Evaluation of tests and diagnostic strategies in bovine brucellosis control and eradication programs

Abstract

Due to the impact of Brucella abortus infection on livestock and public health, the control and eradication of bovine brucellosis is an important goal in several countries where the disease is endemic. The diagnosis of Brucella spp. in brucellosis control and eradication programs is usually based on bacteriological and serological tests. Although important for disease diagnosis, phenotypic typing methods generally have lower discriminatory power compared to genotypic methods and therefore make it difficult to track outbreaks and control disease spread. In this sense, the objective of the present study was to evaluate, in a general context, the guidelines that influence and strategies in a bovine brucellosis control and eradication program, having as specific objectives: to estimate the values of diagnostic sensitivity (DSe) and diagnostic specificity (DSp ) of the main serological tests used in the diagnosis of bovine brucellosis, as well as the estimation of conditional dependence and outline strategies for the reduction and eradication of bovine brucellosis applied to control programs. In addition to assessing the potential risks of using oocytes from animals positive for brucellosis in reproductive biotechnologies and performing a broad phenotypic and genotypic characterization of two strains of B. abortus biovar 4 described for the first time in cattle in Brazil, providing high-resolution epidemiological data on rare isolates of B. abortus among cattle in the country. The main results that we can highlight from the studies that make up this thesis are: the serological tests most used for the diagnosis of bovine brucellosis worldwide showed overestimation of Dse and DSp estimates; all serological tests, except iELISA_SOD, that were evaluated showed conditional dependence; iELISA_SOD can be used for the diagnosis of infected animals, increasing the range of serological tests available for the diagnosis of bovine brucellosis, with the advantage of being free of S-LPS. In contrast, iELISA_MDH showed low utility as a diagnostic test for bovine brucellosis, as well as for differentiating infection from vaccination; even in the ovarian follicular fluid of seropositive cows there is no presence of Brucella spp., which offers greater safety for the reproductive biotechnologies performed from the follicular aspirate of these animals; and the typing of B. abortus strains isolated from cattle in Brazil confirmed the occurrence of B. abortus biovar 4 in the country, providing subsidies for the surveillance of the pathogen within the program for the control and eradication of bovine brucellosis in the country.