Development of a high-throughput diagnostic screening tool to monitor the status of pyrethroid resistance in the cattle tick, Rhipicephalus microplus

Abstract

Rhipicephalus microplus is a major ectoparasite of cattle that causes large economic losses. This is due to the diseases it transmits resulting in high mortality and morbidity in bovines, as well as indirect losses such as a reduced milk and meat yield, damage to hides and secondary infections which increase the need for use of antibiotics. Synthetic pyrethroids, formamidines, carbamates and organophosphates are commonly used in Africa to control the R. microplus population, as these acaricides are the most cost-effective ways to combat high tick loads. However, R. microplus has developed resistance to the above mentioned chemical acaricides. In order to overcome this problem an effective tick control strategy with rapid access to the resistance status of a population is required to enable knowledge-based selection of a suitable acaricide. This study provides an update on the resistance status of R. microplus to synthetic pyrethroids in the farming community of Mnisi, Mpumalanga, South Africa using conventional single nucleotide polymorphism (SNP) analyses. A high-throughput method of identifying the resistance status of R. microplus cattle ticks to synthetic pyrethroids by making use of TaqMan® genotyping technology is also proposed. The TaqMan® assays make use of SNPs located in the voltage-gated sodium channel gene that have been linked to resistance. Field samples were collected, and genomic DNA was extracted for PCR, sequencing, and species identification. Positive controls and genomic DNA of known genotype were used to evaluate the accuracy of the TaqMan® assays. From the conventional SNP analyses, it is evident that there is a high level of resistance in R. microplus to synthetic pyrethroids in the Mnisi communal area. The TaqMan® assays as a high-throughput detection has potential for commercialization but still requires further optimization.