10. Effect of insecticide-treated bed nets on the dynamics of multiple Plasmodium falciparum infections

Abstract

The rates of acquisition and loss of individual genotypes belonging to the FC27 family of the Plasmodium falciparum merozoite surface protein 2 (msp2) gene were studied in 120 children aged 5 months to 2.5 years, in a randomized controlled trial of insecticide-treated bed nets (ITNs) in Kiberege village, Tanzania. Analysis of longitudinal changes in positivity for individual alleles in samples collected at intervals of one month indicated that the average duration of infections, allowing for undetected parasite genotypes, was 73 d in those aged C 18 months and 160 d in children aged 218 months, consistent with a shift from acute to chronic infection with age. Overall, 5 1% of genotypes infecting the host were estimated to be detected by polymerase chain reaction-restriction fragment length polymorphism analysis in any one sample of 0.5 PL of packed peripheral blood cells. In children less than 18 months old this sensitivity was 61% (sE=~%) compared with 41% (sE=~%) in older children. Conversely, the rate of appearance of new parasite genotypes was higher in children < 18 months of age than in older children, but this partly reflected the difference in sensitivity. The overall incidence of new infections was estimated to be reduced by 17% in ITN users. There was no statistically significant difference between users and non-users in observed infection multiplicity, sensitivity, recovery rate, or estimated infection rates for individual alleles. This suggests that, in areas of high I? falciparum endemicity, ITNs have little effect on the establishment of chronic malaria infection.

4. Age dependence of the multiplicity of Plasmodium falciparum infections and of other malariological indices in an area of high endemicity

“…falciparum. Using the same microscopy procedures, the sensitivity of microscopy was 72.5% in the study of effects of ITNs (FRASER-HURT et al, 1999). Our other studies did not provide estimates of this sensitivity because no attempt was made in them to amplify parasite deoxyribonucleic acid from microscopically negative samples.…”

“…Analysis of triplets of samples provides one approach (SMITH et al, 1999). We here present another technique using the data collected during the trial of CGP 56697 (IRION et al, 1998), in which blood samples were collected on presentation from patients with uncomplicated malaria, and again 72 h later, and the msp2 locus of I?…”

Prevalence of Pfmdr 1 N86Y and Y184F Alleles is Associated with Recurrent Parasitemia following Treatment of Uncomplicated Malaria with Artemether-Lumefantrine in Nigerian Patients

“…The prevalence of Pfmdr 1 co-mutation was higher in the AR group than in the GTR group, even though a few patients who responded to treatment had co-mutation. The prevalence of co-mutation may be due to the fact that in areas of high endemicity of P. falciparum, human host are often super infected with multiple clones of the parasite (Smith et al, 1999). Pfmdr 1 N86Y+Y184F co-mutation significantly contributed to AL resistant (P<0.001).…”

Force of infection is key to understanding the epidemiology ofPlasmodium falciparummalaria in Papua New Guinean children

“…This imperfect detectability of P. falciparum infections can bias estimates of force of infection and should be allowed for, if the intention is to comprehensively quantify parasite dynamics (9,10,46). We have tested the effect of detectability in the present study, where two blood samples were collected 24 h apart at all cross-sectional time points and the detectability of a given msp2 genotype in a single blood sample was estimated at 79% (24).…”

“…With the wide acceptance of molecular approaches to malaria epidemiology, more precise measures of molecularly determined FOI ( mol FOI) can now be generated by genotyping individual parasite infections (9)(10)(11)(12). When multiple coinfecting parasite clones within one host can be distinguished, a more realistic measurement of FOI is generated, because natural superinfections can be monitored in hosts who already harbor asymptomatic P. falciparum infections (13,14).…”