Cloning, expression and evaluation of the efficacy of a recombinant Haemaphysalis concinna Hc-23 antigen in rabbits

Haemaphysalis concinna is wide spread in China, and negatively impacted on husbandry production and then resulted in severe economic losses. Methods available for the control of ticks are mainly based on chemotherapy. However, this approach is associated with a number of disadvantages; searching for alternative tick control measures is necessary and vaccination is one of the best control strategies. Through H. concinna Hc-23 gene PCR amplification, cloning and sequencing, sequence analysis showed that Hc-23 genes could be amplified in nymphal, larvae and adult ticks. BLAST analysis suggested that Hc-23 gene was 99.83% homology with P27/30 of Chinese strains H. longicornis, and 99.67% with Japanese strains, but 88.06% with Rhipicephalus tick troponin I gene. The recombinant Hc23 expressed in BL21(DE3) with Freund's complete adjuvant (FCA) was used to immunize 6 rabbits, then another 6 were immunized with PBS and 6 with control FCA (as control) were challenge-infested with ticks at different developmental stages of the same specie. The result showed that ticks that fed on rHc23-immunized rabbits were observed to feed longer compared to the control (P ≤ 0.05), the engorged body weights of ticks feeding on rHc23-immunized rabbits were lighter than the control (P ≤ 0.05), and an apparent reduction in laying amount was observed for adult ticks fed on rHc23-immunized rabbits (P ≤ 0.05). These results demonstrated that the Hc-23 protein might be a useful vaccine candidate antigen for biological control of ticks.