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Use of alternative bioassays to explore the impact of pyrethroid resistance on LLIN efficacy.

Publication ,  Journal Article
Grossman, MK; Oliver, SV; Brooke, BD; Thomas, MB
Published in: Parasit Vectors
April 7, 2020

BACKGROUND: There is substantial concern that the spread of insecticide resistance will render long-lasting insecticide-treated nets (LLINs) ineffective. However, there is limited evidence supporting a clear association between insecticide resistance and malaria incidence or prevalence in the field. We suggest that one reason for this disconnect is that the standard WHO assays used in surveillance to classify mosquito populations as resistant are not designed to determine how resistance might impact LLIN efficacy. The standard assays expose young, unfed female mosquitoes to a diagnostic insecticide dose in a single, forced exposure, whereas in the field, mosquitoes vary in their age, blood-feeding status, and the frequency or intensity of LLIN exposure. These more realistic conditions could ultimately impact the capacity of "resistant" mosquitoes to transmit malaria. METHODS: Here, we test this hypothesis using two different assays that allow female mosquitoes to contact a LLIN as they host-seek and blood-feed. We quantified mortality after both single and multiple exposures, using seven different strains of Anopheles ranging in pyrethroid resistance intensity. RESULTS: We found that strains classified as 1×-resistant to the pyrethroid insecticide deltamethrin in the standard WHO assay exhibited > 90% mortality over 24 h following more realistic LLIN contact. Mosquitoes that were able to blood-feed had increased survival compared to their unfed counterparts, but none of the 1×-resistant strains survived for 12 days post-exposure (the typical period for malaria parasite development within the mosquito). Mosquitoes that were 5×- and 10×-resistant (i.e. moderate or high intensity resistance based on the WHO assays) survived a single LLIN exposure well. However, only about 2-3% of these mosquitoes survived multiple exposures over the course of 12 days and successfully blood-fed during the last exposure. CONCLUSIONS: These results suggest that the standard assays provide limited insight into how resistance might impact LLIN efficacy. In our laboratory setting, there appears little functional consequence of 1×-resistance and even mosquitoes with moderate (5×) or high (10×) intensity resistance can suffer substantial reduction in transmission potential. Monitoring efforts should focus on better characterizing intensity of resistance to inform resistance management strategies and prioritize deployment of next generation vector control products.

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Published In

Parasit Vectors

DOI

EISSN

1756-3305

Publication Date

April 7, 2020

Volume

13

Issue

1

Start / End Page

179

Location

England

Related Subject Headings

  • Tropical Medicine
  • Mycology & Parasitology
  • Mosquito Vectors
  • Mosquito Control
  • Insecticides
  • Insecticide-Treated Bednets
  • Insecticide Resistance
  • Female
  • Biological Assay
  • Behavior, Animal
 

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Grossman, M. K., Oliver, S. V., Brooke, B. D., & Thomas, M. B. (2020). Use of alternative bioassays to explore the impact of pyrethroid resistance on LLIN efficacy. Parasit Vectors, 13(1), 179. https://doi.org/10.1186/s13071-020-04055-9
Grossman, Marissa K., Shüné V. Oliver, Basil D. Brooke, and Matthew B. Thomas. “Use of alternative bioassays to explore the impact of pyrethroid resistance on LLIN efficacy.Parasit Vectors 13, no. 1 (April 7, 2020): 179. https://doi.org/10.1186/s13071-020-04055-9.
Grossman MK, Oliver SV, Brooke BD, Thomas MB. Use of alternative bioassays to explore the impact of pyrethroid resistance on LLIN efficacy. Parasit Vectors. 2020 Apr 7;13(1):179.
Grossman, Marissa K., et al. “Use of alternative bioassays to explore the impact of pyrethroid resistance on LLIN efficacy.Parasit Vectors, vol. 13, no. 1, Apr. 2020, p. 179. Pubmed, doi:10.1186/s13071-020-04055-9.
Grossman MK, Oliver SV, Brooke BD, Thomas MB. Use of alternative bioassays to explore the impact of pyrethroid resistance on LLIN efficacy. Parasit Vectors. 2020 Apr 7;13(1):179.
Journal cover image

Published In

Parasit Vectors

DOI

EISSN

1756-3305

Publication Date

April 7, 2020

Volume

13

Issue

1

Start / End Page

179

Location

England

Related Subject Headings

  • Tropical Medicine
  • Mycology & Parasitology
  • Mosquito Vectors
  • Mosquito Control
  • Insecticides
  • Insecticide-Treated Bednets
  • Insecticide Resistance
  • Female
  • Biological Assay
  • Behavior, Animal