A comparative study of the efficacies of chloroquine and a pyrimethamine-dapsone combination in clearing Plasmodium falciparum parasitaemia in school children in Tanzania

Usefulness of a dispensary-based case-control study for assessing morbidity impact of a treated net programme

BACKGROUND

Case-control studies have been proposed as an appropriate tool for health impact evaluation of insecticide-treated nets (ITN) programmes.

METHODS

A dispensary-based case-control study was carried out in one village in Tanzania. Each case of fever and parasitaemia in a child under 5 years was paired with one community and one dispensary control without fever and parasitaemia. Cases and controls were compared with regard to ITN ownership and other factors assessed by a questionnaire. A cross-sectional survey of factors associated with parasitaemia, including ITN use, was carried out during the study. Dispensary attendance rates of the study children were calculated using passive case detection data.

RESULTS

Cases and dispensary controls had higher dispensary attendance rates compared to community controls and children with nets attended more for most of the illness events. A comparison of cases and community controls showed a strong and statistically significant association between untreated net use and being a case (odds ratio [OR] = 2.1, 95% CI : 1.3-3.4). For those with ITN there was a smaller and weaker association between risk of being a case and ITN use (OR =1.4, 95% CI : 0.9-2.2). Comparison of cases and dispensary controls showed no association between untreated or treated nets and the risk of being a case (for treated nets OR = 0.9, 95% CI : 0.5-1.4 and for untreated nets OR = 1.2, 95% CI : 0.7-2.0). These results are contrary to those from the cross-sectional assessment, where children with ITN had a lower prevalence of parasitaemia than those with no nets (OR = 0.5, 95% CI : 0.3-0.9), and also contrary to other assessments of the health impact of ITN in this population.

CONCLUSIONS

The positive association between mild malaria and net ownership is counter-intuitive and best explained by attendance bias, since children with nets attended more frequently for all curative and preventive services at the dispensary than those without nets. Dispensary-based case-control studies may not be appropriate for assessing impact of treated nets on clinical malaria, while cross-sectional surveys might represent an attractive alternative.

Dynamics of multiple Plasmodium falciparum infections in infants in a highly endemic area of Tanzania

The force of infection and recovery rate for malaria in infants in a highly endemic area of Tanzania were analysed using polymerase chain reaction-restriction fragment length polymorphism genotyping of the Plasmodium falciparum msp2 locus in 99 paired blood samples. Overall, new genotypes were acquired at a rate of 0.064 per day, and the average duration of infections was estimated to be 23 d. The highest recovery rates were in children under 4 months of age. The higher susceptibility of infants to clinical malaria in comparison with older children, in areas of very high transmission, may be largely a consequence of the short duration of infections which precludes the establishment of concomitant immunity. The high turnover of infections also implies that infection prevalence and multiplicity approach an equilibrium even in very young children, and calls into question the use of infant conversion rates as a measure of transmission intensity.

Efficacy and safety of CGP 56697 (artemether and benflumetol) compared with chloroquine to treat acute falciparum malaria in Tanzanian children aged 1-5 years

A randomized, open trial involving 260 Tanzanian children, aged 1-5 years, with acute Plasmodium falciparum malaria was conducted to evaluate the efficacy of the combination antimalarial CGP 56697 (artemether and benflumetol), and to compare it with chloroquine, the standard drug used for malaria treatment in the Kilombero area. Children who had received rescue medication within the first 48 h or had a negative slide at the same time were excluded. Seven-day parasitological cure rates were 94% (95% CI 88-97.5) for CGP 56697 and 35.4% (95% CI 25.9-45.8) for chloroquine. Using the same definition, the 14-day parasitological cure rates were 86.4% (95% CI 78.5-92.2) for CGP 56697 and 10.3% (95% CI 5.1-18.1) for chloroquine. Gametocytes were more effectively suppressed by CGP 56697 than by chloroquine. There were no major adverse events with either drug. CGP 56697 is highly efficacious against P. falciparum in this area of Tanzania. The study contributes to the discussion on treatment strategies, particularly whether chloroquine may still fulfil its role as first-line drug in an area of high malaria transmission and very high levels of chloroquine resistance.