Bovine anaplasmosis is the most prevalent tick-transmitted disease of cattle worldwide and a major obstacle to profitable beef production. Use of chlortetracycline-medicated feed to control active anaplasmosis infections during the vector season has raised concerns about the potential emergence of antimicrobial resistance in bacteria that may pose a risk to human health. Furthermore, the absence of effectiveness data for a commercially available, conditionally licensed anaplasmosis vaccine is a major impediment to implementing anaplasmosis control programs. The primary objective of this study was to develop a single-dose vaccine delivery platform to produce long-lasting protective immunity against anaplasmosis infections. Twelve Holstein steers, aged 11-12 weeks, were administered a novel 3-stage, single-dose vaccine against Anaplasma marginale (Am) major surface protein 1a. The vaccine consisted of a soluble vaccine administered subcutaneously (s.c.) for immune priming, a vaccine depot of a biodegradable polyanhydride rod with intermediate slow release of the vaccine for boosting immune response, and an immune-isolated vaccine platform for extended antigen release (VPEAR implant) deposited s.c. in the ear. Six calves were randomly assigned to two vaccine constructs (n=3) that featured rods and implants containing a combination of two different adjuvants, diethylaminoethyl (DEAE)-Dextran and Quil-A (Group A). The remaining 6 calves were randomly assigned to two vaccine constructs (n=3) that featured rods and implants containing the same adjuvant (either DEAE-Dextran or Quil A) (Group B). Twenty one months post-implantation, calves were challenged intravenously with Am stabilate and were monitored weekly for signs of fever, decreased packed cell volume (PCV) and bacteremia. Data were analyzed using a mixed effects model and chi-squared tests (SAS v9.04.01, SAS Institute, Cary, NC). Calves in Group A had higher PCV than calves in Group B (P = 0.006) at day 35 post-infection. Calves in Group A were less likely to require antibiotic intervention compared with calves in Group B (P = 0.014). Results indicate that calves exhibited diminished clinical signs of anaplasmosis when antigen was delivered with a combination of adjuvants as opposed to a single adjuvant. This demonstrates the feasibility of providing long lasting protection against clinical bovine anaplasmosis infections using a subcutaneous ear implant vaccine construct.This is a pre-copyedited, author-produced version of an article accepted for publication in Journal of Animal Science. The version of record: Curtis, Andrew K., Kathryn E. Reif, Michael D. Kleinhenz, Miriam S. Martin, Brandt Skinner, Sean M. Kelly, Douglas E. Jones, Emily J. Reppert, Shawnee R. Montgomery, Balaji Narasimhan, Tippawan Anantatat, Majid Jaberi-Douraki, and Johann F. Coetzee. "Development of a subcutaneous ear implant to deliver an anaplasmosis vaccine to dairy steers." Journal of Animal Science (2019) is available online at DOI: 10.1093/jas/skz392. Posted with permission.</p
