Evaluation of Primary Binding Assays for Presumptive Serodiagnosis of Swine Brucellosis in Argentina

Abstract

An indirect enzyme-linked immunosorbent assay (IELISA), a competitive ELISA (CELISA), and a fluorescence polarization assay (FPA) for the presumptive serological diagnosis of swine brucellosis were evaluated using two populations of swine sera: sera from brucellosis-free Canadian herds and sera from Argentina selected based on positive reactions in the buffered antigen plate agglutination test (BPAT) and the 2-mercaptoethanol (2-ME) test. In addition, sera from adult swine from which Brucella suis was isolated at least once for each farm of origin were evaluated. The IELISA, CELISA, and FPA specificity values were 99.9, 99.5, and 98.3%, respectively, and the IELISA, CELISA, and FPA sensitivity values relative to the BPAT and the 2-ME test were 98.9, 96.6, and 93.8%, respectively. Actual sensitivity was assessed by using 37 sera from individual pigs from which B. suis was cultured, and the values obtained were as follows: BPAT, 86.5%; 2-ME test, 81.1%; IELISA, 86.5%; CELISA, 78.5%; and FPA, 80.0%.Brucella suis occurs naturally in the smooth phase. The smooth Brucella spp. share certain smooth lipopolysaccharide (SLPS) epitopes, resulting in extensive serological cross-reactions. For this reason, conventional serological tests for swine brucellosis use antigens from Brucella abortus rather than B. suis, as shown by extensive testing for swine brucellosis in the United States (6). Conventional serological tests (16) and indirect enzyme-linked immunosorbent assays (IELISAs) (4, 16) cannot identify animals infected with Yersinia enterocolitica O:9 because of epitopes shared with Brucella spp. (16), resulting in lower specificity values than assays such as the competitive ELISA (CELISA) and the fluorescence polarization assay (FPA), which are capable of distinguishing animals infected with cross-reacting microorganisms (8, 9, 15) or vaccinated with B. abortus strain 19 (11) from animals infected with B. abortus or B. suis. The specificity of conventional serological agglutination tests was further reduced by nonspecific antibody thought to be immunoglobulin M (IgM) (16).Due to the uncertain nature of serological reactions to Brucella in pigs, the screening buffered antigen plate agglutination test (BPAT) (2) and the 2-mercaptoethanol (2-ME) agglutination test (7) are currently used for the detection of B. suis in infected herds. Only a few studies have described the development of primary binding assays for the detection of antibody to B. suis (17,20).More recently the IELISA, the CELISA, and the FPA developed for the diagnosis of bovine brucellosis (10, 14) have been validated for the presumptive diagnosis of swine brucellosis (15). The aims of the present study were to evaluate the IELISA, CELISA, and FPA for diagnosis of porcine brucellosis in Argentina, compared with the BPAT and 2-ME test used as diagnostic tests in Argentina, and to confirm previous data. MATERIALS AND METHODSNegative sera. Sera from Canadian pigs with no clinical or epidemiological evidence of brucellosis (B. suis has not been detected in Canad...

Diagnostic Characterization of a Feral Swine Herd Enzootically Infected withBrucella

“…One animal yielded only RB51 on bacteriologic culture, and that animal was excluded from the sensitivity estimates as RB51, being O-polysaccharide deficient, does not induce detectable immune responses by the 3 assays used in this study. 21,29 The sensitivity rates of both the STT (P , 0.0001) and FPA (P , 0.005) assays were significantly higher than the Card Test but did not differ from each other.…”

“…Previously published sensitivity rates for these assays in domestic swine were 20-67% for the card test, 83-100% for the standard tube test, and 80-94% for the FPA test. 13,18,21 The sensitivity rates for individual assays calculated in this study, however, were 13.1% for the card test, 44.6% for the standard tube test, and 42.6% for the fluorescence polarization assay. Antigens used in these assays are from B. abortus, which may at least partially account for the lack of sensitivity when evaluating swine presumably infected with B. suis.…”

“…Serum was divided into 1-ml aliquots, and stored at 270uC until assays were performed. Brucella serologic status of all animals was determined by fluorescence polarization (FPA), 21 standard tube agglutination (STT), 1 and card agglutination assays 1 by previously described methods. Animals that had a positive reaction on at least 1 of the 3 serologic assays were considered positive seroreactors.…”

Seroprevalence of Brucellosis from Pigs: The First Report in Central Ethiopia

“…The variation in this seroprevalence might have been due the disparity in geographical locations, climatic conditions and management practices in the different study areas. Other studies have also indicated that the rate of brucellosis infection varies among pig herds, from farm to farm or by country [30][31][32] by origin of tested pigs (wild or domesticated) [30] and by testing method used [33]. Furthermore, contact with other animals was also reported to be major risk factors that were influencing the occurrence brucellosis [34].…”

Brucella infection and vaccine studies in feral and domestic swine

“…172 The reported sensitivity of the FPA assay is 63.0%-98.9%, and the specificity is reported to be 55.0%-99.9%. 152,173,194 The FPA studies utilized sera which was previously determined to be positive by the BPAT or 2-ME assays; therefore, the sensitivity values are likely inappropriately high.…”