SNP Analysis Infers that Recombination Is Involved in the Evolution of Amitraz Resistance in Rhipicephalus microplus.

Ulrike Gertrud Munderloh,Samantha Baron,Christine Maritz-Olivier,Nicolaas A Van Der Merwe,Maxime Madder

doi:10.1371/journal.pone.0131341

Ulrike Gertrud Munderloh, Samantha Baron + Show 3 more

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https://doi.org/10.1371/journal.pone.0131341

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Abstract

Rhipicephalus microplus, better known as the Asiatic cattle tick, is a largely invasive ectoparasite of great economic importance due to the negative effect it has on agricultural livestock on a global scale, particularly cattle. Tick-borne diseases (babesiosis and anaplasmosis) transmitted by R. microplus are alarming as they decrease the quality of livestock health and production. In sub-Saharan Africa, cattle represent a major source of meat and milk, but this region of the world is severely affected by the Rhipicephalus microplus tick. The principal method for tick control is the use of chemical acaricides, notably amitraz, which was implemented in the 1990’s after resistance to other acaricides surfaced. However, the efficiency of chemical control is hindered by an increase in the frequency of mutant resistance alleles to amitraz in tick populations. Presently, the only way to assess amitraz resistance is by means of larval packet tests, but this technique is time-consuming and not particularly cost effective. The main aims of this study were three-fold. First, we attempted to correlate two known SNPs in the octopamine/tyramine (OCT/Tyr) receptor with amitraz resistance in South African field samples of R. microplus. Second, we calculated gametic disequilibrium for these SNPs to determine whether they are randomly associated. Lastly, we conducted a study to assess the evolutionary effects of recombination within the OCT/Tyr receptor. Our results confirmed that the two SNPs are associated with amitraz resistance in the South African tick strain, and that they are in gametic disequilibrium. Additionally, recombination was detected in the OCT/Tyr receptor generating two recombinant haplotypes. These results are of concern to farmers in sub-Saharan Africa, and the emergence of amitraz resistance should be closely monitored in future. Therefore, we present a quick and affordable RFLP based diagnostic technique to assess amitraz resistance in field samples of R. microplus.

Highlights

Rhipicephalus microplus ticks are hematophagous ectoparasites of veterinary importance, and are capable of parasitizing a variety of hosts, cattle are their primary preference [1]
We have investigated the evolution of amitraz resistance in South African Rhipicephalus microplus ticks
We exploited the high level of gametic disequilibrium between these two SNPs and an additional SNP, which changes a restriction enzyme binding site, in order to devise an affordable an easy restriction enzyme based assessment tool for amitraz resistance in field samples of ticks

Summary

Introduction

Rhipicephalus microplus ticks are hematophagous ectoparasites of veterinary importance, and are capable of parasitizing a variety of hosts, cattle are their primary preference [1]. These ticks are adept in transmitting a variety of tick-borne pathogens to cattle, most notably Babesia bovis, which causes Asiatic babesiosis or redwater [1, 2]. The use of chemical acaricides is still the most preferred method for tick control, but has become less effective due to the emergence of resistance. Resistance to acaricides has been attributed to target site insensitivity as well as metabolic detoxification, depending on the mode of action of the acaricide

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