Genetic and genomic approaches to understanding drug resistance in parasites

Putative target sites in synganglion for novel ixodid tick control strategies

Acaricide resistance is a global problem that has impacts worldwide. Tick populations with broad resistance to all commercially available acaricides have been reported. Since resistance selection in ticks and their role in pathogen transmission to animals and humans result in important economic and public health burden, it is essential to develop new strategies for their control (i.e., novel chemical compounds, vaccines, biological control). The synganglion is the tick central nervous system and it is responsible for synthesizing and releasing signaling molecules with different physiological functions. Synganglion proteins are the targets of the majority of available acaricides. In this review we provide an overview of the mode-of-action and resistance mechanisms against neurotoxic acaricides in ticks, as well as putative target sites in synganglion, as a supporting tool to identify new target proteins and to develop new strategies for tick control.

Acaricide resistance in Rhipicephalus microplus collected from selected districts of Madhya Pradesh, Uttar Pradesh and Punjab states of India

The isolates of Rhipicephalus microplus collected from Madhya Pradesh (MP), Punjab (PJB) and Uttar Pradesh (UP) states of India were characterized using laboratory standardized adult immersion test (AIT) against macrocyclic lactone (ivermectin), synthetic pyrethroids (cypermethrin and deltamethrin), organophosphates (coumaphos and diazinon) and phenylpyrazole compounds (fipronil). Out of the six isolates tested, five isolates except MTH were resistant to deltamethrin and cypermethrin at level II with RF ranging from 16.4 to 24.02 and 7.05 to 13.2, respectively. In case of organophosphates, coumaphos was less effective showing resistance level II (RF 8.52-11.2) in all the six populations compared with diazinon to which three isolates (MHW, RWA and AGS) were resistant at level II. Except MTH, other five isolates were categorized at level I with RF ranging from 1.53 to 3.02 against ivermectin. The phenylpyrazole compound however was found effective, and none of the isolates could survive at a discriminating concentration. The possible strategy for the management of multi-acaricide-resistant ticks in the surveyed districts was discussed in the present study.

Multiple resistance to acaricides in field populations of Rhipicephalus microplus from Rio Grande do Sul state, Southern Brazil

Acaricide resistance is a major obstacle to the control of Rhipicephalus microplus. Historically, the indiscriminate use of chemical compounds has contributed to the selection of populations resistant to different classes of acaricides. Therefore, multiple acaricide resistance is an important threat to the chemical control of the cattle tick. To investigate the occurrence and extent of multiple resistance to acaricides in Southern Brazil we performed larval tests with cypermethrin, chlorpyriphos, amitraz, fipronil and ivermectin on 104 cattle tick field samples from different ranches in Rio Grande do Sul, between the years 2013 and 2015. Adult immersion tests with a commercial formulation mixture of chlorpyriphos and cypermethrin were performed on 75 samples. Four levels of resistance were established according to the mortality of larvae: Level I: mortality between 82% and 95%; Level II: mortality between 57% and 82%; Level III: mortality between 25% and 57%; and Level IV: mortality lower than 25%. Resistance to cypermethrin was detected in 98.08% of the samples evaluated, mostly at resistance level IV. The frequency of samples resistant to amitraz, chlorpyriphos, ivermectin and fipronil was 76.92%, 60.58%, 60.58% and 53.85% respectively. Multiple resistance to three or more compounds was found in 78.85% of the samples. The results obtained in this study are alarming and reveal a new scenario for the challenge of tick control using chemicals. This is an issue of high importance to cattle production systems where this tick is responsible for a high economic impact.