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Title: Acaricide and Ivermectin resistance in a field population of Rhipicephalus microplus (Acari: Ixodidae) collected from Red Deer (Cervus elaphus) in the Mexican Tropics

Author
item RODRIGUEZ-VIVAS, ROGER - Autonomous University Of Yucatan
item Miller, Robert
item OJEDA-CHI, M - Autonomous University Of Yucatan
item ROSADO-AGUILAR, J - Autonomous University Of Yucatan
item TRINIDAD-MARTINEZ, I - Autonomous University Of Yucatan
item Perez De Leon, Adalberto - Beto

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2013
Publication Date: 2/24/2014
Citation: Rodriguez-Vivas, R.I., Miller, R., Ojeda-Chi, M.M., Rosado-Aguilar, J.A., Trinidad-Martinez, I.C., Perez De Leon, A.A. 2014. Acaricide and Ivermectin resistance in a field population of Rhipicephalus microplus (Acari: Ixodidae) collected from Red Deer (Cervus elaphus) in the Mexican Tropics. Veterinary Parasitology. 200(1-2):179-188.

Interpretive Summary: Red deer are an alternative host for the cattle fever tick Rhipicephalus microplus. The cattle fever tick is a bloodfeeding pest of cattle throughout the tropical and sub-tropical regions of the world. These ticks lower cattle production potential directly through reduced weight gain due to blood loss from feeding, and indirectly through the transmission of disease-causing infectious agents this tick carries. In this study we determined that a cattle fever tick strain collected from red deer in a topical region of Mexico were resistant to many different classes of chemicals, or acaricides, making it very difficult to control this tick on these animals. This publication illustrates the ability for the development of acaricide resistance in ticks infesting treated deer. In comparison to efforts by the Cattle Fever Tick Eradication Program that include a campaign to control tick infestations in white-tailed deer using different acaricides, our findings highlight the risk of tick control on deer to drive acaricide resistance in cattle fever tick populations causing outbreaks in the U.S. Ticks collected from deer in areas where acaricides are used to control cattle fever ticks infesting livestock should be monitored for resistance.

Technical Abstract: Red deer (Cervus elaphus), taurine (Bos taurus) and zebuine (Bos indicus) breeds of cattle and their crosses, and the southern cattle fever tick (Rhipicephalus microplus) are non-native species that were introduced to Mexico through the livestock trade. Red deer raised in the Neotropics can die from heavy Rhipicephalus (Boophilus) microplus infestations. The control of tick infestations in red deer and cattle is achieved primarily through the use of acaricidal products, including those containing macrocyclic lactones like ivermectin as the active ingredient. However, the indiscriminate use of acaricidal products results in a strong selection for acaricide resistance among populations of R. microplus. In Mexico, resistance to one or multiple classes of acaricides has been reported in R. microplus infesting cattle, but information on acaricide susceptibility in R. microplus infesting red deer is lacking. Results from the research reported here revealed various levels of resistance to different classes of acaricides in R. microplus collected from red deer in the Mexican tropics. Emphasis was placed on the susceptibility to ivermectin due to its extensive use by producers in the region. Engorged R. microplus females were collected from a red deer farm in Yucatan, Mexico. The larval packet test (LPT) was used to detect resistance to the organophosphates (OPs) chlorpyrifos and coumaphos, pyrethroids (SPs) cypermethrin and flumethrin, and the phenylpyrazol, fipronil. Resistance to the formamidine amitraz, and ivermectin was ascertained using the larval immersion test (LIT). Mortality data were subjected to probit analysis to determine lethal concentrations and resistance ratios to kill 50% (RR50) and 99% (RR99) of the tick population under evaluation in relation to susceptible reference strains. Additionally, allele specific polymerase chain reaction was used to detect the sodium channel F1550I mutation associated with SP resistance in R. microplus. The R. microplus Yucatan population showed very high resistance to the two SPs evaluated (RRs >72.2 for cypermethrin; RR for permethrin resistance was so high a dose-response curve could not be produced). All individual larvae tested to detect the sodium channel F1550I mutation associated with SP resistance in R. microplus were homozygous. R. microplus infesting red deer in Yucatan showed different levels of resistance to OPs (chlorpyrifos: RR50=1.55, RR99= 0.63; coumaphos: RR50=6.8, RR99= 5.9; fipronil: RR50=1.8, RR99= 0.9; and amitraz: RR50=2.3, RR99= 4.4). Resistance to ivermectin was regarded as moderate (RR50=7.1, RR99= 4.9). We report for the first time a R. microplus population collected from red deer in Mexico with different levels of resistance to OPs, SPs, Am, fipronil, and ivermectin. The implications of the various levels of resistance reported here are discussed in the context of efforts for sustainable control of R. microplus in the Mexican tropics where diversified livestock production is practiced. In comparison to efforts by the Cattle Fever Tick Eradication Program that include a campaign to control tick infestations in white-tailed deer using different acaricides, our findings highlight the risk of tick control on deer to drive acaricide resistance in cattle fever tick populations causing outbreaks in the U.S. Ticks collected from deer in areas where acaricides are used to control cattle fever ticks infesting livestock should be monitored for resistance.