Presentation at 65th Annual meeting of the American Society of Tropical Medicine and Hygiene

Impact of combining Indoor Residual Spraying and Long-Lasting Insecticidal Nets on Anopheles arabiensis in Ethiopia: Preliminary findings of a randomized controlled trial

Oljira Kenea, Meshesha Balkew, Habte Tekie, Teshome Gebre-Michael, Wakgari Deressa, Eskindir Loha, Hans J. Overgaard, Bernt Lindtjørn

Abstract

The current malaria vector control interventions, indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) have been used in combination in sub-Saharan Africa with inconclusive evidence that the combined intervention is more effective than either IRS or LLINs alone. In Ethiopia, both interventions target Anopheles arabiensis, the sole primary malaria vector. This study compared the impact of combining IRS and LLINs with either intervention alone in south-central Ethiopia. Villages were randomly allocated to four study arms: IRS + LLIN, IRS, LLIN, and control. LLINs (PermaNet 2.0) were provided free of charge. IRS with propoxur was applied before the main malaria transmission season in 2014 and 2015. Adult mosquitoes were collected in randomly selected villages in each arm using CDC light trap catch (LTC) set close to a sleeping person, pyrethrum spray catch (PSC), and artificial pit shelter (PIT), for measuring host-seeking density (HSD), indoor resting density (IRD), and outdoor resting density (ORD). Human landing catch (HLC) was performed in selected villages to monitor An. arabiensis biting behaviors. Mean densities were compared using incidence rate ratio (IRR) calculated by negative binomial regression. A total of 1786 female anophelines of four species was collected of which An. arabiensis (n=574) was highest in the control arm (51.4%) followed by LLIN (31.5%), IRS (9.2%), and IRS+LLIN (7.9%). The mean HSD of An. arabiensis in the IRS+LLIN arm was similar to either the IRS arm (0.03 vs. 0.03/ house/LTC/night) or the LLIN arm (0.03 vs. 0.10/house/LTC/night, p=0.07) and so was the difference in IRD and ORD between the IRS and LLIN compared to the IRS arm. However, both IRD and ORD were higher in LLIN compared to IRS+LLIN (p < 0.001 for indoors). In all study arms, An. arabiensis was actively biting indoors and outdoors throughout the night with an early night biting peak before the local people retire to bed. IRS+LLIN compared to IRS had equal powerful impact on resting density of An. arabiensis, but LLIN had the least impact.

The poor use bed nets less for malaria protection

Hailu A, Lindtjørn B, Deressa W, Gari T, Loha E, Robberstad B. Equity in long-lasting insecticidal nets and indoor residual spraying for malaria prevention in a rural South Central Ethiopia. Malaria Journal 2016; 15(1): 1-11.

Background: While recognizing the recent achievement in the global fight against malaria, the disease remains a challenge to health systems in low-income countries. Beyond widespread consensuses about prioritizing malaria prevention, little is known about the prevailing status of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) across different levels of wealth strata. The aim of this study was to evaluate the socioeconomic related dimension of inequalities in malaria prevention interventions.

Methods: This study was conducted in July–August 2014 in Adami Tullu district in the South-central Ethiopia, among 6069 households. A cross-sectional data were collected on household characteristics, LLIN ownership and IRS coverage. Principal component analysis technique was used for ranking households based on socioeconomic position. The inequality was measured using concentration indices and concentration curve. Decomposition method was employed in order to quantify the percentage contribution of each socioeconomic related variable on the overall inequality.

Results: The proportion of households with at least one LLIN was 11.6 % and IRS coverage was 72.5 %. The Erreygers normalized concentration index was 0.0627 for LLIN and 0.0383 for IRS. Inequality in LLIN ownership was mainly associated with difference in housing situation, household size and access to mass-media and telecommunication service.

Conclusion: Coverage of LLIN was low and significant more likely to be owned by the rich households, whereas houses were sprayed equitably. The current mass free distribution of LLINs should be followed by periodic refill based on continuous monitoring data.