Bayesian estimation of the true prevalence, sensitivity and specificity of the Rose Bengal and indirect ELISA tests in the diagnosis of bovine brucellosis

Determination of seroprevalence of brucellosis in livestock and high-risk population in Kurdistan, Western Iran

BACKGROUND

Brucellosis is one of the most prevalent zoonotic diseases. Using serological tests are valid and rapid methods that could be used in the detection of the history of getting brucellosis. Considering that Iran is an endemic country for brucellosis, we aimed to investigate the rate of seroprevalence of brucellosis among livestock and human in Kurdistan province.

MATERIAL AND METHOD

Serum sampling was performed from 51 slaughterhouse workers, veterinarians, and husbandry workers, along with 260 livestock (80 cattle, 120 sheep, and 60 goats). Rose Bengal plate test (RBPT), and Enzyme-linked immunosorbent assay (ELISA) were used for livestock and the anti-Brucella IgG antibody was evaluated in human participants.

RESULTS

The seroprevalence (based on ELISA assay) in sheep, goats, and cows was 5.8%, 5%, and 1.2%, respectively. Also, the rate of anti-Brucella IgG was 3.9% among human participants.

DISCUSSION

the current study, provided some valuable information on the seroprevalence of brucellosis in animal and human participants from the west of Iran. Considering the effects of brucellosis on causing reproductive disorders, including abortion, placental retention, andendometritis controlling the infection could have a significant impact on terms of economy.

Human and Animal Brucellosis in Nigeria: A Systemic Review and Meta-Analysis in the Last Twenty-One Years (2001–2021)

Simple Summary

Brucellosis caused by Brucella spp. is transmitted by direct or indirect contact with infected animals or their secretions and through the consumption of infected animal meat and unpasteurized milk/milk products. Brucellosis is classified as one of the top neglected zoonosis by the World Health Organization (WHO), and despite this, it does not attract the appropriate attention it requires from both the Federal and State ministries of health in Nigeria. Currently, there is a lack of coordinated national data on the prevalence and distribution of human and animal brucellosis. Thus, published research works between 2001 and 2021 were studied based on set criteria to estimate the burden and distribution of brucellosis in Nigeria. The results of the national seroprevalence of human and animal brucellosis were 17.6% (554/3144) and 13.3% (8547/64,435), respectively. Specifically, 15.8% (7178/45,363) seroprevalence of brucellosis was recorded in northern Nigeria as against 8.7% (1902/21,740) in the southern part. Brucella abortus, B. melitensis, B. suis, and B. canis were reported in 27 of the 36 states. Improved sanitation at the abattoirs, use of personal protective equipment by animal handlers, vaccination of animals against brucellosis, and ranching of animals to curb the spread of the disease should be paramount to all stakeholders.

Abstract

The global burden of human and animal brucellosis remains enormous. The disease, which is endemic in Nigeria, lacks appropriate attention and national data. This review estimated the burden and distribution of human and animal brucellosis in Nigeria in the last twenty-one years (2001–2021). Publications reporting the detection of brucellosis in Nigeria were sorted from different search engines, including PubMed, ResearchGate, Scopus, and Google Scholar, to generate data on its prevalence, spatial distribution, and predisposing factors. The results of the national seroprevalence of human and animal brucellosis as revealed in this study were 17.6% (554/3144) and 13.3% (8547/64,435), respectively. Specifically, 15.8% (7178/45,363) seroprevalence of brucellosis was recorded in northern Nigeria as against 8.7% (1902/21,740) seroprevalence in the southern part. It also indicated that 78.7% of the detected brucellae were un-typed. The Brucella species detected were B. abortus (15.2%), B. melitensis (4%), B. suis (1.8%), and B. canis (0.4%). This study revealed that brucellosis is endemic in Nigeria. Culture and molecular methods for detecting brucellosis and reports on antimicrobial susceptibility testing remain a conjecture. This review will help researchers redirect their research focus and serve as a guide for policymakers on measures for managing brucellosis in Nigeria.

Bayesian Estimation of the Prevalence and Test Characteristics (Sensitivity and Specificity) of Two Serological Tests (RB and SAT-EDTA) for the Diagnosis of Bovine Brucellosis in Small and Medium Cattle Holders in Ecuador

In Ecuador, a national program for bovine brucellosis control has been in implementation since 2008. Given the costs, small- and medium-sized livestock holders are not completely committed to it. The objective of this study was to determine true prevalence (TP) of bovine brucellosis in small- and medium-sized herd populations, as well as the diagnostic sensitivity and specificity of the Rose Bengal (RB) test and the sero-agglutination test (SAT)-EDTA using a Bayesian approach. Between 2011 and 2016, 2733 cattle herds were visited, and 22,592 animal blood samples were taken in nineteen provinces on mainland Ecuador. Bayes-p and deviance information criterion (DIC) statistics were used to select models. Additionally, risk-factor analysis was used for herds according to their brucellosis test status. True prevalence (TP) in herds was estimated by pool testing. National seroprevalence of farms was 7.9% (95% CI: 6.79–9.03), and TP was 12.2% (95% CI: 7.8–17.9). Apparent prevalence (AP) in animals was 2.2% (95% CI: 1.82–2.67), and TP was 1.6% (95% CrI: 1.0–2.4). Similarly, the sensitivity of the RB was estimated at 64.6% (95% CrI: 42.6–85.3) and specificity at 98.9% (95% CrI: 98.6–99.0); for the SAT-EDTA test, sensitivity was 62.3% (95% CrI: 40.0–84.8) and 98.9% (95% CrI: 98.6–99.1) for specificity. Results of the two tests were highly correlated in infected and uninfected animals. Likewise, high spatial variation was observed, with the Coastal Region being the zone with the highest TP at 2.5%. (95% CrI: 1.3–3.8%) in individual animals and 28.2% (95% CI: 15.7–39.8) in herds. Risk factors include herd size, type of production (milk, beef, and mixed), abortions recorded, and vaccination. The results of this study serve to guide authorities to make decisions based on parallel testing at the beginning of a bovine brucellosis program for small livestock holders to increase sensitivity level of the screening tests in Ecuador.

Latent class evaluation of the performance of serological tests for exposure to Brucella spp. in cattle, sheep, and goats in Tanzania

BACKGROUND

Brucellosis is a neglected zoonosis endemic in many countries, including regions of sub-Saharan Africa. Evaluated diagnostic tools for the detection of exposure to Brucella spp. are important for disease surveillance and guiding prevention and control activities.

METHODS AND FINDINGS

Bayesian latent class analysis was used to evaluate performance of the Rose Bengal plate test (RBT) and a competitive ELISA (cELISA) in detecting Brucella spp. exposure at the individual animal-level for cattle, sheep, and goats in Tanzania. Median posterior estimates of RBT sensitivity were: 0.779 (95% Bayesian credibility interval (BCI): 0.570-0.894), 0.893 (0.636-0.989), and 0.807 (0.575-0.966), and for cELISA were: 0.623 (0.443-0.790), 0.409 (0.241-0.644), and 0.561 (0.376-0.713), for cattle, sheep, and goats, respectively. Sensitivity BCIs were wide, with the widest for cELISA in sheep. RBT and cELISA median posterior estimates of specificity were high across species models: RBT ranged between 0.989 (0.980-0.998) and 0.995 (0.985-0.999), and cELISA between 0.984 (0.974-0.995) and 0.996 (0.988-1). Each species model generated seroprevalence estimates for two livestock subpopulations, pastoralist and non-pastoralist. Pastoralist seroprevalence estimates were: 0.063 (0.045-0.090), 0.033 (0.018-0.049), and 0.051 (0.034-0.076), for cattle, sheep, and goats, respectively. Non-pastoralist seroprevalence estimates were below 0.01 for all species models. Series and parallel diagnostic approaches were evaluated. Parallel outperformed a series approach. Median posterior estimates for parallel testing were ≥0.920 (0.760-0.986) for sensitivity and ≥0.973 (0.955-0.992) for specificity, for all species models.

CONCLUSIONS

Our findings indicate that Brucella spp. surveillance in Tanzania using RBT and cELISA in parallel at the animal-level would give high test performance. There is a need to evaluate strategies for implementing parallel testing at the herd- and flock-level. Our findings can assist in generating robust Brucella spp. exposure estimates for livestock in Tanzania and wider sub-Saharan Africa. The adoption of locally evaluated robust diagnostic tests in setting-specific surveillance is an important step towards brucellosis prevention and control.

Bayesian Evaluation of Three Serological Tests for Detecting Antibodies against Brucella spp. among Humans in the Northwestern Part of Ecuador

Brucellosis is an important but neglected zoonosis that causes serious economic losses both in livestock and human populations. The aim of the present study was to estimate the true prevalence of brucellosis together with diagnostic sensitivity and specificity of three serological tests in humans of the northwestern part of Ecuador using a Bayesian approach adjusted for the dependencies among the multiple tests to avoid any misinterpretation. In addition, the causal agent responsible for human brucellosis was also identified. Using a total of 3,733 samples collected from humans in this area between 2006 and 2008, the prevalence of human brucellosis and the diagnostic test characteristics of the Rose Bengal fast agglutination test (RBT), Wright's slow agglutination test with ethylenediaminetetraacetic acid disodium salt dehydrate (EDTA) (SAT-EDTA), and indirect ELISA (iELISA) were estimated using a Bayesian approach. The estimated true prevalence of human brucellosis was 1% (credibility interval: 0.4-1.6). The sensitivities of iELISA and RBT were higher than and similar (95.1% and 95.0%, respectively) to those of SAT-EDTA (60.8%). Even though all tests indicated a high specificity (> 99.0%), the specificity of SAT-EDTA was highest (99.9%). The circulating strain in this study area was identified to be Brucella abortus biotype 4 based on culture and microbiological characterization. The RBT and the iELISA are recommended for estimating the true prevalence of human brucellosis and/or for surveillance programs following their high sensitivities and specificities. The proposed strategy supports evidence-based medicine for clinicians and policy-makers to ensure appropriate preventive and control program of brucellosis worldwide.

Bayesian estimation of herd-level prevalence and risk factors associated with BoHV-1 infection in cattle herds in the State of Paraíba, Brazil

A cross-sectional study was carried out to estimate the animal- and herd-level prevalence of bovine herpesvirus 1 (BoHV-1) infection in cattle in the State of Paraíba, and to identify risk factors associated with herd-level infection. The state was divided into three sampling strata, and for each stratum, the prevalence of herds infected with BoHV-1 was estimated through a two-stage sampling survey carried out from September 2012 to January 2013. In total, 2443 animals were sampled from 478 herds. A virus-neutralization test was used for BoHV-1 antibody detection. A Bayesian latent-class model was used to describe the data, taking into account imperfect diagnostic test characteristics and the non-independence of test results from animals within the same herd, and using a dynamic within-model risk factor selection method based on indicator variable selection. The adjusted herd-level prevalence was estimated to be 84% (95% CI: 80-88%) for the State of Paraíba, and the animal-level prevalence was estimated to be 73% (95% CI: 66-84%). Only five of the available risk factors were used by the model, with the three most influential being disposal of aborted foetuses (3.78, 95% CI: 1.11-13.85), sharing resources with other farms (3.0, 95% CI: 1.1-8,6), and a herd size of > 23 animals (2.5, 95% CI: 1.1-6.0). Our findings suggest that the animal- and herd-level seroprevalence of BoHV-1 infection in the State of Paraíba is high. While some risk factors such as herd size and sharing resources were identified as risk factors for BoHV-1 infection, these risk factors are initially likely to be of only minor relevance in a control programme due to the extremely high prevalence of infected farms. However, the results are relevant to the risk of reintroduction of disease on farms that have previously eradicated the disease.

Development of an indirect ELISA based on whole cell Brucella abortus S99 lysates for detection of IgM anti-Brucella antibodies in human serum

BACKGROUND

Brucellosis is the most common zoonotic diseases worldwide. The aim of this study was to develop and evaluate the diagnostic performance of an indirect-ELISA (I-ELISA) method based on whole cell Brucella abortus S99 lysates for detection of IgM anti-Brucella antibodies in a human serum.

MATERIALS AND METHODS

The study was conducted in two species-rich endemic areas of Iran (Tehran and Lorestan provinces). Serum samples of 102 patients and 150 healthy individuals were tested by the new kit and the commercial Vircell kit for the presence of anti-Brucella IgM antibodies. The disease status was confirmed by Wright agglutination test. The difference in the mean optical densities (OD) recorded by the new and the Vircell kits for patients and healthy individuals were tested using Two-tailed Student t-test. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the new kit were informed using Receiver operating curve analysis. The results were used to guide the choice of cutoff. Agreements in ODs recorded by the new and the Vircell kit was visually inspected using Bland-Altman plot.

RESULTS

The new I-ELISA showed excellent diagnostic performance (sensitivity and PPV = 95.7%, specificity and NPV = 97.8%) for the diagnosis of brucellosis. The cut-off area for the antibody index (AI) was determined to be 8-10, where AIs less than 8 and greater than 10 were considered Brucella-negative and -positive, respectively. AIs of 8-10 show equivocal results, requiring re-testing. The Vircell kit showed low (36.8%) sensitivity and perfect (100%) specificity on the same samples. The Bland-Altman plot showed low agreement between both tests in recording the OD values for the same individuals.

CONCLUSION

The new I-ELISA based on whole cell Brucella abortus S99 showed a good performance for the detection of Brucella spp. Lack of agreement between the new and the Vircell kit suggest that the performance of ELISA kits might be dependent on the geographical area under study. Hence, validation of the new and the Vircell kits is recommended prior to their implementation in other geographical areas.

Seroprevalence and risk factors of brucellosis among slaughtered indigenous cattle, abattoir personnel and pregnant women in Ngaoundéré, Cameroon

BACKGROUND

Brucellosis is a neglected debilitating zoonosis with a high prevalence in many developing countries. Bovine brucellosis is widespread in Cameroon but the epidemiological situation of human brucellosis is not known. A cross sectional study was carried to determine the seroprevalence and factors associated with bovine and human Brucellosis among abattoir personnel and pregnant women in Ngaoundéré, Cameroon.

METHODS

Serum sample from 590 abattoir cattle and 816 plausible occupational risk and vulnerable humans to brucellosis (107 abattoir personnel and 709 pregnant women) were collected and screened for anti-brucella antibodies using Rose Bengal Plate Test (RBPT) and ELISA tests. Structured questionnaires were used to collect data on socio-demographics and risk-factors. The differences in proportions between seropositive and seronegative reactors were tested using odds-ratio and χ2tests.

RESULTS

Bovine brucellosis seroprevalence was at 3.40% (n = 590; 3.4% for RBPT, 5.93% for i-ELISA). Human Brucella seroprevalence was at 5.6% among abattoir personnel (n = 107; 5.6% for RBPT, 12.15% for Brucella IgG ELISA) and 0.28% in pregnant women (n = 709; both tests). Breed (P < 0.00001) was associated with increased risk of brucellosis in cattle and the seroprevalence was highest among the Djafoun (OR = 16.67, 95%CI: 4.49-28.85) and Akou (OR = 16.96, 95% CI: 0.10-23.91) cattle compared to the other breeds. There was a moderate positive correlation (R2 = 0.5025) of Brucella IgG concentrations (> 200 U/ml) and clinical data for Brucella IgG ELISA seropositive humans. Several potential factors were associated (P > 0.05) with increased risk of human brucellosis seroprevalence among the abattoir personnel. The abattoir personnel were essentially males; the seropositive respondents were male and did not use protective equipment at work. Handling of foetus and uterine contents (OR = 13.00, 95%CI: 1.51-111.88) was associated with increased risk of human brucellosis.

CONCLUSIONS

Antibrucella antibodies are prevalent in cattle (3.40%), among abattoir personnel (5.60%) and in pregnant women (0.28%) in Ngaoundéré, Cameroon. The study reports the first evidence of human brucellosis in Cameroon and therefore, an indication of a real public health problem. Public awareness campaigns and health education especially among livestock professional and in agropastoral communities should be highlighted to disseminate knowledge, associated risk factors and control measures of brucellosis.

Cost-benefit analysis of intervention policies for prevention and control of brucellosis in India

Background

Brucellosis is endemic in the bovine population in India and causes a loss of US$ 3·4 billion to the livestock industry besides having a significant human health impact.

Methods

We developed a stochastic simulation model to estimate the impact of three alternative vaccination strategies on the prevalence of Brucella infection in the bovine populations in India for the next two decades: (a) annual mass vaccination only for the replacement calves and (b) vaccination of both the adult and young population at the beginning of the program followed by an annual vaccination of the replacement calves and, (c) annual mass vaccination of replacements for a decade followed by a decade of a test and slaughter strategy.

Findings

For all interventions, our results indicate that the prevalence of Brucella infection will drop below 2% in cattle and, below 3% in buffalo after 20 years of the implementation of a disease control program. For cattle, the Net Present Value (NPV) was found to be US $ 4·16 billion for intervention (a), US $ 8·31 billion for intervention (b) and, US $ 4·26 for intervention (c). For buffalo, the corresponding NPVs were US $ 8·77 billion, US $ 13·42 and, US $ 7·66, respectively. The benefit cost ratio (BCR) for the first, second and the third intervention for cattle were 7·98, 10·62 and, 3·16, respectively. Corresponding BCR estimates for buffalo were 17·81, 21·27 and, 3·79, respectively.

Conclusion

These results suggest that all interventions will be cost-effective with the intervention (b), i.e. the vaccination of replacements with mass vaccination at the beginning of the program, being the most cost-effective choice. Further, sensitivity analysis revealed that all interventions will be cost-effective even at the 50% of the current prevalence estimates. The results advocate for the implementation of a disease control program for brucellosis in India.

Brucellosis is an endemic zoonosis in India and recent studies demonstrate that the disease results in a median loss of US$ 3.43 billion in livestock populations. Lack of resources to compensate farmers and a ban on cow slaughter means that test and slaughter policy to control brucellosis cannot be implemented in India. This is the first systematic analysis of a brucellosis control program interventions for bovine brucellosis in India. The cost-benefit analysis was successfully conducted and indicated benefits of implementing the intervention policies. For each intervention, our results indicate that the prevalence of Brucella infection will drop below 2% in cattle after 20 years of the implementation of disease control program although some strategies were better than others. The expected net present value (NPV) was found to range from US $ 4·16 to $ 8·31 billion for cattle and from $ 7·66 to $ 13·42 billion in buffalo for the three strategies investigated. The benefit cost ratio (BCR) ranged from 3·16 to 10·62 for cattle and from 3·79 to 21·27 for buffalo. The results advocate for the implementation of a disease control program and will help development of an official health policy for the control of brucellosis in India.

A systematic review of current immunological tests for the diagnosis of cattle brucellosis

Brucellosis is a worldwide extended zoonosis with a heavy economic and public health impact. Cattle, sheep and goats are infected by smooth Brucella abortus and Brucella melitensis, and represent a common source of the human disease. Brucellosis diagnosis in these animals is largely based on detection of a specific immunoresponse. We review here the immunological tests used for the diagnosis of cattle brucellosis. First, we discuss how the diagnostic sensitivity (DSe) and specificity (DSp), balance should be adjusted for brucellosis diagnosis, and the difficulties that brucellosis tests specifically present for the estimation of DSe/DSp in frequentistic (gold standard) and Bayesian analyses. Then, we present a systematic review (PubMed, GoogleScholar and CABdirect) of works (154 out of 991; years 1960-August 2017) identified (by title and Abstract content) as DSe and DSp studies of smooth lipopolysaccharide, O-polysaccharide-core, native hapten and protein diagnostic tests. We summarize data of gold standard studies (n = 23) complying with strict inclusion and exclusion criteria with regards to test methodology and definition of the animals studied (infected and S19 or RB51 vaccinated cattle, and Brucella-free cattle affected or not by false positive serological reactions). We also discuss some studies (smooth lipopolysaccharide tests, protein antibody and delayed type hypersensitivity [skin] tests) that do not meet the criteria and yet fill some of the gaps in information. We review Bayesian studies (n = 5) and report that in most cases priors and assumptions on conditional dependence/independence are not coherent with the variable serological picture of the disease in different epidemiological scenarios and the bases (antigen, isotype and immunoglobulin properties involved) of brucellosis tests, practical experience and the results of gold standard studies. We conclude that very useful lipopolysaccharide (buffered plate antigen and indirect ELISA) and native hapten polysaccharide and soluble protein tests exist, provided they are applied taking into account the means available and the epidemiological contexts of this disease: i) mass vaccination; ii) elimination based on vaccination combined with test-and-slaughter; and iii) surveillance and existence of false positive serological reactions. We also conclude that the insistence in recent literature on the lack of usefulness of all smooth lipopolysaccharide or native hapten polysaccharide tests in areas where S19 vaccination is implemented is a misinterpretation that overlooks scientific and practical evidence.

Seroprevalence and Associated Risk Factors of Brucellosis among Indigenous Cattle in the Adamawa and North Regions of Cameroon

A cross-sectional seroprevalence study was conducted on cattle in the North and Adamawa Regions of Cameroon to investigate the status of bovine brucellosis and identify potential risk factors. The diagnosis was carried out using the Rose Bengal Plate test (RBPT) and indirect ELISA (i-ELISA), while questionnaires were used to evaluate risk factors for bovine brucellosis in cattle. The Bayesian approach was used to evaluate the diagnostic tests' sensitivity and specificity. The overall individual level (n = 1031) and herd level (n = 82) seroprevalence were 5.4% (0.4-10.5) and 25.6% (16.2-35.0), respectively. Bayesian analysis revealed sensitivity of 58.3% (26.4-92.7) and 89.6% (80.4-99.4) and specificity of 92.1% (88.7-95.2) and 95.7% (91.1-99.7) for RBPT and i-ELISA, respectively. Management related factors such as region, locality, herd size, and knowledge of brucellosis and animal related factors such as sex and age were significantly associated with seropositivity of brucellosis. Zoonotic brucellosis is a neglected disease in Cameroon. The study highlights the need for control measures and the need to raise public awareness of the zoonotic occurrence and transmission of bovine brucellosis in the country. An integrated disease control strategy mimicking the one health approach involving medical personnel, veterinarians, related stakeholders, and affected communities cannot be overemphasized.

Exploring the Diversity of Field Strains of Brucella abortus Biovar 3 Isolated in West Africa

Brucellosis is one of the most widespread bacterial zoonotic diseases in the world, affecting both humans and domestic and wild animals. Identification and biotyping of field strains of Brucella are of key importance for a better knowledge of the epidemiology of brucellosis, for identifying appropriate antigens, for managing disease outbreaks and for setting up efficient preventive and control programmes. Such data are required both at national and regional level to assess potential threats for public health. Highly discriminative genotyping methods such as the multiple locus variable number of tandem repeats analysis (MLVA) allow the comparison and assessment of genetic relatedness between field strains of Brucella within the same geographical area. In this study, MLVA biotyping data retrieved from the literature using a systematic review were compared using a clustering analysis and the Hunter-Gaston diversity index (HGDI). Thus, the analysis of the 42 MLVA genotyping results found in the literature on West Africa [i.e., from Ivory Coast (1), Niger (1), Nigeria (34), The Gambia (3), and Togo (3)] did not allow a complete assessment of the actual diversity among field strains of Brucella. However, it provided some preliminary indications on the co-existence of 25 distinct genotypes of Brucella abortus biovar 3 in this region with 19 genotypes from Nigeria, three from Togo and one from Ivory Coast, The Gambia, and Niger. The strong and urgent need for more sustainable molecular data on prevailing strains of Brucella in this sub-region of Africa and also on all susceptible species including humans is therefore highlighted. This remains a necessary stage to allow a comprehensive understanding of the relatedness between field strains of Brucella and the epidemiology of brucellosis within West Africa countries.

Low Seroprevalence of Brucellosis in Humans and Small Ruminants in the Gambia

Background

Brucellosis is a worldwide zoonosis with significant impact on rural livelihoods and a potentially underestimated contributor to febrile illnesses. The aim of this study was to estimate the seroprevalence of brucellosis in humans and small ruminants in The Gambia.

Methods

The study was carried out in rural and urban areas. In 12 rural villages in Kiang West district, sera were collected from humans (n = 599) and small ruminants (n = 623) from the same compounds. From lactating small ruminants, milk samples and vaginal swabs were obtained. At the urban study sites, sera were collected from small ruminants (n = 500) from slaughterhouses and livestock markets. Information on possible risk factors for seropositivity was collected through questionnaires. Sera were screened for antibodies against Brucella spp. with the Rose Bengal Test, ELISA and Micro Agglutination Test (human sera only). PCR was performed on 10 percent of the milk samples and vaginal swabs from small ruminants.

Results

One human and 14 sheep sera were positive by the Rose Bengal Test. The rest were negative in all serological tests used. The PCR results were all negative.

Conclusions

The results suggest that brucellosis is currently not a generalized problem in humans or small ruminants in The Gambia.

Bayesian Estimation of Sensitivity and Specificity of Rose Bengal, Complement Fixation, and Indirect ELISA Tests for the Diagnosis of Bovine Brucellosis in Ethiopia

Test evaluation in the absence of a gold standard test was conducted for the diagnosis and screening of bovine brucellosis using three commercially available tests including RBPT, CFT, and I-ELISA in National Animal Health Diagnostic and Investigation Center (NAHDIC) Ethiopia. A total of 278 sera samples from five dairy herds were collected and tested. Each serum sample was subjected to the three tests and the results obtained were recorded and the test outcomes were cross-classified to estimate the sensitivity and specificity of the tests using Bayesian model. Prior information generated on the sensitivity and specificity of bovine brucellosis from published data was used in the model. The three test-one population Bayesian model was modified and applied using WinBug software with the assumption that the dairy herds have similar management system and unknown disease status. The Bayesian posterior estimate for sensitivity was 89.6 (95% PI: 79.9-95.8), 96.8 (95% PI: 92.3-99.1), and 94 (95% PI: 87.8-97.5) and for specificity was 84.5 (95% PI: 68-94.98), 96.3 (95% PI: 91.7-98.8), and 88.5 (95% PI: 81-93.8) for RBT, I-ELISA, and CFT, respectively. In this study I-ELISA was found with the best sensitivity and specificity estimates 96.8 (95% PI: 92.3-99.1) and 96.3 (95% PI: 91.7-98.8), compared to both CFT and RBPT.

Evaluation of three competitive ELISAs and a fluorescence polarisation assay for the diagnosis of bovine brucellosis

Bovine brucellosis is an infectious disease of worldwide public health and economic importance. The usual tests for the diagnosis of this disease include the Rose-Bengal test (RBT), complement fixation test (CFT), serum agglutination test (SAT) and indirect ELISA. New tests such as competitive ELISAs (C-ELISA) and fluorescence polarisation assay (FPA) have been developed. However, C-ELISA may correspond to different protocols and a wide variation may exist in their diagnostic performance. The aim of this study was to evaluate three commercially available C-ELISA kits (C-ELISA1-3) and FPA for the diagnosis of bovine brucellosis and compare test performance with RBT, CFT, indirect ELISA and FPA. Sera submitted to EU laboratories in 2011 from 5111 adult cattle were tested. Individual test sensitivities (Se) and specificities (Sp) were estimated. Threshold assessment using the receiver operating characteristic method was also performed. The most sensitive tests were FPA (99.0%; 95% confidence interval [CI], 97.9-100%), C-ELISA1 (98.4%; 95% CI, 97.0-99.8%) and RBT (97.7%; 95% CI, 95.9-99.3%). The most specific tests were CFT (99.98%; 95% CI, 99.93-100%), SAT (99.98%; 95% CI, 99.93-100%) and RBT (99.89%; 95% CI, 99.79-99.99%). Among the new tests, none of the three C-ELISA kits studied could be recommended as a single screening test because of their low specificity, especially when used in a herd. C-ELISA3 could not be recommended as confirmatory test on individual animals to determine whether false positive serological test results had occurred.

Latent class regression models for simultaneously estimating test accuracy, true prevalence and risk factors for Brucella abortus

In 2003/2004 a field trial was conducted in Northern Ireland to assess the diagnostic accuracy of six serological tests for bovine brucellosis caused by Brucella abortus. Whereas between-test comparisons have been used to calculate test performances so far, the present study used a latent class approach to estimate diagnostic test accuracy parameters in the absence of a gold standard for these six tests simultaneously and to estimate the true prevalence, while accounting for clustering in the study population and risk factors for true prevalence. Results obtained in this study with regard to prevalence, sensitivity and specificity were largely in accordance with previous findings. Screening tests (SAT and EDTA) appeared to be the most sensitive; however, at low prevalences the EDTA and CFT showed the highest positive predictive values of all investigated tests. The specificities and negative predictive values of all diagnostic tests were found to be very high. Differences of prevalence between three groups of the study population with different risk of exposure could be attributed to the mode of sampling indicating that a more risk-based sampling will result in a higher prevalence than a cross-sectional sampling mode. Age, dairy status and history of abortion were shown to influence the prediction of the latent true infection status.

Inter-laboratory evaluation of the performance parameters of a Lateral Flow Test device for the detection of Bluetongue virus-specific antibodies

Bluetongue (BT) is a viral vector-borne disease affecting domestic and wild ruminants worldwide. In this study, a commercial rapid immuno-chromatographic method or Lateral Flow Test (LFT) device, for the detection of BT virus-specific antibodies in animal serum, was evaluated in an international inter-laboratory proficiency test. The evaluation was done with sera samples of variable background (ruminant species, serotype, field samples, experimental infections, vaccinated animals). The diagnostic sensitivity was 100% (95% C.I. [90.5-100]) and the diagnostic specificity was 95.2% (95% C.I. [76.2-99.9]). The repeatability (accordance) and reproducibility (concordance) were 100% for seropositive samples but were lower for two of the seronegative samples (45% and 89% respectively). The analytical sensitivity, evaluated by testing positive sera at increasing dilutions was better for the BT LFT compared to some commercial ELISAs. Seroconversion of an infected sheep was detected at 4 days post infection. Analytical specificity was impaired by cross-reactions observed with some of the samples seropositive for Epizootic Haemorrhagic Disease Virus (EHDV). The agreement (Cohen's kappa) between the LFT and a commercial BT competitive ELISA was 0.79 (95% CI [0.62-0.95]). Based on these results, it can be concluded that the BT LFT device is a rapid and sensitive first-line serological test that can be used in the field, especially in areas endemic for the disease where there is a lack of diagnostic facilities.

The Prevalence of Brucellosis in Cattle, Goats and Humans in Rural Uganda: A Comparative Study

A cross-sectional study was conducted to determine the presence of brucellosis in cattle, goats and humans in farms from south-western Uganda and identify risk factors associated with brucellosis in these three host groups. Data and serum samples were collected from 768 cattle, 315 goats and 236 humans, with 635 samples of bovine milk, from 70 farms in two different study areas in south-western Uganda. Sera from livestock were tested with the Rose Bengal Plate test, using B. abortus and B. melitensis antigens, and human sera were tested with a commercial IgG/IgM lateral flow assay. Milk samples were tested using the OIE-approved milk ring test. Screening tests for brucellosis were positive in 14% of cattle serum, 29% of bovine milk, 17% of goat serum and 11% of human serum samples. There were significant differences in the test prevalence of brucellosis by study site, with levels higher in the study area near Lake Mburo National Park than in the study area near Queen Elizabeth National Park. Multivariable regression models identified risk factors associated with increasing test positivity at the individual and farm levels for cattle, goats and humans. Positive associations were seen between increasing seropositivity of brucellosis in goats, cattle and humans. Results of multivariable analyses suggest that improvements in farm biosecurity and hygiene may reduce the risk of brucellosis on the farm and suggest a role for ticks in bovine brucellosis. Although cattle are the focus of brucellosis control in Uganda, the significant associations between seropositivity in humans and seropositivity in goats suggest that brucellosis in goats may be an important contributor to the epidemiology of the disease on the farm.