Abstract
BackgroundDespite the use of chemical acaricides, tick infestations continue to affect animal health and production worldwide. Tick vaccines have been proposed as a cost-effective and environmentally friendly alternative for tick control. Vaccination with the candidate tick protective antigen, Subolesin (SUB), has been shown experimentally to be effective in controlling vector infestations and pathogen infection. Furthermore, Escherichia coli membranes containing the chimeric antigen composed of SUB fused to Anaplasma marginale Major Surface Protein 1a (MSP1a) (SUB-MSP1a) were produced using a simple low-cost process and proved to be effective for the control of cattle tick, Rhipicephalus (Boophilus) microplus and R. annulatus infestations in pen trials. In this research, field trials were conducted to characterize the effect of vaccination with SUB-MSP1a on tick infestations and the prevalence of tick-borne pathogens in a randomized controlled prospective study.MethodsTwo cattle and two sheep farms with similar geographical locations and production characteristics were randomly assigned to control and vaccinated groups. Ticks were collected, counted, weighed and classified and the prevalence of tick-borne pathogens at the DNA and serological levels were followed for one year prior to and 9 months after vaccination.ResultsBoth cattle and sheep developed antibodies against SUB in response to vaccination. The main effect of the vaccine in cattle was the 8-fold reduction in the percent of infested animals while vaccination in sheep reduced tick infestations by 63%. Female tick weight was 32-55% lower in ticks collected from both vaccinated cattle and sheep when compared to controls. The seroprevalence of Babesia bigemina was lower by 30% in vaccinated cattle, suggesting a possible role for the vaccine in decreasing the prevalence of this tick-borne pathogen. The effect of the vaccine in reducing the frequency of one A. marginale msp4 genotype probably reflected the reduction in the prevalence of a tick-transmitted strain as a result of the reduction in the percent of tick-infested cattle.ConclusionsThese data provide evidence of the dual effect of a SUB-based vaccine for controlling tick infestations and pathogen infection/transmission and provide additional support for the use of the SUB-MSP1a vaccine for tick control in cattle and sheep.
Highlights
Despite the use of chemical acaricides, tick infestations continue to affect animal health and production worldwide
These results suggested differences between cattle and sheep that could be explained by different factors such as higher tick infestations in cattle when compared to sheep (Figure 3A and B) that require more time for the vaccine to reduce tick infestations, differences in tick species infesting cattle and sheep and/or other factors
The percent of infested sheep was not affected by vaccination with SUB-Major Surface Protein 1a (MSP1a) (Figure 7B-D). These results showed that the main effect of the SUB-MSP1a vaccine in cattle was the reduction in the percent of infested animals but not in the tick infestation rate of these animals
Summary
Despite the use of chemical acaricides, tick infestations continue to affect animal health and production worldwide. Acaricides are a major component of integrated tick control strategies, but their application has had limited efficacy in reducing tick infestations and is often accompanied by serious drawbacks, including the selection of acaricide-resistant ticks, environmental contamination and contamination of milk and meat products with drug residues [4]. All of these issues reinforce the need for alternative approaches to control tick infestations and pathogen transmission, including the use of vaccines with tick antigens [5,6,7]. BM86-based vaccines have limited efficacy against other tick species and new vaccines are needed for the control of multiple tick species infestations, which occur in many areas used for animal husbandry [5,6,8]
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