The effectiveness of older insecticide-treated bed nets (ITNs) to prevent malaria infection in an area of moderate pyrethroid resistance: results from a cohort study in Malawi

Abstract

Background: A previous cohort study in Malawi showed that users of new insecticide-treated bed nets (ITNs) were significantly protected against malaria compared to non-users, despite moderate levels of pyrethroid resistance among the primary mosquito vectors. The present study investigated whether ITNs that were 1-2 years old continued to protect users in the same area with moderate pyrethroid resistance. Methods: One year following a baseline cross-sectional malaria parasitaemia prevalence survey and universal distribution of deltamethrin ITNs (May 2012), a fixed cohort of 1223 children aged 6-59 months was enrolled (April 2013). Children were tested for parasitaemia at monthly scheduled visits and at unscheduled sick visits from May to December 2013 using rapid diagnostic tests. ITN use the prior night and the condition of ITNs (based on presence of holes) was assessed by caregiver self-report. The incidence rate ratio (RR) comparing malaria infection among users and non-users of ITNs was modelled using generalized estimating equations adjusting for potential confounders and accounting for repeated measures on each child. The protective efficacy (PE) of ITN use was calculated as 1 − RR. Results: In this cohort, self-reported ITN use remained consistently high (> 95%) over the study period. Although users of ITNs were slightly more protected compared to non-users of ITNs, the difference in incidence of infection was not statistically significant (RR 0.83, 95% confidence interval [CI] 0.54-1.27). Among ITN users, malaria incidence was significantly lower in users of ITNs with no holes (of any size) compared to users of ITNs with ≥ 1 hole (RR 0.82, 95% CI 0.69-0.98). Conclusions: There was no significant PE of using 1-2 year-old ITNs on the incidence of malaria in children in an area of moderate pyrethroid resistance, but among ITN users, the authors found increased protection by ITNs with no holes compared to ITNs with holes. Given the moderate levels of pyrethroid resistance in the primary malaria vector and recent evidence of added benefits of ITNs with synergists or non-pyrethroid insecticides, next-generation ITNs may be a useful strategy to address pyrethroid resistance and should be further explored in Malawi.

Insecticide Treated Net Ownership, Utilization and Knowledge of Malaria in Children Residing in Batoke-Limbe, Mount Cameroon Area: Effect on Malariometric and Haematological Indices

“…However, there are also concerns on the increasing pyrethroid resistance which is likely to affect LLINs e cacy in preventing malaria parasite infection. Even though a study in Cameroon [15] as well as various studies in Malawi [16], Benin [17,18] and several countries in Africa [19] reported that LLIN still offers some protection even in areas of high pyrethroid resistance, there is need for continuous surveillance and evaluation on the effective use of LLINs distributed by the Cameroon government and its partners to reduce malaria mortality and morbidity.…”

Narrative Review on Health-EDRM Primary Prevention Measures for Vector-Borne Diseases

“…Inadequate information can lead to the improper maintenance of vector-prevention commodities, subsequently compromising their efficacy. For example, damaged bed nets with holes and improper bed net usage have been shown to lead to outcomes worse than no usage at all [ 64 , 65 , 66 ]. Some measures may also be affected by other health conditions, such as allergic reactions to insect repellent active ingredients [ 76 ], while others may be limited by cultural concerns, as demonstrated in the case of vaccination hesitancy in certain religious communities [ 81 , 82 ].…”

“…Physical deterioration [ 64 , 65 , 66 ]: Damaged bed nets have significantly reduced efficacies. Proper maintenance of bed nets is important.…”

Reduced long-lasting insecticidal net efficacy and pyrethroid insecticide resistance are associated with over-expression ofCYP6P4, CYP6P3andCYP6Z1in populations ofAnopheles coluzziifrom South-East Côte d’Ivoire

“…Other observational cohorts have reported higher incidences of malaria among non-net users compared to users in areas of moderate to high pyrethroid resistance [17]. The extent of protective efficacy afforded by pyrethroid LLINs will likely reflect the strength of local vector resistance and levels of both net physical integrity and individual compliance [32,33]. However, in Côte d'Ivoire, reported LLIN usage has been low, requiring additional behavioural interventions [2,34].…”