• Vaccine Name: B. abortus strain 45/20
• Target Pathogen: Brucella spp.
• Target Disease: Brucellosis
• Vaccine Ontology ID: VO_0000723
• Type: attenuated live vaccine
• Antigen: Whole Brucella organism
• Preparation: The 45/20 strain was isolated from guinea pigs in 1938 (Moriyon et al., 2004).
• Virulence: The original strain of 45/20 was known to revert to smooth pathogenic forms when injected into cattle. Due to this instability, the vaccine is not currently marketed (Moriyon et al., 2004).
  
• Description: B. abortus strain 45/20 is a rough form of the bacterium that can confer immunity (Moriyon et al., 2004).

Sheep Response

• Vaccination Protocol: 15 lambs were vaccinated with 45/20 bacterin, and a control group remained unvaccinated. Revaccinations were performed 18 weeks later. At regular intervals after vaccination and revaccination, blood samples were taken and animals were examined for genital lesions (Blasco et al., 1993).
  
• Side Effects: One ram died from enterotoxemia during the course of the experiment (Blasco et al., 1993).
  
• Challenge Protocol: Challenge inoculations were performed 31 weeks after the second vaccination with a virulent strain of B. ovis obtained from a naturally infected ram. Each ram received a total volume of 60 uL ( 1 x 10^9 CFU), as shown by viable cell counts made on the day of inoculation), both conjunctivally (30 uL) and preputially (30 uL) (Blasco et al., 1993).
• Efficacy: Two weeks after challenge, ten of the 15 control rams excreted B. ovis. All animals were slaughtered 15 weeks after the challenge inoculation and subjected to bacteriological and histological examinations. A ram was classified as protected if no B. ovis was isolated from any of the 13 organs sampled at necropsy. Significant levels of protection in comparison with the control group were obtained by vaccination with 45/20 bacterin (PC 0.05) (Blasco et al., 1993).