Intestinal changes and performance parameters in ticks feeding on calves immunized with subunits of immunogens against Rhipicephalus microplus
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We describe the intestinal changes and biological parameters of the tick species Rhipicephalus microplus exposed to the immune response of calves vaccinated with two subunits of immunogens. The first group of Bos taurus calves was immunized with a synthetic peptide (SBm7462), whereas the second group received an inoculum for synthetic control. The third group was immunized with a recombinant peptide (rSBm7462); an inoculum was injected into a fourth group of calves for recombinant control. Each formulation was administered to these calves during three times at intervals of 30 days. At 21 days after the last immunization, the calves were challenged using a total of 4500 larvae per animal. Indirect ELISA was realized to identify the kinetics of IgGs from samples of calves studied. Naturally detaching ticks were collected for analyses of biological performance and histological changes in the midgut. We dissected randomly detached ticks. The midgut of each of these ticks was removed and processed routinely for histology, stained with hematoxylin-eosin (H&E) and slow Giemsa. Slides were also subjected to immunohistochemistry. The antibody response showed significant induction of high-affinity IgGs in calves immunized with both peptides in comparison to calves of the control groups. Histological changes included damage of the intestinal epithelium in ticks fed on immunized hosts and intense immunostaining in midgut cells, using the serum of calves immunized with recombinant peptide. There were significant differences in all biological performing parameters of ticks detached from vaccinated calves in comparison with ticks of the control groups. We identified reductions of 87.7 and 93.5% in engorged ticks detached from calves immunized with a synthetic and recombinant peptides, respectively, a 28 and 8.60% lower egg mass in groups immunized with synthetic and recombinant peptides, respectively, and a 38.4% reduction of the value of nutrient index/tick in the group immunized with the recombinant peptide. Our findings show that the immune response induced by small peptides in cattle can modify the digestion and metabolism of ticks fed on vaccinated animals, resulting in changes in tick performance.
KeywordsIxodidae Cattle tick Tick control Immunogen Tick proteins Midgut Histology
The authors gratefully acknowledge FAPEMIG (Foundation for Research Support of the State of Minas Gerais, Brazil) (Grant No. APQ-00998-12) for providing financial support and CAPES (Coordination for The Improvement of Higher Education Personnel) for providing scholarships to graduate students.
Compliance with ethical standards
Conflict of interest
There are no competing interests that may influence the results of this study.
The ticks were collected from cattle without causing pain or distress. The calves used in this trial received handling and treatment under qualified veterinary supervision in accordance with the animal experimentation rules described in the International Guiding Principles for Biomedical Research Involving Animals. This study and the research proposal were approved by the Animal Research Ethics Committee of the EMBRAPA: CEUA-EGL 06/2013.
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