Abstract
Abstract Bovine anaplasmosis is the most prevalent tick-transmitted disease of cattle worldwide and a major obstacle to beef production. The objective of the study was to test the ability of a single-dose delivery platform to produce long-lasting immunity against anaplasmosis infections. Twelve Holstein steers were administered a 3-stage, single-dose vaccine against Anaplasma marginale major surface protein 1a. The vaccine consisted of a soluble vaccine administered subcutaneously for immune priming, a biodegradable polyanhydride depot for intermediate slow-release of the vaccine for boosting the immune response, and an immune-isolated vaccine platform for extended antigen release deposited subcutaneously in the ear. Six calves were randomly assigned to two vaccine constructs that featured rods and implants containing a combination of two adjuvants (DEAE-Dextran and Quil-A). The remaining 6 calves were randomly assigned to two vaccine constructs that featured rods and implants containing the same adjuvant (DEAE-Dextran or Quil-A). Twenty months post-implantation, calves were challenged with Anaplasma marginale stabilate and were monitored weekly for signs of fever, decreased packed cell volume (PCV) and bacteremia. Outcome variables (fever, PCV, bacteremia) were analyzed using a linear mixed model (PROC GLMMIX; SAS University Edition v9.04.01, SAS Institute, Cary, NC). Two-tailed chi-squared tests were used to compare need for antibiotic intervention between vaccine constructs. Calves within the combination adjuvant construct group (DEAE-D and Quil-A) exhibited significantly (P = .006) higher PCV than calves within the single adjuvant construct group (DEAE-Dextran or Quil-A). Likewise, calves within the combination adjuvant group required significantly (P = .014) fewer antibiotic interventions compared with calves in the single adjuvant group. Findings of this study suggest that calves exhibited significantly diminished clinical signs of anaplasmosis when vaccine was delivered with a combination of adjuvants as opposed to a single adjuvant in a single-dose delivery platform.
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