Study of enteric pathogens among children in the tropics and effects of prolonged storage of stool samples.

The study was performed to compare real-time PCR after nucleic acid extraction directly from stool samples as well as from samples stored and transported on Whatman papers or flocked swabs at ambient temperature in the tropics. In addition, the possible suitability for a clear determination of likely aetiological relevance of PCR-based pathogen detections based on cycle threshold (Ct) values was assessed. From 632 Tanzanian children <5 years of age with and without gastrointestinal symptoms, 466 samples were subjected to nucleic acid extraction and real-time PCR for gastrointestinal viral, bacterial and protozoan pathogens. Equal or even higher frequencies of pathogen detections from Whatman papers or flocked swabs were achieved compared with nucleic acid extraction directly from stool samples. Comparison of the Ct values showed no significant difference according to the nucleic acid extraction strategy. Also, the Ct values did not allow a decision whether a detected pathogen was associated with gastrointestinal symptoms.

Genetic Diversity and Protective Efficacy of the RTS,S/AS01 Malaria Vaccine.

BACKGROUND: The RTS,S/AS01 vaccine targets the circumsporozoite protein of Plasmodium falciparum and has partial protective efficacy against clinical and severe malaria disease in infants and children. We investigated whether the vaccine efficacy was specific to certain parasite genotypes at the circumsporozoite protein locus. METHODS: We used polymerase chain reaction-based next-generation sequencing of DNA extracted from samples from 4985 participants to survey circumsporozoite protein polymorphisms. We evaluated the effect that polymorphic positions and haplotypic regions within the circumsporozoite protein had on vaccine efficacy against first episodes of clinical malaria within 1 year after vaccination. RESULTS: In the per-protocol group of 4577 RTS,S/AS01-vaccinated participants and 2335 control-vaccinated participants who were 5 to 17 months of age, the 1-year cumulative vaccine efficacy was 50.3% (95% confidence interval [CI], 34.6 to 62.3) against clinical malaria in which parasites matched the vaccine in the entire circumsporozoite protein C-terminal (139 infections), as compared with 33.4% (95% CI, 29.3 to 37.2) against mismatched malaria (1951 infections) (P=0.04 for differential vaccine efficacy). The vaccine efficacy based on the hazard ratio was 62.7% (95% CI, 51.6 to 71.3) against matched infections versus 54.2% (95% CI, 49.9 to 58.1) against mismatched infections (P=0.06). In the group of infants 6 to 12 weeks of age, there was no evidence of differential allele-specific vaccine efficacy. CONCLUSIONS: These results suggest that among children 5 to 17 months of age, the RTS,S vaccine has greater activity against malaria parasites with the matched circumsporozoite protein allele than against mismatched malaria. The overall vaccine efficacy in this age category will depend on the proportion of matched alleles in the local parasite population; in this trial, less than 10% of parasites had matched alleles. (Funded by the National Institutes of Health and others.).

Pattern and spatial distribution of plague in Lushoto, north-eastern Tanzania.

A review of plague records from 1986 to 2002 and household interviews were carried out in the plague endemic villages to establish a pattern and spatial distribution of the disease in Lushoto district, Tanzania. Spatial data of households and village centres were collected and mapped using a hand held Global Positioning System and Geographical Information System. During the 16-year period, there were 6249 cases of plague of which 5302 (84.8%) were bubonic, 391 (6.3%) septicaemic, and 438 (7.0%) pneumonic forms. A total of 118 (1.9%) cases were not categorized. Females and individuals aged 7-18 years old were the most affected groups accounting for 54.4% (95% CI: 52.4-56.0) and 47.0% (95% CI: 45-49) of all reported cases, respectively. Most cases were found in villages at high altitudes (1700-1900m); and there was a decline in case fatality rate (CFR) in areas that experienced frequent outbreaks. Overall, there was a reduction in mean reporting time (from symptoms onset to admission) to an average of 1.35 days (95% CI: 1.30-1.40) over the years, although this remained high among adult patients (>18 years). Despite the decrease in the number of cases and CFR over the years, our findings indicate that Lushoto district experiences human plague epidemic every year; with areas at high altitudes being more prone to outbreaks. The continued presence of plague in this focus warrants further studies. Nonetheless, our findings provide a platform for development of an epidemic preparedness plan to contain future outbreaks.

Malaria specific mortality in lowlands and highlands of Muheza district, north-eastern Tanzania.

Vital registration of causes of death in Tanzania is incomplete and many deaths occur outside health care settings. Verbal autopsies (VA) are used to determine the underlying cause of death, and the probable diagnosis helps to estimate reasonably cause-specific mortality. In this paper, we report findings of a verbal autopsy survey which involved eight villages in both low and highlands of Muheza district, north-eastern Tanzania. The survey was conducted following a rapid census, which was done to identify households that had lost one or more members within a period of two years from the date of census. Trained research assistants administered VA questionnaires to parents/close relatives. Two physicians reviewed each report independently and a third opinion was sought where there was discordant report between the two. A total of 9,872 households were surveyed and 134 deaths were recorded. A total of 96 (71.6%) deaths were from lowland villages representing high malaria transmission. Majority (72.4%) of the reported deaths occurred at home whilst 32.1% occurred at heath facility settings. Overall, severe malaria was the leading cause accounting for 34.3% of all deaths. Infants were most affected and accounted for 43.5% of the total deaths. Pulmonary tuberculosis ranked second (8.2%) cause of deaths and was exclusively confined to individuals > or = 15 years. Probable cause of death could not be determined in 13.4% of deaths. In conclusion, majority of deaths in rural north-eastern Tanzania occur at home and the immediate causes are usually unknown or not documented. These findings indicate that the verbal autopsy is a useful tool for detecting leading causes of death at community level in the absence of health facility-based data.

Population pharmacokinetics of intramuscular artesunate in African children with severe malaria: implications for a practical dosing regimen.

Parenteral artesunate (ARS) is the drug of choice for the treatment of severe malaria. Pharmacokinetics data on intramuscular ARS are limited with respect to the main treatment group that carries the highest mortality, namely, critically ill children with severe malaria. A population pharmacokinetic study of ARS and dihydroartemisinin (DHA) was conducted from sparse sampling in 70 Tanzanian children of ages 6 months to 11 years. All the children had been admitted with severe falciparum malaria and were treated with intramuscular ARS (2.4 mg/kg at 0, 12, and 24 h). Venous plasma concentration-time profiles were characterized using nonlinear mixed-effects modeling (NONMEM). A one-compartment disposition model accurately described first-dose population pharmacokinetics of ARS and DHA. Body weight significantly affected clearance and apparent volume of distribution (P < 0.001), resulting in lower ARS and DHA exposure levels in smaller children. An adapted dosing regimen including a practical dosing table per weight band is proposed for young children based on the pharmacokinetic model.