When a discriminating dose assay is not enough: measuring the intensity of insecticide resistance in malaria vectors

Bagi, Judit, Grisales, Nelson, Corkill, Rebecca, Morgan, John, N’Falé, Sagnon, Brogdon, William G and Ranson, Hilary ORCID: https://orcid.org/0000-0003-2332-8247 (2015) 'When a discriminating dose assay is not enough: measuring the intensity of insecticide resistance in malaria vectors'. Malaria Journal, Vol 14, e210.

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Abstract

Background

Guidelines from the World Health Organization for monitoring insecticide resistance in disease vectors recommend exposing insects to a predetermined discriminating dose of insecticide and recording the percentage mortality in the population. This standardized methodology has been widely adopted for malaria vectors and has provided valuable data on the spread and prevalence of resistance. However, understanding the potential impact of this resistance on malaria control requires a more quantitative measure of the strength or intensity of this resistance.

Methods

Bioassays were adapted to quantify the level of resistance to permethrin in laboratory colonies and field populations of Anopheles gambiae sensu lato. WHO susceptibility tube assays were used to produce data on mortality versus exposure time and CDC bottle bioassays were used to generate dose response data sets. A modified version of the CDC bottle bioassay, known as the Resistance Intensity Rapid Diagnostic Test (I-RDT), was also used to measure the knockdown and mortality after exposure to different multipliers of the diagnostic dose. Finally cone bioassays were used to assess mortality after exposure to insecticide treated nets.

Results

The time response assays were simple to perform but not suitable for highly resistant populations. After initial problems with stability of insecticide and bottle washing were resolved, the CDC bottle bioassay provided a reproducible, quantitative measure of resistance but there were challenges performing this under field conditions. The I-RDT was simple to perform and interpret although the end point selected (immediate knockdown versus 24 h mortality) could dramatically affect the interpretation of the data. The utility of the cone bioassays was dependent on net type and thus appropriate controls are needed to interpret the operational significance of these data sets.

Conclusions

Incorporating quantitative measures of resistance strength, and utilizing bioassays with field doses of insecticides, will help interpret the possible impact of resistance on vector control activities. Each method tested had different benefits and challenges and agreement on a common methodology would be beneficial so that data are generated in a standardized format. This type of quantitative data are an important prerequisite to linking resistance strength to epidemiological outcomes.

Item Type:	Article
Additional Information:	The electronic version of this article is the complete one and can be found online at: http://www.malariajournal.com/content/14/1/210
Subjects:	QX Parasitology > QX 20 Research (General) QX Parasitology > Insects. Other Parasites > QX 600 Insect control. Tick control QX Parasitology > Insects. Other Parasites > QX 650 Insect vectors WA Public Health > Preventive Medicine > WA 110 Prevention and control of communicable diseases. Transmission of infectious diseases WA Public Health > Preventive Medicine > WA 240 Disinfection. Disinfestation. Pesticides (including diseases caused by) WC Communicable Diseases > Tropical and Parasitic Diseases > WC 750 Malaria
Faculty: Department:	Biological Sciences > Vector Biology Department
Digital Object Identifer (DOI):	https://doi.org/10.1186/s12936-015-0721-4
Depositing User:	Lynn Roberts-Maloney
Date Deposited:	25 Jun 2015 08:35
Last Modified:	24 Jun 2022 10:28
URI:	https://archive.lstmed.ac.uk/id/eprint/5223

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