Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2006
Publication Date: 4/27/2006
Citation: Poester, F.P., Goncalves, V.S., Paixao, T.A., Santos, R.L., Olsen, S.C., Schurig, G., Lage, A.P. 2006. Efficacy of strain RB51 vaccine in heifers against experimental brucellosis. Vaccine. 24(2006):5327-5334. Interpretive Summary: Brucellosis, a disease characterized by abortion and fetal losses, remains endemic in domestic livestock in many areas worldwide. Infection of cattle with B. abortus poses a significant health risk for transmission to humans by direct contact or from consumption of unpasturized milk and can cause a wide range of clinical symptoms in humans including the classical syndrome of Aundulant fever@. Although the Brucella abortus strain RB51 vaccine has been used in the United States since 1996, other countries require independent studies before they consider use of this vaccine. In this collaborative study, the strain RB51 vaccine was demonstrated to reduce abortion or infection in adult heifers after experimental challenge. The safety of the vaccine was also demonstrated as abortions were not noted and vaccinates remained negative on surveillance tests. Based on this data, RB51 vaccine is being considered for use in Brazil. The implementation of RB51 vaccine use in Brazil will reduce the prevalence of brucellosis in that country. This will benefit producers and regulatory personnel in the United States by preventing the development of artificial trade barriers, and also by reducing the risk of brucellosis associated with importation of cattle from Brazil.
Technical Abstract: With the goal of providing an additional tool for controlling bovine brucellosis in Brazil, the efficacy of the rough Brucella abortus strain RB51 vaccine was tested in heifers. Thirty-three females with approximately 24 months of age were divided in two groups: RB51 vaccinated (n=20) and non-vaccinated control (n=13). Animals in the vaccinated group were split in two sub-groups. One sub-group (n=12) was vaccinated subcutaneously with 1.5x10^10 colony forming units (CFU) of RB51 at day 0 of the experiment and the other sub-group (n=8) was vaccinated subcutaneously with 1.6x10^10 CFU of RB51 at 60 days of gestation (day 260 of the experiment). All cattle were challenged between 6 and 7 months of pregnancy with 3x10^8 CFU of the virulent strain 2308 of B. abortus by the conjunctival route. Vaccination with RB51 did not result in the production of any antibodies against the O-side chain of lipopolysacharide, as measured by conventional serological tests. A total of 25% cumulative incidence of abortions was found in the vaccinated group, whereas in the control group the cumulative incidence was 62%. The vaccine strain was not isolated from any tissue sample, and no abortions were produced by the RB51 vaccine when used in females at 60 days of pregnancy. Our results indicate that vaccination with RB51 prevented 59.4% of abortions, 58.6% of cow infections, and 61.0% of fetal infections. The relative risk revealed that non-vaccinated animals have 2.462 (95% CI - 1.029 to 5.889) times higher risk of aborting than RB51-vaccinated animals.