CDC light traps underestimate the protective efficacy of an indoor spatial repellent against bites from wild Anopheles arabiensis mosquitoes in Tanzania

Johnson Kyeba Swai; Ummi Abdul Kibondo; Watson Samuel Ntabaliba; Hassan Ahamad Ngoyani; Noely Otto Makungwa; Antony Pius Mseka; Madeleine Rose Chura; Thomas Michael Mascari; Sarah Jane Moore

doi:10.1186/s12936-023-04568-5

CDC light traps underestimate the protective efficacy of an indoor spatial repellent against bites from wild Anopheles arabiensis mosquitoes in Tanzania

Malar J. 2023 Apr 29;22(1):141. doi: 10.1186/s12936-023-04568-5.

Authors

Affiliations

¹ Vector Control Product Testing unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania. skyeba@ihi.or.tz.
² Swiss Tropical and Public Health Institute, Allschwil, Switzerland. skyeba@ihi.or.tz.
³ University of Basel, Basel, Switzerland. skyeba@ihi.or.tz.
⁴ Vector Control Product Testing unit, Environmental Health and Ecological Science Department, Ifakara Health Institute, Bagamoyo, Tanzania.
⁵ S. C. Johnson & Son, Inc., Racine, WI, USA.
⁶ S. C. Johnson & Son, Inc., Racine, WI, USA. TMMascar@scj.com.
⁷ Swiss Tropical and Public Health Institute, Allschwil, Switzerland.
⁸ University of Basel, Basel, Switzerland.
⁹ The Nelson Mandela, African Institution of Science and Technology, School of Life Sciences and Bio Engineering, Tengeru, Arusha, United Republic of Tanzania.

Abstract

Background: Methods for evaluating efficacy of core malaria interventions in experimental and operational settings are well established but gaps exist for spatial repellents (SR). The objective of this study was to compare three different techniques: (1) collection of blood-fed mosquitoes (feeding), (2) human landing catch (HLC), and (3) CDC light trap (CDC-LT) collections for measuring the indoor protective efficacy (PE) of the volatile pyrethroid SR product Mosquito Shield^™ METHODS: The PE of Mosquito Shield^™ against a wild population of pyrethroid-resistant Anopheles arabiensis mosquitoes was determined via feeding, HLC, or CDC-LT using four simultaneous 3 by 3 Latin squares (LS) run using 12 experimental huts in Tanzania. On any given night each technique was assigned to two huts with control and two huts with treatment. The LS were run twice over 18 nights to give a sample size of 72 replicates for each technique. Data were analysed by negative binomial regression.

Results: The PE of Mosquito Shield^™ measured as feeding inhibition was 84% (95% confidence interval (CI) 58-94% [Incidence Rate Ratio (IRR) 0.16 (0.06-0.42), p < 0.001]; landing inhibition 77% [64-86%, (IRR 0.23 (0.14-0.36) p < 0.001]; and reduction in numbers collected by CDC-LT 30% (0-56%) [IRR 0.70 (0.44-1.0) p = 0.160]. Analysis of the agreement of the PE measured by each technique relative to HLC indicated no statistical difference in PE measured by feeding inhibition and landing inhibition [IRR 0.73 (0.25-2.12) p = 0.568], but a significant difference in PE measured by CDC-LT and landing inhibition [IRR 3.13 (1.57-6.26) p = 0.001].

Conclusion: HLC gave a similar estimate of PE of Mosquito Shield^™ against An. arabiensis mosquitoes when compared to measuring blood-feeding directly, while CDC-LT underestimated PE relative to the other techniques. The results of this study indicate that CDC-LT could not effectively estimate PE of the indoor spatial repellent in this setting. It is critical to first evaluate the use of CDC-LT (and other tools) in local settings prior to their use in entomological studies when evaluating the impact of indoor SR to ensure that they reflect the true PE of the intervention.

Keywords: Anopheles; Mosquito sampling; Protective efficacy; Spatial repellent; Vector control; Volatile pyrethroid.

MeSH terms

Animals
Anopheles* / physiology
Centers for Disease Control and Prevention, U.S.
Humans
Insect Repellents* / pharmacology
Malaria* / prevention & control
Mosquito Control / methods
Mosquito Vectors
Tanzania
United States

Substances

Insect Repellents