Partial characterization of the voltage-gated sodium channel gene and molecular detection of permethrin resistance in Rhipicephalus annulatus (Say, 1821)

Authors: KLAFKE, GUILHERME - Non ARS Employee; MORENO, HANNAH - University Of Texas Rio Grande Valley; Tidwell, Jason; Miller, Robert; Thomas, Donald; FERIA-ARROYO, TERESA - University Of Texas Rio Grande Valley; Perez De Leon, Adalberto - Beto

Submitted to: Ticks and Tick Borne Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2019
Publication Date: 5/1/2020
Citation: Klafke, G.M., Moreno, H.C., Tidwell, J.P., Miller, R., Thomas, D.B., Feria-Arroyo, T.P., Perez De Leon, A.A. 2020. Partial characterization of the voltage-gated sodium channel gene and molecular detection of permethrin resistance in Rhipicephalus annulatus (Say, 1821). Ticks and Tick Borne Diseases. https://doi.org/10.1016/j.ttbdis.2019.101368.
DOI: https://doi.org/10.1016/j.ttbdis.2019.101368

Interpretive Summary: The cattle tick, Rhipicephalus annulatus, remains a threat to the national livestock industry after it was eradicated from the U.S. because it is established in Mexico. In addition to direct effects on livestock health due to its obligate blood feeding habit, R. annulatus is also a vector of the microbes causing bovine babesiosis and anaplasmosis, which can kill cattle. Acaricides are chemical substances used to kill ticks. However, ticks can become resistant to acaricides through processes mediated by genetic changes. We report here results of an investigation on cattle ticks causing an outbreak in the U.S. that showed low level of resistance to the pyrethroid acaricide permethrin. A novel molecular assay was adapted to screen for pyrethroid resistance in R. annulatus. Pyrethroids target the voltage-gated sodium channel in the nervous system of ticks. This effort involved the partial characterization of the gene coding for the voltage-gated sodium channel. Our results represent the first case of pyrethroid resistance in R. annulatus collected in the U.S.

Technical Abstract: The cattle tick, Rhipicephalus annulatus (Say) is a vector of bovine babesiosis and responsible for direct and indirect losses to cattle producing areas located in temperate and subtropical dry regions. Resistance against pyrethroids has been reported for this species in Asia and Africa, but never before in North America. An outbreak strain, Rio Lado, collected close to the border between Mexico and the United States, in Maverick County, Texas, showed low level of resistance to permethrin, a pyrethroid pesticide. We used genomic material from different strains of cattle ticks collected within the Permanent Quarantine Zone (Rio Lado, Vega and Klein Grass strains) to partially characterize the coding gene of the voltage-gated sodium channel (Na-channel), target-site of pyrethroid pesticides, and search for putative mutations associated with resistance using quantitative PCR high resolution melt (HRM) analysis. The two amplified fragments, corresponding to domains II and III of the Na-channel, were 100% identical to its ortholog in Rhipicephalus microplus (Canestrini). No nucleotide polymorphisms in the Na-channel gene were observed in the pyrethroid-resistant Rio Lado strain, when compared to the susceptible strains Klein Grass and Vega. This study reports the first case of pyrethroid resistance in R. annulatus collected in the United States. Also, we provide new genomic data for this species of tick that allows for the development of a new method to screen for mutations associated with pyrethroid resistance.