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Bayesian evaluation of three serological tests for the diagnosis of bovine brucellosis in Bangladesh.

ABSTRACT: We evaluated the performance of three serological tests - an immunoglobulin G indirect enzyme linked immunosorbent assay (iELISA), a Rose Bengal test and a slow agglutination test (SAT) - for the diagnosis of bovine brucellosis in Bangladesh. Cattle sera (n = 1360) sourced from Mymensingh district (MD) and a Government owned dairy farm (GF) were tested in parallel. We used a Bayesian latent class model that adjusted for the conditional dependence among the three tests and assumed constant diagnostic accuracy of the three tests in both populations. The sensitivity and specificity of the three tests varied from 84.6% to 93.7%, respectively. The true prevalences of bovine brucellosis in MD and the GF were 0.6% and 20.4%, respectively. Parallel interpretation of iELISA and SAT yielded the highest negative predictive values: 99.9% in MD and 99.6% in the GF; whereas serial interpretation of both iELISA and SAT produced the highest positive predictive value (PPV): 99.9% in the GF and also high PPV (98.9%) in MD. We recommend the use of both iELISA and SAT together and serial interpretation for culling and parallel interpretation for import decisions. Removal of brucellosis positive cattle will contribute to the control of brucellosis as a public health risk in Bangladesh.

SUBMITTER: Rahman AKMA

PROVIDER: S-EPMC6518595 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Bayesian evaluation of three serological tests for the diagnosis of bovine brucellosis in Bangladesh.

Rahman A K M A AKMA Smit S S Devleesschauwer B B Kostoulas P P Abatih E E Saegerman C C Shamsuddin M M Berkvens D D Dhand N K NK Ward M P MP

Epidemiology and infection 20190101

We evaluated the performance of three serological tests - an immunoglobulin G indirect enzyme linked immunosorbent assay (iELISA), a Rose Bengal test and a slow agglutination test (SAT) - for the diagnosis of bovine brucellosis in Bangladesh. Cattle sera (n = 1360) sourced from Mymensingh district (MD) and a Government owned dairy farm (GF) were tested in parallel. We used a Bayesian latent class model that adjusted for the conditional dependence among the three tests and assumed constant diagno ...[more]

PMID: 30869026

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Project description:BACKGROUND:The culture has always been the gold standard test for diagnosis of human brucellosis but the conventional Brucella diagnostic tests viz. serology and culture are often beset with poor specificity & sensitivity respectively. The culture positivity rates for Brucella vary from 92% for bone marrow to 10% for non-blood samples and also dependent on the type of sample. The primary immune-determinant for Brucella species is the cell wall surface lipopolysaccharide, which is antigenically similar to other gram-negative rods. Hence, Brucella serological tests cross react with Escherichia coli 0116 and 0157, Salmonella urbana, Yersinia enterocolitica 0:9, Vibrio cholerae, Xanthomonas maltophilia and Afipia clevellandensis infections, which are common in developing countries also having higher incidence of brucellosis. AIM:The aim of the study was evaluation of conventional serological techniques and PCR for diagnosis of human brucellosis in and around north Karnataka which is endemic for brucellosis and patients often present with elevated base line antibody titers and confounding clinical manifestations. MATERIALS AND METHODS:Blood/serum samples of 400 patients suffering from acute undifferentiated fever (AUF) were subjected to culture, Brucella slide agglutination test (SAT), standard tube agglutination test (STAT coupled with 2 ME) and PCR. RESULTS:Of the 400 AUF patients, anti-Brucella antibodies were detected by SAT and STAT in serum of 35 and 34 patients respectively. IS711 gene for Brucella was identified in 32 patients by PCR. Twenty samples yielded Brucella in culture on biphasic medium with average incubation period of 9 days. All patients having titer of ? 160IU / ml in STAT were found positive by PCR also. CONCLUSION:Brucella STAT corroborated well with PCR results in all those cases where antibodies were present at least one dilution above cut-off value of 80 IU/ml. We probably need to raise cut-off titers to ?160 IU/ml because of endemic region. The SAT was upheld as very good quick, easy to perform and economical screening test for human brucellosis. SAT as rapid screening test and STAT as more definitive test can be very well adopted by laboratories working in resource scarce settings for diagnosis of human brucellosis in absence of PCR even for population with normally elevated antibodies levels due to residing in Brucella endemic areas.

Project description:BackgroundBovine tuberculosis (BTB) today primarily affects developing countries. In Africa, the disease is present essentially on the whole continent; however, little accurate information on its distribution and prevalence is available. Also, attempts to evaluate diagnostic tests for BTB in naturally infected cattle are scarce and mostly complicated by the absence of knowledge of the true disease status of the tested animals. However, diagnostic test evaluation in a given setting is a prerequisite for the implementation of local surveillance schemes and control measures.Methodology/principal findingsWe subjected a slaughterhouse population of 954 Chadian cattle to single intra-dermal comparative cervical tuberculin (SICCT) testing and two recently developed fluorescence polarization assays (FPA). Using a Bayesian modeling approach we computed the receiver operating characteristic (ROC) curve of each diagnostic test, the true disease prevalence in the sampled population and the disease status of all sampled animals in the absence of knowledge of the true disease status of the sampled animals. In our Chadian setting, SICCT performed better if the cut-off for positive test interpretation was lowered from >4 mm (OIE standard cut-off) to >2 mm. Using this cut-off, SICCT showed a sensitivity and specificity of 66% and 89%, respectively. Both FPA tests showed sensitivities below 50% but specificities above 90%. The true disease prevalence was estimated at 8%. Altogether, 11% of the sampled animals showed gross visible tuberculous lesions. However, modeling of the BTB disease status of the sampled animals indicated that 72% of the suspected tuberculosis lesions detected during standard meat inspections were due to other pathogens than Mycobacterium bovis.Conclusions/significanceOur results have important implications for BTB diagnosis in a high incidence sub-Saharan African setting and demonstrate the practicability of our Bayesian approach for diagnostic test evaluation.

Project description:Brucellosis is a neglected endemic zoonosis in Bangladesh and has a significant impact on public health and animal welfare of dairy farming as well as dairy farm economics. A cross-sectional study was conducted to evaluate the seroprevalence of and risk factors for brucellosis in dairy cattle in the Chittagong metropolitan area (CMA) of Chittagong, Bangladesh. We collected serum samples (n = 158) from six randomly selected dairy farms in the CMA between February and November, 2015. The Rose Bengal Plate Test (RBPT) and a competitive ELISA (cELISA) were used as the screening and confirmatory tests respectively. Farm level and animal level demographic and risk factor data were collected using a questionnaire. The risk factors were analysed using a multivariable logistic regression with random effects. The overall seroprevalences of antibodies against brucellosis in cattle were 21.5% (34/158) and 7.6% (12/158) based on parallel and serial interpretation of the two tests respectively. Our results revealed that 20.3% (32/158) samples were positive using the RBPT and 8.9% (14/158) were positive using the cELISA. The within-herd seroprevalence ranged from 10% to 26.3% and 5 to 20.7% using the RBPT and cELISA tests respectively. The odds of seropositivity were significantly higher in lactating cows (OR: 2.59; 95% CI: 1.02-6.55), cows producing less than 2 litres of milk (OR: 29.6; 95% CI: 4.3-353.8), cow producing 2-12 litres of milk (OR: 4.8; 95% CI: 1.1-33.4) and cows with reproductive disorders (OR: 3.2; 95% CI: 1.2-10.1). About 7.6% (12/158) and 1.3% (2/158) of cattle were found to be infected with acute and chronic brucellosis respectively. Based on these results, we suggest that cows that have reproductive disorders and are producing little milk should be prioritized for brucellosis screening in CMA. The screening tests should be used to control brucellosis in cattle in order to protect animal welfare, human health and to minimize the economic losses.

Dataset Information

Bayesian evaluation of three serological tests for the diagnosis of bovine brucellosis in Bangladesh.

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Bayesian evaluation of three serological tests for the diagnosis of bovine brucellosis in Bangladesh.

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