Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 3, 2005
Publication Date: February 18, 2006
Citation: Pruett Jr., J.H., Pound, J.M. 2006. Biochemical diagnosis of organophosphate-insensitivity with neural acetylcholinesterase extracted by sonication from the adult tick synganglion. Veterinary Parasitology. 135:355-363. Interpretive Summary: The southern cattle tick, Boophilus microplus, transmits Texas cattle fever, caused by a blood-borne parasite, from cow to cow. The southern cattle tick was eradicated from the United States in 1943 after years of an extensive eradication program. To prevent reentry of the southern cattle tick through importation ports on the Texas border the Cattle Fever Tick Surveillance and Quarantine Program has be maintained by the USDA-APHIS/Veterinary Services. All cattle presented at the border port for importation are palpated and visually inspected by tick program inspectors. If free of ticks, they receive a supplemental dip in the organophosphate, coumaphos. They are then certified and released for entry into the United States. The program is very dependent upon the effectiveness of coumaphos for control of the tick. Reports of resistance to organophosphates in Mexican tick populations raise concerns about loss of coumaphos for control. Currently ticks that survive pesticide treatment and are collected at the importation ports, are sent to the USDA-ARS Cattle Fever Tick Research Laboratory in Mission, TX for resistance evaluation. In order to be evaluated for organophosphate resistance the tick must lay eggs, those eggs hatch, and produce a sufficient number of tick larvae for bioassay. This process can take weeks to perform. The current work describes a method for the extraction of acetylcholinesterase, the target of organophosphates, from the brain of a single adult tick. With the extracted AChE, a rapid enzyme inhibition assay can be performed to diagnose insensitive AChE that is a diagnostic characteristic of an organophosphate resistant tick. This assay can be completed the same day, as the tick is collected, saving considerable time in the management of resistance.
Technical Abstract: A sonication method for extraction of acetylcholinesterase (AChE) from the synganglion of an adult tick is described. The method provides for the extraction of sufficient AChE for multiple assays of enzyme activity in the presence of specific inhibitors for the rapid diagnosis of organophosphate (OP) insensitivity. A single synganglion from adult ticks of either gender and various stages of feeding can successfully be used for AChE extraction. The method should find utility in support of the Cattle Fever Tick Surveillance and Quarantine Program maintained by USDA-APHIS/Veterinary Services along the south Texas border that prevents reentry of Boophilus spp. into the United States from endemic populations in Mexico.