Efficacy of strain RB51 vaccine in protecting infection and vertical transmission against Brucella abortus in Sprague-Dawley rats

Abstract

Immunizing animals in the wild against Brucella (B.) abortus is essential to control bovine brucellosis because cattle can get the disease through close contact with infected wildlife. The aim of this experiment was to evaluate the effectiveness of the B. abortus strain RB51 vaccine in protecting infection as well as vertical transmission in Sprague-Dawley (SD) rats against B. abortus biotype 1. Virgin female SD rats (n = 48) two months of age were divided into two groups: one group (n = 24) received RB51 vaccine intraperitoneally with 3 x 10(10) colony forming units (CFU) and the other group (n = 24) was used as non-vaccinated control. Non-vaccinated and RB51-vaccinated rats were challenged with 1.5 x 10(9) CFU of virulent B. abortus biotype 1 six weeks after vaccination. Three weeks after challenge, all rats were bred. Verification of RB51-vaccine induced protection in SD rats was determined by bacteriological, serological and molecular screening of maternal and fetal tissues at necropsy. The RB51 vaccine elicited 81.25% protection in SD rats against infection with B. abortus biotype 1. Offspring from rats vaccinated with RB51 had a decreased (p < 0.05) prevalence of vertical transmission of B. abortus biotype 1 compared to the offspring from non-vaccinated rats (20.23% and 87.50%, respectively). This is the first report of RB51 vaccination efficacy against the vertical transmission of B. abortus in the SD rat model.

Fig. 1

Bruce-ladder multiplex PCR assay. Lane 1: DNA molecular weight standard marker; Lane 2: bacterial DNA of non-vaccinated rat; Lane 3: bacterial DNA of RB51-vaccinated rat; Lane 4: bacterial DNA of offspring born to non-vaccinated dam; Lane 5: bacterial DNA of offspring born to RB51-vaccinated dam; Lane 6: positive control with DNA of Brucella (B.) abortus strain 1119-3; Lane 7: positive control with DNA of B. abortus strain RB51; Lane 8: negative control without DNA.

Fig. 2

Standard tube agglutination titers of rats 3 weeks after challenge with B. abortus biotype 1 and at necropsy. Antibody titers are reported as mean ± SE. Statistically significant differences among RB51-vaccinated, non-vaccinated pregnant and non-pregnant control rats are indicated by asterisks (^*p < 0.05 and ^†p < 0.001).

Fig. 3

Total serum IgG, IgG1 and IgG2a levels of non-vaccinated control and RB51-vaccinated rats 3 weeks after challenge with B. abortus biotype 1 (A) and at necropsy (B). Antibody titers are reported as mean ± SE. Statistically significant difference among RB51-vaccinated, non-vaccinated pregnant and non-pregnant control rats are indicated by asterisks (^*p < 0.05 and ^†p < 0.001).