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Subject: search.filters.subject.Brucella abortus

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    A novel Bayesian Latent Class Model (BLCM) evaluates multiple continuous and binary tests: A case study for Brucella abortus in dairy cattle.
    (Elsevier B.V., 2024-03-01) Wang Y; Vallée E; Compton C; Heuer C; Guo A; Wang Y; Zhang Z; Vignes M
    Bovine brucellosis, primarily caused by Brucella abortus, severely affects both animal health and human well-being. Accurate diagnosis is crucial for designing informed control and prevention measures. Lacking a gold standard test makes it challenging to determine optimal cut-off values and evaluate the diagnostic performance of tests. In this study, we developed a novel Bayesian Latent Class Model that integrates both binary and continuous testing outcomes, incorporating additional fixed (parity) and random (farm) effects, to calibrate optimal cut-off values by maximizing Youden Index. We tested 651 serum samples collected from six dairy farms in two regions of Henan Province, China with four serological tests: Rose Bengal Test, Serum Agglutination Test, Fluorescence Polarization Assay, and Competitive Enzyme-Linked Immunosorbent Assay. Our analysis revealed that the optimal cut-off values for FPA and C-ELISA were 94.2 mP and 0.403 PI, respectively. Sensitivity estimates for the four tests ranged from 69.7% to 89.9%, while specificity estimates varied between 97.1% and 99.6%. The true prevalences in the two study regions in Henan province were 4.7% and 30.3%. Parity-specific odds ratios for positive serological status ranged from 1.2 to 2.2 for different parity groups compared to primiparous cows. This approach provides a robust framework for validating diagnostic tests for both continuous and discrete tests in the absence of a gold standard test. Our findings can enhance our ability to design targeted disease detection strategies and implement effective control measures for brucellosis in Chinese dairy farms.
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    A scoping review on the epidemiology and public significance of Brucella abortus in Chinese dairy cattle and humans
    (Elsevier B.V., 2024-01-31) Wang Y; Vallée E; Heuer C; Wang Y; Guo A; Zhang Z; Compton C
    Brucellosis, caused by Brucella spp., is a re-emerging One Health disease with increased prevalence and incidence in Chinese dairy cattle and humans, severely affecting animal productivity and public health. In dairy cattle, B. abortus is the primary causative agent although infections with other Brucella species occur occasionally. However, the epidemiological and comparative importance of B. abortus in dairy cattle and humans remains inadequately understood throughout China due to the heterogeneity in locations, quality, and study methods. This scoping review aims to describe the changing status of B. abortus infection in dairy cattle and humans, investigate the circulating Brucella species and biovars, and identify factors driving the disease transmission by retrieving publicly accessible literature from four databases. After passing the prespecified inclusion criteria, 60 original articles were included in the final synthesis. Although the reported animal-level and farm-level prevalence of brucellosis in dairy cattle was lower compared to other endemic countries (e.g. Iran and India), it has been reported to increase over the last decade. The incidence of brucellosis in humans displayed seasonal increases. The Rose Bengal Test and Serum Agglutination Test, interpreted in series, were the most used serological test to diagnose Brucella spp. in dairy cattle and humans. B. abortus biovar 3 was the predominant species (81.9%) and biovar (70.3%) in dairy cattle, and B. melitensis biovar 3 was identified as the most commonly detected strain in human brucellosis cases. These strains were mainly clustered in Inner Mongolia and Shannxi Province (75.7%), limiting the generalizability of the results to other provinces. Live cattle movement or trade was identified as the key factor driving brucellosis transmission, but its transmission pattern remains unknown within the Chinese dairy sector. These knowledge gaps require a more effective One Health approach to be bridged. A coordinated and evidence-based research program is essential to inform regional or national control strategies that are both feasible and economical in the Chinese context.
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    Serological diagnosis of Brucella infection :a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, New Zealand
    (Massey University, 1978) Timbs, Derek Vernon
    The automated complement fixation test (CFT) and the brucellosis card test (BCT) have been widely used as official tests in the New Zealand Bovine Brucellosis Eradication Scheme. During the course of the eradication programme it was observed that a significant proportion of cattle reacted to the BCT yet remained negative to the CFT and this often occurred on more than one occasion for any particular animal. Twenty cows, from reactor herds, that had been BCT+/CFT- on at least three successive occasions were slaughtered. Despite extensive sampling, attempts at isolating Brucella abortus organisms from tissues of these animals were unsuccessful. Serum from one cow was found to be positive to a wide range of serological tests and it also caused a strong prozone reaction in the CFT, which could easily have been overlooked. The possibility that the automated CFT, which is essentially a one dilution test, was unable to detect such prozoning sera was investigated. It was shown that providing a suitable choice of antigen concentration was made, such sera would be detected by the automated test. Brucella - specific IgG1, IgG2, and IgM levels in Prozoning and non prozoning sera were measured using the single radial immunodiffusion test. It was shown that serum containing a high proportion of specific IgG2 was likely to exhibit prozoning and that various degrees of prozoning could be induced by varying the ratio of specific IgG1 to specific IgG2. Cattle, previously sensitized by calfhood Br. abortus strain 19 vaccination, were experimentally inoculated with killed Br. abortus. It was shown that although serum agglutination test (SAT) and CFT titres appeared for a short period, titres to the BCT in some cattle tended to remain longer thus allowing an animal to be BCT+/CFT-. An analysis of herd testing data indicated that BCT+/CFT-animals were more likely to exist in infected herds than in non-infected herds. In heavily infected herds up to 16% of CFT- animals were BCT+ whereas in non-infected or very lightly infected herds less than 4% were CFT-/BCT+. It was concluded that in sensitized cattle at least exposure to the organism without true infection is capable of stimulating antibody which is detected by the BCT, but not necessarily able to provoke positive CFT titres. The performance of the Auto-Analyzer adaptation of the CFT as used in the New Zealand eradication scheme was assessed. Various prozoning sera from known infected animals were tested and the effect of varying antigen concentrations on these and other sera was noted. Significant differences in antigen concentration required for optimal complement fixation were detected. Prozoning sera required more antigen than non-prozoning sera and even sera that did not exhibit prozoning had varying optimal antigen requirements. By using I125 labelled bovine gama-globulin the dilution gradient of serum within the Auto-Analyzer system was estimated. Knowledge of the serum dilution gradient being obtained was essential for proper understanding of unusual traces given by prozoning sera.