Knockdown resistance mutations are widely distributed in fleas that transmit plague in Madagascar

Hutton, Shelby Marie (2021) Knockdown resistance mutations are widely distributed in fleas that transmit plague in Madagascar. Masters thesis, Northern Arizona University.

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Abstract

Plague remains an important human disease in certain countries of the world, especially Madagascar, where hundreds of human cases occur annually. The disease is caused by Yersinia pestis, a bacterium, and an important vector is the oriental rat flea Xenopsylla cheopis. In Madagascar, synthetic pyrethroids (SPs) have been frequently used for over two decades to control flea populations in human dwellings as a means of preventing plague transmission. With the heavy use of this single chemical class, resistance to SPs has emerged. The most common mechanism of resistance to pyrethroids arises from target site mutations in the voltage-gated sodium channel (VGSC), which have been described in many arthropod species. We investigated the occurrence of these mutations in X. cheopis by sequencing a region within domain II of the VGSC that is known to contain a resistance mutation (L1014F). We collected fleas from 23 locations in five provinces of Madagascar and performed phenotypic testing of individual fleas against 0.05% deltamethrin, 0.75% permethrin, and 4.0% DDT. Adult immersion tests of fleas followed the World Health Organization (WHO) protocol using strips impregnated with insecticide inside a test tube. We then extracted DNA from 1,303 individual X. cheopis. We found two single nucleotide polymorphisms (SNPs) that encode amino acid substitutions at amino acid position 1014, a known SP resistance position: the L1014F SNP was found in 24 of 25 field collections and occurred at a high frequency (83% of all fleas), whereas the L1014H mutation was very low frequency (4% of all fleas) but was spread across 11 field collections in the central highlands of Madagascar. We found a significant linear relationship between the frequency of kdr alleles and the proportion of individuals within each population that survived exposure to deltamethrin (r = 0.56, p = 0.016). To our knowledge, this is the first report of a correlation between a VGSC genotype and an SP resistance phenotype, as well as the first description of the L1014H mutation in fleas. The high frequency of resistance mutations in field-collected X. cheopis and our bioassay results suggest that resistance to SPs is common and widespread in Madagascar. The ability to detect these mutations in flea populations prior to insecticide treatment would be highly valuable for directing flea control efforts. Therefore, we developed a TaqMan PCR assay for public health officials in Madagascar that allows for the rapid detection of kdr mutations in order to maximize flea control efforts and, thus, reduce the transmission of plague to humans.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Fleas; Insecticide Resistance; Knockdown Resistance; Plague; Synthetic Pyrethroids; Vector Control
Subjects:	R Medicine > RC Internal medicine
MeSH Subjects:	C Diseases > C01 Bacterial Infections and Mycoses
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > Biological Sciences
Date Deposited:	01 Mar 2022 17:20
Last Modified:	01 Mar 2022 17:20
URI:	https://openknowledge.nau.edu/id/eprint/5774

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