Some Serological Analytic Approaches and Test Execution in Determination of Bovine Brucellosis: Overview

Abstract

Bovine brucellosis is a highly contagious, zoonotic, and economically significant bacterial disease. The purpose of this paper was to review available scientific data on serological tests for the diagnosis of bovine brucellosis and compare test performance based on assay sensitivity (Se) and specificity (Sp) values. Abortion, placentitis, epididymitis, and orchitis are symptoms of the disease. The clinical picture of brucellosis is not pathognomonic, and the patient's clinical history, particularly the occurrence of abortion, is crucial for diagnosis. Although the causative agent is isolated and identified for a definitive diagnosis of bovine brucellosis, serological tests are usually preferred. The host defense mechanism against Brucella is functionally divided into innate or non-specific immunity and adaptive or specific immunity. The pathogenic brucella organism has evolved a slew of mechanisms for evading and/or modulating both innate and adaptive immune responses in its host. Serological assays are based on the fact that Brucella abortus and other smooth Brucella have a unique O-polysaccharide that induces a humoral response with the production of IgM first, followed by IgG1, and then IgG2/IgA. Screening serological tests (Milk ring test, Rose Bengal Test (RBT), and Buffered plate agglutination test (BPAT)) and confirmatory serological tests (complement fixation test (CFT), serum agglutination test (SAT), 2-mercaptoethanol test (2ME), indirect-enzyme-linked immunosorbent assay (iELISA), and, more recently, competitive-ELISA (cELISA) and Brucella fluorescent pol (FPA). CFT, RBT, and iELISA tests are currently used in EU legislation for intra-community cattle trade and show comparable Se and Sp. The new FPA test demonstrated Se and Sp levels comparable to standard tests and was proposed for inclusion as a standard test in EU legislation. Similarly, the OIE considers the four tests to be a mandatory requirement for international trade. Several methods, however, produce both false-positive and false-negative results. There is no single serological test that is 100% accurate and applicable in all epidemiological situations. In general, confirmatory serological procedures involve testing each serum with multiple tests, usually a screening test with high sensitivity followed by a confirmatory test with high specificity. As a result, the development of rapid, low-cost serological tests with high sensitivity and specificity for brucellosis detection is a major issue that requires further investigation.

Keywords: Bovine Brucellosis; Brucella Abortus; Diagnosis; Sensitivity; Specificity; Serological Tests, Test Performance

DOI: 10.7176/JNSR/13-12-03

Publication date:June 30^th 2022