Rhipicephalus microplus economically impacts cattle production in tropical and subtropical countries. Application of acaricides constitutes the major control method; however, inadequate use has increased resistant tick populations, resulting in environmental and cattle product contamination. Anti-tick vaccines based on the Bm86 antigen are an environmentally friendly, safe, and economically sustainable alternative for controlling R. microplus infestations. Nevertheless, variable efficacy has been experienced against different geographic tick strains. Herein, we evaluated the efficacy of a conserved polypeptide Bm86 derived from a Mexican R. microplus strain previously characterized. Twelve cows were assigned to three experimental groups and immunized with three doses of the polypeptide Bm86 (pBm86), adjuvant/saline alone, and Bm86 antigen (control +), respectively. Specific IgG antibody levels were measured by ELISA and confirmed by Western blot. In addition, the reproductive performance of naturally infested R. microplus was also determined. The more affected parameter was the adult female tick number, with a reduction of 44% by the pBm86 compared to the controls (p < 0.05), showing a vaccine efficacy of 58%. Anti-pBm86 IgG antibodies were immunogenic and capable of recognizing the native Bm86 protein in the eggs, larvae, and guts of R. microplus. The negative correlation between antibody levels and the reduction of naturally tick-infested cattle suggested that the effect of the polypeptide Bm86 was attributed to the antibody response in immunized cattle. In conclusion, the polypeptide Bm86 showed a specific immune response in cattle and conferred protection against R. microplus in a Mexican tropical region. These findings support further experiments with this antigen to demonstrate its effectiveness as a regional vaccine.

Uno de los principales problemas sanitarios de la ganadería bovina son las infestaciones ocasionadas por garrapatas. La especie más importante es Rhipicephalus microplus, la cual afecta al 80% de la población bovina del mundo. Su control se basa principalmente en el uso de ixodicidas, sin embargo, el uso excesivo e inadecuado ha generado cepas de garrapatas multiresistentes. Alternativamente, se ha propuesto al control inmunológico como un método importante para reducir las poblaciones de garrapatas, siendo la vacuna recombinante de Bm86 la única disponible comercialmente y con reportes de variaciones en su eficacia debido a la presencia de polimorfismos en el gen codificador. El objetivo de este trabajo fue caracterizar una región inmunogénica de la proteína Bm86 de R. microplus cepa “Media Joya” con el fin de proponer un candidato vacunal que sea conservado y con mínima variabilidad en cuanto a su eficacia. Se utilizaron herramientas computacionales, técnicas de biología molecular y análisis filogenéticos, y se obtuvo una región inmunogénica constituida por 178 aminoácidos y con 98–100% de identidad y similitud con respecto a cepas de garrapatas R. microplus provenientes del continente americano. Adicionalmente, se requiere evaluar el potencial inmunoprotector de la región de Bm86 caracterizada en este trabajo como vacuna anti-garrapatas.

The objective of this study was to evaluate essential oils (EOs) as an alternative control method for Rhipicephalus microplus and Amblyomma mixtum larvae. The EOs used were obtained by steam distillation from the leaves of cinnamon (Cinnamomum verum), mexican mint (Plectranthus amboinicus), lemongrass (Cymbopogon citratus), peppercorns (Pimenta dioica), and peruvian pepper tree (Schinus molle). To evaluate the acaricidal effect of EOs against the larvae of two tick species, a larval immersion test (LIT) was performed using six concentrations (10 mg/mL, 5 mg/mL, 2.5 mg/mL, 1.87 mg/mL, 1.25 mg/mL, and 0.6 mg/mL), in addition to a negative control group (water + ethanol) and three positive controls (organophosphate, formamidine, and pyrethroid). LIT results were obtained 48 h after exposure. Data were processed using Probit procedure to determine the lethal concentrations at 50% (LC₅₀), 95% (LC₉₅), and 99% (LC₉₉). For R. microplus, 99% mortality was obtained at concentrations as low as 1.4 mg/mL for S. molle, while the highest LC₉₉ was recorded with P. dioica at 23 mg/mL. In the case of A. mixtum, higher concentrations were required to achieve a high mortality rate. EO of P. amboinicus had the lowest acaricidal effect, requiring 26.2 mg/mL to achieve an LC₉₉, while S. molle required a concentration of 6.9 mg/mL to achieve an LC₉₉.