Acetylcholinesterase 1 of the cattle tick, Rhipicephalus (Boophilus) annulatus (Say)

Authors: Temeyer, Kevin; Schlechte, Kristie; Saelao, Perot; Olafson, Pia; Lohmeyer, Kimberly

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2026
Publication Date: 2/24/2026
Citation: Temeyer, K.B., Schlechte, K.G., Saelao, P., Olafson, P.U., Lohmeyer, K.H. 2026. Acetylcholinesterase 1 of the cattle tick, Rhipicephalus (Boophilus) annulatus (Say). Journal of Medical Entomology. 63(1). https://doi.org/10.1093/jme/tjag025.
DOI: https://doi.org/10.1093/jme/tjag025

Interpretive Summary: The cattle fever ticks Rhipicephalus microplus and Rhipicephalus annulatus transmit pathogens responsible for bovine babesiosis and anaplasmosis. Although these ticks were eradicated from the United States, they and the pathogens they transmit remain endemic in Mexico and other countries, and continue to pose a serious risk to the U.S. cattle industry. Imported cattle are inspected and treated with acaricide to prevent reentry of these ticks and pathogens into the United States. Outbreak cattle fever tick infestations within the United States are eradicated under the Cattle Fever Tick Eradication Program administered through the Veterinary Services Division of the Animal and Plant Health Inspection Service (APHIS) of the U.S. Department of Agriculture in cooperation with animal health agencies of various states. The acaricide of first choice for treatment of imported cattle and eradication of outbreak infestations is the organophosphate, coumaphos, which kills ticks by inactivating acetylcholinesterase (AChE), an enzyme vital to function of the tick central nervous system. New research reports discovery of alternative splicing giving rise to alternate isoforms of acetylcholinesterase 1 of Rhipicephalus annulatus, adding to the known complexity of AChEs in cattle fever ticks and providing further evidence of the key role of cholinergic systems in tick physiology and development. It is expected that increased understanding and targeting of the key functional roles of tick cholinergic systems may enable further advances in the development of new and improved tick control technologies.

Technical Abstract: The cattle fever ticks Rhipicephalus microplus and Rhipicephalus annulatus transmit pathogens responsible for bovine babesiosis and anaplasmosis. Although eradicated from the United States, these ticks and the pathogens they transmit are endemic in Mexico and other countries, and pose a serious risk to the U.S. cattle industry. Cattle imported into the U.S. are inspected and treated with an acaricide, coumaphos, to prevent tick reentry into the U.S. Coumaphos is an organophosphate (OP) that kills ticks by inactivating acetylcholinesterase (AChE), an enzyme vital to the tick central nervous system. Previous research has extensively studied the AChEs of R. microplus, however there has been much less study in R. annulatus. The present work reports the cloning, sequencing and baculoviral expression of recombinant AChE1s of R. annulatus, including the discovery of three different RannAChE1 isoforms that are produced by alternative splicing of a single locus. Similar AChE kinetic activities were observed for the three isoforms, and these were comparable to AChE1 of R. microplus. Further, incorporation of a G170S substitution, homologous to the G119S mutation in mosquitos that affords resistance to OP inhibition, resulted in reduced sensitivity of RannAChE1-1 to inhibition by oxon forms of OPs. This underscores the complexity of AChEs in cattle fever ticks and provides further evidence of the key role of cholinergic systems in tick physiology and development.