9. Effect of insecticide-treated bed nets on haemoglobin values, prevalence and multiplicity of infection with Plasmodium falciparum in a randomized controlled trial in Tanzania

Abstract

A randomized controlled trial of insecticide-treated bed nets (ITNs) was conducted in an area of high malaria transmission in Tanzania in order to assess the effects of ITNs on infection and anaemia. One hundred and twenty-two children, aged 5 to 24 months, were randomly allocated to 2 groups, one of which received ITNs. Outcome measures were assessed in 6 consecutive months with monthly cross-sectional surveys. These measures were haemoglobin values, Plasmodium falciparum prevalence and density, and multiplicity of infection determined by polymerase chain reaction-restriction fragment length polymorphism analysis (PCR-RFLP) of the msp2 locusThere was a significant increase in mean heamoglobin values and a significant decrease of 16.4% in microscopically determined I?falciparum prevalence in children in the ITN group six months after the start of the trial. Both effects were more pronounced in younger children. However, no significant difference was observed in parasite density or multiplicity of infection among infected children. Comparison with PCR results indicated that microscopically subpatent parasitaemia was more frequently found in children in the ITN group. This, together with the observed similar multiplicity in the 2 groups, suggests that infections are maintained despite ITN use, owing to the chronicity of infections. This study shows that ITNs reduce the risk of anaemia in highly exposed young children. The virtually unchanged multiplicity of infection indicates that the potentially protective concomitant immunity is not compromised.

Hemoglobin concentration in children in a malaria holoendemic area is determined by cumulated Plasmodium falciparum parasite densities.

“…14,32 However, the effects of such repeated abortion of chronic asymptomatic parasitemia on the development of partial antimalarial immunity need to be considered. 33,34 At study-end, the prevalence of parasitemia in children Ͻ 24 months old was lower than in those Ն 24 months (Table 1). This possibly reflected the frequent use of SP treatment in small children, although Hb was lower in children Ͻ 24 months at study-end.…”

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

“…ITNs are clearlv effect&e against anae-mia and parasitaemia as assessed by microscopy (FRASER-HURT et al, 1999), and this effect can only be a consequence of a reduced infection rate. Yet the estimated reduction in infection rate was modest.…”

“…faZciparum malaria (TANNER et al, 1991;SMITH et al, 1993). The design has been described in detail by FRASER-HURT et al (1999). The present analyses involved repeated finger-prick blood samples collected at intervals of one month over a period of 6 months from 60 children initially aged 5 month-2 years and sleeping under ITNs and from 60 children of the same age not sleeping under ITNs.…”

“…typing of &e msp2 l&S oi I? JalcipaAm] was littli affected by provision of ITNs, although the prevalences of both microscopically detectable infection and anaemia were decreased (FRASER-HURT et al, 1999).…”

Contributions of Polyclonal Malaria, Gametocytemia, and Pneumonia to Infant Severe Anemia Incidence in Malaria Hyperendemic Pemba, Tanzania

“…The MOI did not differ by bed net use reported at enrollment (P = 0.397, by chi-square test) as unlike previously reported. 17 Within the age range of 5-18 months (where most observations were made) ( Figure 3A), MOI was constant with age. An MOI of 1 showed a maximum of 55% at three months of age and decreased to approximately 40% by month 5 to month 6 ( Figure 3B).…”