.17 g/dL/100-mm rainfall increase in children and adults in Kilimanjaro). DISCUSSION: Altitude and rainfall were correlated with parasite prevalence and mean hemoglobin concentration; however, the relationship varied according to ecological setting. Climatological variables alone cannot predict malarial outcomes. Local variations in seasonality of malaria transmission--together with vector species composition, topography, host and parasite genetics, and socioeconomic factors--may influence malaria prevalence.