Immunoprotective Evaluation of Scoloptoxin SSD14, Inositol Monophosphatase, and Neprilysin Against Ticks Infestation

Ticks are hematophagous arthropods and potential vectors of numerous tick-borne pathogens affecting both animals and humans. Globally, synthetic acaricides remains primary strategy for controlling tick infestations, however their prolong use poses challenges including resistance development and environmental contaminations. Herein, three candidate antigens including scoloptoxin SSD14, inositol monophosphatase and neprilysin antigens were immunologically characterized as anti-tick vaccine. Using In-silico bioinformatics tools, these Rhipicephalus microplus proteins were selected as a vaccine candidates based on physiochemical analyses and epitope prediction. The DNA fragments encoding these proteins were cloned into pET-32a(+) expression vectors, transformed into Escherichia coli BL-21 star for recombinant protein expression. Rabbits were subcutaneously immunized using 100 µg of each purified protein emulsified in oil adjuvant, and the control group received only adjuvant. The bioinformatic analyses of these proteins revealed the presence of several immunogenic epitopes which could be useful in a vaccine against ticks. Biological parameters including weight and number of fully engorged female ticks, egg laying, egg fertility, nymphal molting rate, and antibody level were statistically analyzed using Student t-test and one-way ANOVA. In vivo assessment demonstrated that all three antigens reduced tick parameters, the scoloptoxin SSD14 statistically decreased adult female egg laying up to 16%, and egg fertility decreased by 37%, with an overall vaccine efficacy of 47%. Inositol monophosphatase statistically reduced the number of adult females up to 23%, egg laying in adult females up to 11%, and larval hatching decreased by 40%, accounting for 59% total vaccine efficacy. Neprilysin statistically reduced the nymph numbers to 40%, larval hatching up to 41%, with overall vaccine efficacy of 64%. These findings highlight the potential of these antigens in the development of anti-tick vaccine.