In silico selection and in vivo evaluation of scoloptoxin SSD14, Rm-inositol monophosphatase, and Rm-neprilysin as potential anti-tick vaccines

Ticks are parasitic arthropods, responsible for vectoring tick-borne pathogens to animals and humans. Globally, synthetic acaricides are used to control tick infestations; however, alternative controls methods are in development. In this study, Rhipicephalus microplus (Rm)-scoloptoxin SSD14 (Rm-SSD), Rm-inositol monophosphatase (Rm-IMP), and Rm-neprilysin (Rm-Nep) proteins were characterized as anti-tick vaccine candidates. Based on physicochemical analyses, immunological and epitope prediction these three Rhipicephalus microplus proteins were selected as vaccine candidates against Rhipicephalus linnaei tick model infestation. The recombinant proteins were expressed in Escherichia coli system followed by purification using chromatography. The vaccination challenge was conducted using New Zeeland white rabbits divided into four groups (n = 4 per group): a PBS control group and three experimental groups immunized with the Rm-SSD, Rm-IMP or Rm-Nep emulsified in oil-based adjuvant. After immunization, rabbits were experimentally infested with adult and nymphal stages of R. linnaei. Following vaccination, Rm-SSD significantly reduced adult female egg laying by up to 15.96% and egg fertility by 37.45%, resulting in an overall vaccine efficacy of 47.47%. Rm-IMP significantly reduced the number of adult females by up to 22.95%, egg laying by up to 10.82%, and larval hatching by 39.91%, accounting for a total vaccine efficacy of 58.72%. Rm-Nep significantly reduced nymph numbers by 39.22% and larval hatching by up to 41.11%, with an overall vaccine efficacy of 64.20%.The results of the current study justify the use of these proteins in future as cocktail vaccine against R. microplus infesting field grazing bovines. Such strategy contributes to offering a more robust and sustainable approach for tick control under diverse climatic conditions.