Enzyme immunoassay for the diagnosis of brucellosis: chimeric Protein A–Protein G as a common enzyme labeled detection reagent for sera for different animal species

Using serosurveys to optimize surveillance for zoonotic pathogens

Zoonotic pathogens pose a significant risk to human health, with spillover into human populations contributing to chronic disease, sporadic epidemics, and occasional pandemics. Despite the widely recognized burden of zoonotic spillover, our ability to identify which animal populations serve as primary reservoirs for these pathogens remains incomplete. This challenge is compounded when prevalence reaches detectable levels only at specific times of year. In these cases, statistical models designed to predict the timing of peak prevalence could guide field sampling for active infections. Thus, we develop a general model that leverages routinely collected serosurveillance data to optimize sampling for elusive pathogens by predicting time windows of peak prevalence. Using simulated data sets, we show that our methodology reliably identifies times when pathogen prevalence is expected to peak. Then, we demonstrate an implementation of our method using publicly available data from two putative Ebolavirus reservoirs, straw-colored fruit bats (Eidolon helvum) and hammer-headed bats (Hypsignathus monstrosus). We envision our method being used to guide the planning of field sampling to maximize the probability of detecting active infections, and in cases when longitudinal data is available, our method can also yield predictions for the times of year that are most likely to produce future spillover events. The generality and simplicity of our methodology make it broadly applicable to a wide range of putative reservoir species where seasonal patterns of birth lead to predictable, but potentially short-lived, pulses of pathogen prevalence.

Qiviut cortisol is associated with metrics of health and other intrinsic and extrinsic factors in wild muskoxen (Ovibos moschatus)

Glucocorticoid (GC) levels are increasingly and widely used as biomarkers of hypothalamic-pituitary-adrenal (HPA) axis activity to study the effects of environmental changes and other perturbations on wildlife individuals and populations. However, identifying the intrinsic and extrinsic factors that influence GC levels is a key step in endocrinology studies to ensure accurate interpretation of GC responses. In muskoxen, qiviut (fine woolly undercoat hair) cortisol concentration is an integrative biomarker of HPA axis activity over the course of the hair's growth. We gathered data from 219 wild muskoxen harvested in the Canadian Arctic between October 2015 and May 2019. We examined the relationship between qiviut cortisol and various intrinsic (sex, age, body condition and incisor breakage) and extrinsic biotic factors (lungworm and gastrointestinal parasite infections and exposure to bacteria), as well as broader non-specific landscape and temporal features (geographical location, season and year). A Bayesian approach, which allows for the joint estimation of missing values in the data and model parameters estimates, was applied for the statistical analyses. The main findings include the following: (i) higher qiviut cortisol levels in males than in females; (ii) inter-annual variations; (iii) higher qiviut cortisol levels in a declining population compared to a stable population; (iv) a negative association between qiviut cortisol and marrow fat percentage; (v) a relationship between qiviut cortisol and the infection intensity of the lungworm Umingmakstrongylus pallikuukensis, which varied depending on the geographical location; and (vi) no association between qiviut cortisol and other pathogen exposure/infection intensity metrics. This study confirmed and further identified important sources of variability in qiviut cortisol levels, while providing important insights on the relationship between GC levels and pathogen exposure/infection intensity. Results support the use of qiviut cortisol as a tool to monitor temporal changes in HPA axis activity at a population level and to inform management and conservation actions.

Superantigen Recognition and Interactions: Functions, Mechanisms and Applications

Superantigens are unconventional antigens which recognise immune receptors outside their usual recognition sites e.g. complementary determining regions (CDRs), to elicit a response within the target cell. T-cell superantigens crosslink T-cell receptors and MHC Class II molecules on antigen-presenting cells, leading to lymphocyte recruitment, induction of cytokine storms and T-cell anergy or apoptosis among many other effects. B-cell superantigens, on the other hand, bind immunoglobulins on B-cells, affecting opsonisation, IgG-mediated phagocytosis, and driving apoptosis. Here, through a review of the structural basis for recognition of immune receptors by superantigens, we show that their binding interfaces share specific physicochemical characteristics when compared with other protein-protein interaction complexes. Given that antibody-binding superantigens have been exploited extensively in industrial antibody purification, these observations could facilitate further protein engineering to optimize the use of superantigens in this and other areas of biotechnology.

Improving the diagnosis of bovine tuberculosis using gold nanoparticles conjugated with purified protein derivative: special regard to staphylococcal protein A and streptococcal protein G

Different ancillary immunodiagnostic tests were traditionally-established for diagnosis of bovine tuberculosis (BTB) either cellular or humoral as tuberculin skin test (TST), gamma interferon (INF-γ), and indirect enzyme-linked immunosorbent assay (iELISA). These tests had been consumed more time and expensive, and needed sophisticated equipment. To dissolve these problems, serological diagnosis depending on humoral immunity is the aim of this work. Herein, slide-based agglutination test was chosen as a rapid and simple field test based on purified protein derivative (PPD) antigen in addition to some supplementation materials such as Staphylococcal protein A (SPA) and Streptococcal protein G (SPG) to improve detection of BTB antibody in serum samples. Gold nanoparticles (Au NPs) were synthesized by gamma ray, and after complete characterization, the synthesized Au NPs were spherical, small-sized, and stable without any impurities. Addition of such supplementation reagents for serodiagnosis of tuberculosis is of paramount important for the detection of serum antibodies against tuberculosis (TB) and it was considered an easily simple and possible way for improving TB diagnosis. In this work, 70 animals tested positive for TST as well as 20 animals tested negative for TST were used for the diagnosis of BTB depending on humoral immune response based on PPD slide agglutination test using reporter regents (SPA and/or SPG) either native or recombinant. The agglutination density was recorded and read in 4 degrees of positivity with scores ranging from negative (-) to very strong reaction (++++) occurred in different times of agglutination. Groups showed 100% positive reactivates employed in Exp. 1, 2, and 3 with differentiation of slide agglutination test density and was rated from moderate positivity (2+) to very strong (4+), with predominant positivity in density of (3+). Pink-colored intensity is associated with the strengthened reactions between PPD-conjugated Au NPs and serum antibody of each tested samples, which allows for visual rapid, simple, and effective attractive diagnosis of BTB. The specificity and sensitivity of the serological tests were characterized. TST offers the highest sensitivity (83.6%) among the other immunoassays, while the lowest specificity was recorded in TST (57.4%). SPA/SPG offers the best performance in term of combined sensitivity and specificity (performance index) of 175.4. Therefore, the development and uses of detection reagent (such as SPA and/or SPG) slide co-agglutination test (COAT), either native or recombinant (rSPA/SPG) for the detection of TB antibodies based on PPD antigen, as well as the uses of Au NPs rSPA/SPG as detection conjugate based on the same antigen, were also performed as a simple, rapid, sensitive, specific, eco-friendly, and low cost, which shows a great potential in field and lab diagnosis of BTB. So, high reduction in reagents that yields reactions similarly as traditional techniques was needed.

Detecting total immunoglobulins in diverse animal species with a novel split enzymatic assay

BACKGROUND

Total immunolobulin G concentration is a useful, albeit underutilized, diagnostic parameter for health assessments of non-domestic animal species, due to a lack of functional diagnostic tools. Traditional assays, including enzyme-linked immunosorbent assay or radial immunodiffusion, require development of specific reagents (e.g., polyclonal antisera and appropriate protocols) for each animal species, precluding wide and easy adoption in wildlife welfare. As an alternative, bacterial virulence factors able to bind IgGs in antigen-independent manner can be used. To further simplify the diagnostic procedure and increase the number of species recognized by an assay, in this study a recently developed Split Trehalase immunoglobulin assay (STIGA) with bIBPs as a sensing elements was used to detect antibodies in 29 species from 9 orders. Three bacterial immunoglobulin binding proteins (protein G, protein A and protein L) were incorporated into STIGA reagents to increase the number of species recognized.

RESULTS

IgG concentrations were detected through glucose production and produced signals were categorized in 4 categories, from not active to strong signal. Activation was detected in almost all tested animal species, apart from birds. Incorporation of Protein G, Protein A and Protein L allowed detection of IgGs in 62, 15.5 and 6.9% of species with a strong signal, respectively. Assays combining 2 bacterial immunoglobulin binding proteins as sensing element generally gave poorer performance than assays with the same bacterial immunoglobulin binding proteins fused to both trehalase fragments.

CONCLUSIONS

STIGA assays have potential to be further developed into an easily adoptable diagnostic test for total amount of IgGs in almost any serum sample, independent of species.

A comprehensive review on staphylococcal protein A (SpA): Its production and applications

The Staphylococcus aureus protein A (SpA) can be obtained through the culture of wild-type S. aureus and also as a recombinant protein in safe bacterial hosts. Several methods have been used to purify SpA among which ion-exchange chromatography, affinity chromatography, gel filtration, and per aqueous liquid chromatography (PALC) are common. SpA has a wide range of biochemical, biotechnological, and medical applications and is most commonly used in test methods such as immunoprecipitation, enzyme-linked immunosorbent assay, and Western blotting. SpA has also been widely utilized in pharmaceutical applications to bind to immune complexes and serum immunoglobulins. SpA also directly binds to the B-cells preventing initiation of infectious diseases as well as having a role in the development of various autoimmune diseases. This review considers different applications of SpA in biotechnology and its novel clinical application for effective treatment of autoimmune diseases. It also discusses various strategies for expression and purification of the SpA including types of column chromatography that are commonly used in protein purification and developing SpA surface display technologies. Finally, this review highlights the potential and novel applications of SpA immobilization, SpA typing, protein engineering for further development of immunological and biochemical research, and also application of SpA as a diagnostic biosensor.

Evaluation of two rapid immunochromatographic tests for diagnosis of brucellosis infection in cattle

Brucellosis is a serious infectious disease that causes significant economic losses in the livestock industry. Its early diagnosis allows an adequate disease control in cattle. DAVIH Laboratories designed a lateral flow immunochromatographic assay using protein A-colloidal gold as a detector reagent (LFIA-PA). The objective of this work was to compare the performance of this assay using protein G-colloidal gold (LFIA-PG) with its performance using protein A-colloidal gold as the detector reagent. The assays were carried out with 20 μL of serum and 130 μL of running buffer. Interpretation of bands was by visual inspection with the naked eye at 15- 20 minutes after sample application. The tests were evaluated with 449 samples of bovine serum (111 positive and 338 negative). The diagnostic sensitivity and specificity, the positive and negative predictive values, and the efficacy of both assays were calculated, and their concordance was estimated by calculating the kappa (k) index. The estimated values of the parameters for LFIA-PG and LFPIA-PA were 100% and 95.2% of diagnostic sensitivity, 96.2% and 97.3% of diagnostic specificity, 89.5% and 92.3% for the positive predictive value, 100% and 98.5% for the negative predictive value, and 97.1% and 96.89% of efficacy, respectively. The concordance between both tests was very good (k = 0.95). It was shown the possibilities of developing a system with LFIA-PG capable of detecting antibodies against Brucella spp. The performance of the test makes possible its use as a screening method in the diagnosis of brucellosis.

Serosurveillance for pandemic influenza A (H1N1) 2009 virus infection in domestic elephants, Thailand

The present study conducted serosurveillance for the presence of antibody to pandemic influenza A (H1N1) 2009 virus (H1N1pdm virus) in archival serum samples collected between 2009 and 2013 from 317 domestic elephants living in 19 provinces situated in various parts of Thailand.

To obtain the most accurate data, hemagglutination-inhibition (HI) assay was employed as the screening test; and sera with HI antibody titers ≥20 were further confirmed by other methods, including cytopathic effect/hemagglutination based-microneutralization (microNT) and Western blot (WB) assays using H1N1pdm matrix 1 (M1) or hemagglutinin (HA) recombinant protein as the test antigen. Conclusively, the appropriate assays using HI in conjunction with WB assays for HA antibody revealed an overall seropositive rate of 8.5% (27 of 317). The prevalence of antibody to H1N1pdm virus was 2% (4/172) in 2009, 32% (17/53) in 2010, 9% (2/22) in 2011, 12% (1/8) in 2012, and 5% (3/62) in 2013. Notably, these positive serum samples were collected from elephants living in 7 tourist provinces of Thailand. The highest seropositive rate was obtained from elephants in Phuket, a popular tourist beach city. Young elephants had higher seropositive rate than older elephants.

The source of H1N1pdm viral infection in these elephants was not explored, but most likely came from close contact with the infected mahouts or from the infected tourists who engaged in activities such as elephant riding and feeding. Nevertheless, it could not be excluded that elephant-to-elephant transmission did occur.

Recent advances in Brucella abortus vaccines

Brucella abortus vaccines play a central role in bovine brucellosis control/eradication programs and have been successfully used worldwide for decades. Strain 19 and RB51 are the approved B. abortus vaccines strains most commonly used to protect cattle against infection and abortion. However, due to some drawbacks shown by these vaccines much effort has been undertaken for the development of new vaccines, safer and more effective, that could also be used in other susceptible species of animals. In this paper, we present a review of the main aspects of the vaccines that have been used in the brucellosis control over the years and the current research advances in the development of new B. abortus vaccines.

A protein A/G indirect enzyme-linked immunosorbent assay for the detection of anti-Brucella antibodies in Arctic wildlife

A species-independent indirect enzyme-linked immunosorbent assay (iELISA) based on chimeric protein A/G was established for the detection of anti-Brucella antibodies in Arctic wildlife species and compared to previously established brucellosis serological tests for hooded seals (Cystophora cristata), minke whales (Balaenoptera acutorostrata), sei whales (Balaenoptera borealis), fin whales (Balaenoptera physalus), and polar bears (Ursus maritimus), as well as bacteriology results for reindeer and caribou (Rangifer tarandus sp.). The protein A/G iELISA results were consistent with the other serological tests with Cohen kappa values between 0.47 and 0.92, and the protein A/G iELISA can thus offer a technically simple method for these species yielding results consistent with established brucellosis serological tests. Receiver operator characteristics analysis proved that the reindeer and caribou protein A/G iELISA results were consistent with the bacteriological gold standard with an area under the curve of 0.99, and the protein A/G iELISA was thus validated as a sensitive and specific serological method for the detection of anti-Brucella antibodies in reindeer and caribou. The binding of the antibodies from the respective species to protein A and G were also evaluated in the iELISA. The antibodies from hooded seals and polar bears reacted stronger to protein A than to G. The sei whale, fin whale, reindeer, and caribou antibodies reacted stronger to protein G than to A. The minke whale antibodies reacted to both protein A and G. There was a strong correlation (r s = 0.88-0.98) between the optical density results obtained with the iELISA with protein A/G and protein A or G, showing that protein A/G is as well suited as protein A or G for the detection of anti-Brucella antibodies in these species with the iELISA.

Improvement in the diagnosis of Brucella abortus infections in naturally infected water buffaloes (Bubalus bubalis) using an ELISA with a Protein-G-based indicator system

Brucellosis caused by Brucella abortus in domestic water buffaloes (Bubalus bubalis) raised under the traditional system of husbandry in northern India was diagnosed using an enzyme-linked immunosorbent assays (ELISA) with a Protein-G-based indicator system (Protein-G ELISA). A total of 1,551 animals that are positive (N = 61), negative (N = 243), and suspected (N = 1,247) for brucellosis were examined. Rose bengal test (RBT) was used to predict the disease, and accordingly, animals were dichotomized in positive and negative population for receiver operating characteristic (ROC) curve analysis to determine the sensitivity, the specificity, and the performance index of Protein-G ELISA. Taking all animals (N = 1551) into account, the ROC curve analysis revealed cut off value of 29.6% positivity (%P) with 98.40% and 94.94%, sensitivity and specificity, respectively. The results were compared with ELISA in which anti-bovine conjugate was used. The cut off in ELISA was 37.9%P and sensitivity and specificity were 96.26% and 97.07%, respectively. The performance indexes of both the assays were almost equal and were 193.34 for Protein-G ELISA and 193.33 for ELISA. The cut off values of both the tests changed, if only known positive (N = 61) and known negative (N = 243) animals were used for ROC curve analysis, and accordingly, changes in sensitivity and specificity were observed with significant decrease of performance indexes of both the tests. The high optical density (P < 0.0001) background signal with negative serum control and high %P (P < 0.0001) in sera from negative population were noticed in ELISA in comparison to Protein-G ELISA.

Universal indirect enzyme-linked immunosorbent assay for monitoring of human and animal brucellosis in Kazakhstan

Combinations of conventional serological methods and new ELISA procedures were evaluated to develop the most efficient and effective diagnostics for the detection of brucellosis in humans and animals. Sera from humans (n=249) and animals (n=99) were collected from brucellosis endemic areas (Zhambyl district and Enbekshi-Kazakh district of Almaty region in Kazakhstan) for serologic analysis. Sera from the humans reacted positively in the RBT (38.5%), SAT (43.3%), iELISA (42.5%) while sera from the animals reacted positively in RBT (79.8%), SAT (89.9%), CF (87.8%), iELISA (100%). Greater seropositivity was detected in animals as compared to human samples. All positive sera were also evaluated on an indirect ELISA (iELISA). Bacterial isolation was attempted on seropositive human sera. Our data indicate that the combination of conventional serological tests (SAT and CF), combined with the iELISA is optimal for the processing of large numbers of samples and the most efficient detection of human and animal brucellosis.

Spatial distribution and risk factors of Brucellosis in Iberian wild ungulates

Background

The role of wildlife as a brucellosis reservoir for humans and domestic livestock remains to be properly established. The aim of this work was to determine the aetiology, apparent prevalence, spatial distribution and risk factors for brucellosis transmission in several Iberian wild ungulates.

Methods

A multi-species indirect immunosorbent assay (iELISA) using Brucella S-LPS antigen was developed. In several regions having brucellosis in livestock, individual serum samples were taken between 1999 and 2009 from 2,579 wild bovids, 6,448 wild cervids and4,454 Eurasian wild boar (Sus scrofa), and tested to assess brucellosis apparent prevalence. Strains isolated from wild boar were characterized to identify the presence of markers shared with the strains isolated from domestic pigs.

Results

Mean apparent prevalence below 0.5% was identified in chamois (Rupicapra pyrenaica), Iberian wild goat (Capra pyrenaica), and red deer (Cervus elaphus). Roe deer (Capreolus capreolus), fallow deer (Dama dama), mouflon (Ovis aries) and Barbary sheep (Ammotragus lervia) tested were seronegative. Only one red deer and one Iberian wild goat resulted positive in culture, isolating B. abortus biovar 1 and B. melitensis biovar 1, respectively. Apparent prevalence in wild boar ranged from 25% to 46% in the different regions studied, with the highest figures detected in South-Central Spain. The probability of wild boar being positive in the iELISA was also affected by age, age-by-sex interaction, sampling month, and the density of outdoor domestic pigs. A total of 104 bacterial isolates were obtained from wild boar, being all identified as B. suis biovar 2. DNA polymorphisms were similar to those found in domestic pigs.

Conclusions

In conclusion, brucellosis in wild boar is widespread in the Iberian Peninsula, thus representing an important threat for domestic pigs. By contrast, wild ruminants were not identified as a significant brucellosis reservoir for livestock.

Evaluation of indirect enzyme-linked immunosorbent assays and IgG avidity assays using a protein A-peroxidase conjugate for serological distinction between Brucella abortus S19-vaccinated and -infected cows

This study aimed to evaluate the use of protein A-peroxidase (horseradish peroxidase [HRPO]) in indirect enzyme-linked immunosorbent assays (iELISAs) and IgG avidity assays for serological distinction between Brucella abortus S19-vaccinated and -infected cows. Four groups were analyzed: GI, 41 nonvaccinated seropositive cows; GII, 79 S19-vaccinated heifers analyzed at 3 months postvaccination; GIII, 105 S19-vaccinated cows analyzed after 24 months of age; and GIV, 278 nonvaccinated seronegative cows. IgG levels and avidity to B. abortus smooth lipopolysaccharide (S-LPS) were determined using anti-bovine IgG-HRPO or protein A-HRPO conjugates. Similar levels of IgG anti-S-LPS were found with GI using both conjugates. Lower IgG levels were detected with GII, GIII, and GIV using protein A-HRPO. Both conjugates showed high performance in discriminating GI from GIII, with high sensitivity (Se; 97.6%) and specificity (Sp; 97.1%). Protein A-HRPO was better in distinguishing GI from GIV (Se, 97.6%; Sp, 94.6%) and GI from GII (Se, 80.5%; Sp, 94.9%). Protein A-HRPO excluded a higher number of positive samples with GII and GIV. IgG avidity showed that protein A-HRPO, but not anti-IgG-HRPO, was able to distinguish nonvaccinated from vaccinated cattle, showing a higher avidity index (AI) with GI than with GII, with 78% of serum samples in GII showing an AI of <50%. Therefore, the iELISA using B. abortus S-LPS antigen and protein A-HRPO conjugate for preferential detection of the IgG2 subclass was shown to be suitable for serological distinction between S19-vaccinated and -infected cows. Also, antibodies generated after vaccination showed lower avidity, suggesting a role for the IgG2 subclass as an antibody of higher-affinity maturation after infection, constituting an additional tool for differentiating vaccinated from infected cattle.

Rapid, field-adapted indirect enzyme-linked immunosorbent assay for detection of antibodies in bovine whole blood and serum to Brucella abortus

A simple, rapid, field-adapted indirect enzyme-linked immunoassay (FldELISA) for the detection of antibodies to Brucella abortus in whole blood and serum has been developed. This assay detects antibodies to B. abortus in approximately 15 min or less. Over a 3-month period, this assay has consistently identified immunized and nonimmunized animals, while the percent coefficient of variation for each immunized animal has been less than 20%. As with any indirect enzyme-linked immunoassay, quality control can be established and maintained. Using defined positive and negative sera, the sensitivity and specificity of the FldELISA was 100% and 94.2%, respectively. As a model, this test can be readily extended to other disease applications that use lipopolysaccharide or other stable antigens for the detection of antibodies, such as those to Salmonella spp., Escherichia coli, or Yersinia spp.

Efficacy of protein A-HRP in an immunological study of black rockfish (Sebastes schlegeli Higendorf) humoral immune responses

The efficacy of protein A-horse radish peroxidase (HRP), as compared to that of mouse polyclonal antibody raised against purified Ig, in detection of black rockfish (Sebastes schlegeli Higendorf) immunoglobulin (Ig) was examined. Protein A affinity chromatography successfully purified Ig from black rockfish serum; the purified-Ig could be visualised as two protein bands (MW 70 and 25kDa) following resolution with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions. In SDS-PAGE immunoblot profiles of the purified-Ig, the mouse polyclonal antibody recognised both the light chain and heavy chains of rockfish Ig, whereas protein A-HRP immunostained only the heavy chain of rockfish Ig. These results suggest that protein A-HRP may be used to detect rockfish antibody-antigen complexes in immunoassays. In a 2-DE immunoblot assay for exploring antigenic profiles of Lactococcus garvieae KG9408, protein A-HRP successfully detected specific antibodies to antigenic proteins of L. garvieae in the rockfish Ig. In addition, enzyme linked immunosorbent assay (ELISA) showed a high correlation between the results obtained for positivity of L. garvieae when protein A-HRP and the mouse polyclonal antibody-was used to analyse samples from 25 diseased rockfish. These results collectively indicate that protein A-HRP has a high affinity for Ig, and may be useful for new investigations into the humoral immune responses of rockfish.

Unusual clinical presentation of brucellosis caused by Brucella canis

Brucella canis is considered a rare cause of human brucellosis. The clinical importance of this infection may have been underestimated so far because of difficulties with presumptive diagnosis. The case described here presented symptoms compatible with brucellosis but the routine tests using Brucella abortus antigen were negative. The infection would have remained undiagnosed if culture had not been positive. This case illustrates the potential for a favourable outcome in Brucella canis diagnosis and supports recommendations for the use of B. canis serology. The infection should be suspected in patients with compatible symptoms and negative serology for B. abortus antigen.

Use of Brucella canis antigen for detection of ovine serum antibodies against Brucella ovis

Brucella ovis causes a genital disease of sheep manifested by epididymitis in rams and placentitis in ewes producing reduced fertility in the flock. Clinical diagnosis is not sensitive enough and bacteriological testing is not feasible for detection of the disease in large numbers of animals. Indirect methods of serological testing are preferred for routine diagnosis, of which agar gel immunodiffusion (AGID), complement fixation (CF) and ELISA tests are recommended as the most efficient. Since B. ovis shares antigenic components with Brucella canis, it would seem that either strain could be used as antigen with the same results; however, the advantage of the B. canis (M-) strain variant is that it can be used to develop a satisfactory antigen for agglutination tests. We present data on AGID and IELISA tests using B. ovis antigen and rapid screening agglutination test (RSAT), 2-mercapto-ethanol RSAT (2ME-RSAT) and IELISA using B. canis antigen. We tested 225 animals. The cut-off values were adjusted by ROC analysis using 51 negative and 32 positive sera; the IELISA-B. canis cut-off value was 39 (%P) and IELISA-B. ovis, 51 (%P), with 100% sensitivity and specificity. Of the 32 positive sera from the infected flock RSAT detected 32 (100%), 2ME-RSAT 29 (91%) and AGID 31 (97%). Of the 142 sera from suspicious flocks, 46 were negative and 56 positive in all the tests; 16 were positive by RSAT, IELISA-B. canis and IELISA-B. ovis, 20 positive only with RSAT and 2 positive only by both IELISAs. RSAT is a very sensitive screening test that, because of its simplicity and easy interpretation, following a study in larger sample, could replace AGID as a screening test for diagnosis of ovine brucellosis caused by B. ovis. The IELISA-B. canis or IELISA-B. ovis could be used as confirmatory tests, since they show equal specificity and sensitivity.