Abstract
BackgroundTicks represent a significant health risk to animals and humans due to the variety of pathogens they can transmit during feeding. The traditional use of chemicals to control ticks has serious drawbacks, including the selection of acaricide-resistant ticks and environmental contamination with chemical residues. Vaccination with the tick midgut antigen BM86 was shown to be a good alternative for cattle tick control. However, results vary considerably between tick species and geographic location. Therefore, new antigens are required for the development of vaccines controlling both tick infestations and pathogen infection/transmission. Tick proteins involved in tick-pathogen interactions may provide good candidate protective antigens for these vaccines, but appropriate screening procedures are needed to select the best candidates.MethodsIn this study, we selected proteins involved in tick-Anaplasma (Subolesin and SILK) and tick-Babesia (TROSPA) interactions and used in vitro capillary feeding to characterize their potential as antigens for the control of cattle tick infestations and infection with Anaplasma marginale and Babesia bigemina. Purified rabbit polyclonal antibodies were generated against recombinant SUB, SILK and TROSPA and added to uninfected or infected bovine blood to capillary-feed female Rhipicephalus (Boophilus) microplus ticks. Tick weight, oviposition and pathogen DNA levels were determined in treated and control ticks.ResultsThe specificity of purified rabbit polyclonal antibodies against tick recombinant proteins was confirmed by Western blot and against native proteins in tick cell lines and tick tissues using immunofluorescence. Capillary-fed ticks ingested antibodies added to the blood meal and the effect of these antibodies on tick weight and oviposition was shown. However, no effect was observed on pathogen DNA levels.ConclusionsThese results highlighted the advantages and some of the disadvantages of in vitro tick capillary feeding for the characterization of candidate tick protective antigens. While an effect on tick weight and oviposition was observed, the effect on pathogen levels was not evident probably due to high tick-to-tick variations among other factors. Nevertheless, these results together with previous results of RNA interference functional studies suggest that these proteins are good candidate vaccine antigens for the control of R. microplus infestations and infection with A. marginale and B. bigemina.
Highlights
Ticks represent a significant health risk to animals and humans due to the variety of pathogens they can transmit during feeding
Production and characterization of antibodies against tick proteins involved in tick-pathogen interactions Proteins involved in tick-A. marginale (Subolesin (SUB), SILK) and tick-B. bigemina (TROSPA) interactions as determined by systems biology and RNA interference (RNAi) functional studies were selected to characterize their potential as antigens for the control of both R. microplus tick infestations and infection with A. marginale or B. bigemina
Previous results suggested a role for SILK in tick-host and tick-pathogen interactions, these results were only partially confirmed here. The hypothesis behind this experimental approach for the selection of candidate tick protective antigens is that antibodies mediate the main protective mechanism for tick vaccines, something that has been demonstrated for several antigens such as BM86, SUB, SILK and TROSPA for which a direct correlation exists between antibody titers in vaccinated animals and vaccine efficacy [25,35,46,47,48]
Summary
Ticks represent a significant health risk to animals and humans due to the variety of pathogens they can transmit during feeding. Chemical acaricides are currently the main method for the control of tick infestations, but problems associated with their use, such as limited efficacy in some regions due to selection of acaricide-resistant ticks and contamination of the environment and animal products with chemical residues, indicate the need for alternative control methods [4]. Vaccination with commercial vaccines containing the recombinant Rhipicephalus (Boophilus) microplus BM86 gut antigen demonstrated their advantages for tick control, including cost-effectiveness and reduction in acaricide application These vaccines reduced the prevalence of anaplasmosis and babesiosis in some regions, presumably through reducing exposure of cattle to infected ticks [6]. New antigens are required for the development of vaccines affecting tick feeding, reproduction and vector capacity to control both tick infestations and pathogen infection/transmission
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