Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
[Preprint]. 2023 Aug 5:2023.07.31.23293323.
doi: 10.1101/2023.07.31.23293323.

LLIN Evaluation in Uganda Project (LLINEUP) - Plasmodium infection prevalence and genotypic markers of insecticide resistance in Anopheles vectors from 48 districts of Uganda

Affiliations

LLIN Evaluation in Uganda Project (LLINEUP) - Plasmodium infection prevalence and genotypic markers of insecticide resistance in Anopheles vectors from 48 districts of Uganda

Amy Lynd et al. medRxiv. .

Update in

Abstract

Background: In 2017-2019, we conducted a large-scale, cluster-randomised trial (LLINEUP) to evaluate long-lasting insecticidal nets (LLINs) treated with a pyrethroid insecticide plus the synergist piperonyl butoxide (PBO LLINs), as compared to conventional, pyrethroid-only LLINs across 104 health sub-districts (HSDs) in Uganda. In LLINEUP, and similar trials in Tanzania, PBO LLINs were found to provide greater protection against malaria than conventional LLINs, reducing parasitaemia and vector density. In the LLINEUP trial, cross-sectional entomological surveys were carried out at baseline and then every 6 months for two years. In each survey, ten households per HSD were randomly selected for indoor household entomological collections.

Results: Overall, 5395 female Anopheles mosquitoes were collected from 5046 households. The proportion of mosquitoes infected with Plasmodium falciparum did not change significantly over time, while infection with non-falciparum malaria decreased in An. gambiae s.s, but not An. funestus. The frequency of genetic markers associated with pyrethroid resistance increased significantly over time, but the rate of change was not different between the two LLIN types. The knock-down resistance (kdr) mutation Vgsc-995S declined over time as Vgsc-995F, the alternative resistance mutation at this codon, increased. Vgsc-995F appears to be spreading into Uganda.

Conclusions: Distribution of LLINs in Uganda was associated with reductions in parasite prevalence and vector density, but the proportion of infective mosquitoes remained stable, suggesting that the potential for transmission persisted. The increased frequency of markers of pyrethroid resistance indicates that LLIN distribution favoured the evolution of resistance within local vectors and highlights the potential benefits of resistance management strategies.Trial registration:: This study is registered with ISRCTN, ISRCTN17516395. Registered 14 February 2017, http://www.isrctn.com/ISRCTN17516395.

Keywords: Uganda; cluster-randomised trial; insecticide resistance; long-lasting insecticidal nets (LLINs); malaria; piperonyl butoxide (PBO); vector control.

PubMed Disclaimer

Conflict of interest statement

Competing interests The authors declare that they have no competing interests.

Figures

Figure. 1:
Figure. 1:
Map of mosquito collection locations within the LLINEUP cluster-randomised control trial. Intervention arm is indicated by colour with the 14 clusters which were omitted during final collection round (25 months post LLIN distribution) indicated with hatched shading.
Figure 2.
Figure 2.
Plasmodium infection prevalence in An. gambiae and An. funestus. Point prevalence estimate is shown with associated 95%CIs. Data were collected simultaneously but are plotted offset for ease of viewing. Round 1 was the baseline collection with follow up rounds at approximately six-monthly intervals (see text).
Figure. 3:
Figure. 3:
Insecticide resistance marker prevalence in Anopheles gambiae s.s. across the baseline and four post LLIN distribution collection rounds. Markers in green external boxes show significant increases (see Table 3) over the course of the trial, red boxes indicate significant decreases (Table 3). Dashed line indicates significant change observed only when GLMM included all five collection points.
Figure. 4:
Figure. 4:
Mapping of mutant allele frequencies over collection rounds for Vgsc-995F, Cyp6p4-236M and Cyp4j5-43F. X and Y axis tickmarks show longitude and latitude respectively. Note colour scales do not carry over across rows.

References

    1. Abeku TA, Helinski MEH, Kirby MJ, Ssekitooleko J, Bass C, Kyomuhangi I, Okia M et al. (2017) Insecticide resistance patterns in Uganda and the effect of indoor residual spraying with bendiocarb on kdr L1014S frequencies in Anopheles gambiae ss. Malaria Journal, 16, 1–11. - PMC - PubMed
    1. Abrams PA (1993) Does increased mortality favor the evolution of more rapid senescence. Evolution, 47, 877–887. - PubMed
    1. Bass C, Nikou D, Blagborough AM, Vontas J, Sinden RE, Williamson MS, Field LM (2008) PCR-based detection of Plasmodium in Anopheles mosquitoes: a comparison of a new high-throughput assay with existing methods. Malaria journal, 7, 1–9. - PMC - PubMed
    1. Bass C, Nikou D, Donnelly MJ, Williamson MS, Ranson H, Ball A, Vontas J et al. (2007) Detection of knockdown resistance (kdr) mutations in Anopheles gambiae: a comparison of two new high-throughput assays with existing methods. Malaria Journal, 6, 1–14. - PMC - PubMed
    1. Bhatt S, Weiss DJ, Cameron E, Bisanzio D, Mappin B, Dalrymple U, Battle KE et al. (2015) The effect of malaria control on Plasmodium falciparum in Africa between 2000 and 2015. Nature, 526, 207–211. - PMC - PubMed

Publication types