Humoral immune response of dairy cattle immunized with rBm95 (KU-VAC1) derived from Thai Rhipicephalus microplus.

Rhipicephalus (Boophilus) microplus is an important cause of economic losses in Thailand through direct effects of feeding on cattle and pathogen transmission. Current tick control methods rely on expensive chemical acaricides that result in environmental contamination, residues in food animal products and acaricide-resistant ticks. Anti-tick vaccines based on concealed antigens have shown promising results in the control of cattle tick. Thus, recombinant Bm95 (rBm95) from Thai R. microplus (KU-VAC1) was cloned and expressed to test as an anti-tick vaccine in Thailand. The objective of this study was to compare antibody responses induced by KU-VAC1 to that obtained after vaccination with Gavac that is based on the Bm86 homologue. Four groups of six cattle each were immunized with KU-VAC1, Gavac, adjuvant or phosphate-buffered saline, and boosted three times at 21-day intervals. Enzyme-linked-immunosorbent serologic assay were used to measure the humoral antibody responses specific to Thai rBm95. Cattle immunized with either KU-VAC1 or Gavac showed significantly greater antibody production than the controls. Antibody titres were detected after the first immunization and peaked after the seventh week. These results indicated that KU-VAC1 and Gavac are similarly immunogenic, and that further studies are warranted to compare performance parameters of ticks fed on immunized cattle.

Immunization of rabbits with recombinant serine protease inhibitor reduces the performance of adult female Rhipicephalus microplus.

Molecules secreted from the tick salivary gland modulate the vertebrate host immune response, thus representing potential targets for novel tick control measures. Tick salivary gland serine protease inhibitor (Serpin) is one such molecule that may facilitate tick feeding, blood meal digestion and pathogen transmission. The objective of this study was to determine the immunogenicity and protection of recombinant Rhipicephalus (Boophilus) microplus salivary gland Serpin (rSerpin) in rabbits. Rabbits were injected with rSerpin, adjuvant or phosphate-buffered saline (PBS) alone, and challenge infested with 500 R. microplus larvae that were allowed to continuously feed and moult through the adult stage. All immunized rabbits generated antibodies to rSerpin in the second week after immunization. Ticks fed on immunized rabbits resulted in 83% reduction in adult engorgement and 34% reduction in egg mass weight compared with the PBS control. These results indicated that this tick Serpin is immunogenic to rabbits, and suggested that this vaccine candidate antigen can confer protective immunity against cattle ticks in this experimental model.