Systematic review on the effectiveness of Brucella abortus S19 and RB51 vaccine strains in field studies

Brucella abortus S19 and RB51 are the most used vaccines to control bovine brucellosis worldwide; therefore, this study aimed to perform a systematic review on the effectiveness of these two vaccine strains in field studies. The literature review was conducted on April 3rd 2020 on six databases (CABI, Cochrane, PubMed, Scielo, Scopus and Web of Science) and included papers published between 1976 and 2016. The search strategy recovered a total of 5846 papers on databases and 6 papers were included due to specialists' suggestions. After selection, 17 papers were included, in which 33 trials were identified. Most trials [63.63 % (21/33)] used prevalence panel design (cross-sectional), while the others were cohort studies. S19 strain was used in most of the trials [75.76 % (25/33)], mainly by subcutaneous route [84.00 % (21/25)] and in adult cattle [76.00 % (19/25)]. RB51 strain was administrated only by the subcutaneous route and in both young and adult animals. For case definition, complement fixation [60.60 % (20/33)] and rivanol [30.30 % (10/33)] were the most used tests. Twenty of the 33 trials (60.61 %) showed significant effect of vaccination on brucellosis control, with lower incidence of infection in the vaccinated groups (in cohort trials) or reduced prevalence after vaccination (in prevalence panels); however, the great heterogeneity observed among the studies precluded a meta-analysis from the data extracted. In addition, most trials [57.57 % (19/33)] adopted other control measures (test-and-slaughter or isolation of positive animals from the herd) in association with vaccination, which harmed the better understand of the isolated effect of vaccination for brucellosis control in field in these studies. In conclusion, the result from this review suggests that both S19 and RB51 vaccine strains are effective in reducing brucellosis incidence in both calves and adults, as well as abortion rates, mainly when associated to other control policies.