Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/30/2010
Publication Date: 10/30/2010
Citation: Waters, W.R., Palmer, M.V., Thacker, T.C. 2010. Bovine Tuberculosis Vaccine Efficacy Studies: Neonatal Calves and White-tailed Deer [abstract]. American College of Veterinary Pathologists/American Society for Veterinary Clinical Pathology. p. 89.
Technical Abstract: Introduction Tuberculosis (TB) in humans and animals may result from exposure to bacilli within the Mycobacterium tuberculosis complex (i.e., M. tuberculosis, M. bovis, M. africanum, M. pinnipedi, M. microti, M. caprae, or M. canetti)(#1). Mycobacterium bovis is the species most often isolated from tuberculous cattle. Unlike M. tuberculosis, M. bovis has a wide host range, including several wildlife maintenance hosts (#2). While the mainstay of bovine TB control has been abattoir inspection plus targeted test / cull campaigns, vaccines are now being considered as an additional tool for control, both in cattle and wildlife (#3-4). The first known tuberculosis (TB) vaccine purposefully administered to cattle was M. bovis bacillus Calmette Guerin (BCG), circa 1911 (#5). The efficacy of BCG varies under both experimental and field conditions (#6); thus, other vaccine approaches have been evaluated (#7). An attenuated live vaccine with more consistent efficacy and/or improved safety as compared to BCG should prove invaluable as a bovine TB vaccine, either alone or in combination with subunit vaccines (#8-10). Within the United States (i.e., northeast Michigan), free-ranging white-tailed deer are a wildlife reservoir of M. bovis (#11-14), presumably transmitting the disease to at least 44 cattle herds on 39 different farms. Control efforts such as limiting wildlife baiting / feeding practices and increased deer hunting have resulted in a reduced apparent prevalence of TB in deer (#15). However, there is increasing public resentment of ongoing control measures and targeted vaccination is an appealing option, particularly as a means to limit transmission from deer to cattle. Our long-term goal is to develop a live attenuated DIVA (differentiate infected from vaccinated animals) vaccine with improved efficacy and safety as compared to BCG for use in cattle and associated wildlife hosts. Currently, ESAT-6 and CFP-10 are leading candidates for use as antigens in modern bovine TB diagnostic assays. ESAT-6 and CFP-10 are encoded in the RD1 region of the genomes of tuberculous mycobacteria and deletion of RD1 is the primary attenuating defect of BCG (#16). Thus, a Delta RD1 vaccine is a logical selection for evaluation. Our approach is two-fold: (A) characterize the safety and efficacy of BCG in white-tailed deer to expedite field application as this vaccine has a long track record of use in many species and (B) evaluate new generation TB vaccines (i.e., Delta RD1 mutants) in calves, as a model for use in humans and potentially for use in calves or other wildlife hosts of M. bovis. Aerosol Challenge Model of Infection in neonatal calves With our protocol, vaccines are administered to calves at ~2 wks of age and virulent M. bovis delivered via aerosol at ~3.5 months of age 17-19. The challenge inoculum is delivered to restrained calves by nebulization of ~10**3 cfu M. bovis strain 95-1315 in PBS into a mask (Trudell Medical International, London, ON, Canada) covering the nostrils and mouth. Upon inspiration, inoculum is inhaled through a one-way valve into the mask and directly into the lungs via the nostrils. The process continues until the inoculum, a 1 ml PBS wash of the inoculum tube, and an additional 2 ml PBS are delivered, a process taking ~10 min. Strict BL-3 safety protocols are followed to protect personnel from exposure to M. bovis. Variables used to evaluate vaccine efficacy include: gross pathology, radiograph morphometry, histopathology, mycobacterial culture (quantitative and qualitative), and various immune parameters (#18-19). An initial study was performed to compare the efficacy of BCG (originally attenuated circa 1913 by continued passage of a Nocard strain of M. bovis on potato slices / ox bile / glycerin media) to M. bovis Ravenel Delta RD1 (#18). Key findings from this calf vaccine trial were: (A) vaccination of neo