Hyalomma anatolicum resistance against ivermectin and fipronil is associated with indiscriminate use of acaricides in southwestern Balochistan, Pakistan.

Ivermectin and fipronil have been used regularly to control the hard tick Hyalomma anatolicum (Acari: Ixodidae) in domestic ruminants for more than a half-decade in Balochistan, Pakistan. Inappropriate and indiscriminate use of these acaricides has resulted in the development of resistances in tick species. In this work, acaricides (ivermectin and fipronil) resistance was evaluated in H. anatolicum through in vitro and in vivo bioassays in a horse farm of Quetta, Balochistan province, Pakistan. A participatory epidemiological survey was conducted to assess potential risk factors associated with the development of acaricide resistance in H. anatolicum. The results of the epidemiological survey revealed that the horse keepers did not follow the manufacturer's instructions for the use of acaricides and applied indiscriminate doses of acaricides. The results of in vitro bioassays (adult immersion test and larval immersion test) showed that fipronil and ivermectin have protective efficacy against H. anatolicum. The results of in vivo bioassay (adult-tick mortality assay) revealed that fipronil had a higher efficacy (78.16%) than ivermectin (49.94%). More than 80% of tick mortality was not achieved in any bioassays, even for the highest acaricide concentration (100 ppm), which suggests the development of acaricide resistance against fipronil and ivermectin. This study highlights the urgency to implement a country-wide awareness about resistance monitoring and effective tick control. Graphical abstract.