Validation of FPA and cELISA for the detection of antibodies to Brucella abortus in cattle sera and comparison to SAT, CFT, and iELISA

Evaluation of a fluorescence polarization assay for the detection of serum antibodies to Brucella abortus in water buffalo (Bubalus bubalis)

The fluorescence polarization assay (FPA) was evaluated for the serological diagnosis of brucellosis in water buffalo (Bubalus bubalis) in southern Italy. This assay uses O-polysaccharide prepared from Brucella abortus lipopolysaccharide conjugated with fluorescein isothiocyanate as a tracer. It has many methodological advantages over older, more established tests and can be performed in a fraction of the time. Sera from 890 buffalos from the Campania Region - 526 positive sera and 364 negative sera according to the complement fixation test (CFT) - were evaluated in this study. All samples were tested with the Rose Bengal test (RBT), CFT, and FPA in parallel and in blind fashion. Sensitivities (Sn) were 84.5% and 92.6%, and specificities (Sp) were 93.1% and 91.2% for RBT and FPA, respectively, relative to CFT. Finally, receiver operating characteristic (ROC) analysis suggested a cut-off value of 117 millipolarization (mP) units. On the whole, these results suggested that FPA might replace RBT in the diagnosis of buffalo brucellosis for its better performance relative to CFT, its adjustable cut-off useful in different epidemiological situations, its reliability, ease of performance, and for its potential application in field and high-throughput laboratories.

Seroepidemiological investigation of brucellosis in sheep abortions in Kars, Turkey

This study was undertaken to investigate the seroprevalence of brucellosis in unvaccinated sheep from the flocks having previous abortion cases in Kars and around, Turkey and to compare the efficacy of each serological test used. Four hundred serum samples collected from 16 different flocks of sheep having a history of abortions in Kars and its surrounding area in Turkey were examined for the presence of antibodies raised against Brucella using Rose Bengal Plate Test (RBPT), Serum Agglutination Test (SAT), Rivanol Agglutination Test (RAT) and Complement Fixation Test (CFT). All animals were unvaccinated against Brucella. Of the serum samples tested, 147 (%36.7), 142 (%35.5), 139 (%34.75) and 135 (%33.75) were found positive by SAT, RAT, RBPT and CFT, respectively. No statistically significant difference was found between the serological tests used (p > 0.05). It is concluded from this study that brucellosis continues to be an important problem for ovine abortions and poses a risk both for human and other animals in this area. Therefore, adequate intervention measures should be implemented to control and eradicate brucellosis. In addition, if conventional serological tests are used at least two tests, RPBT for screening and CFT for the confirmation of the positive samples are preferable, should be used in parallel for detection of brucellosis effectively.

Validation of a second generation competitive enzyme immunoassay (CELISA) for the diagnosis of brucellosis in various species of domestic animals

A second generation competitive enzyme immunoassay (CELISA) for detection of bovine antibody to Brucella abortus was developed to eliminate reagent variables in the assay. This assay was different from earlier CELISA formats in that it used recombinant protein A and protein G immunoglobulin receptors (PAG), labelled with horseradish peroxidase, thus eliminating the requirement for polyclonal anti-mouse-enzyme conjugate for detection. This allowed standardization of the assay. The CELISA uses a monoclonal antibody specific for a common epitope of the O-polysaccharide (OPS) of smooth lipopolysaccharide (SLPS) derived from B. abortus S1119.3. This antibody did not react with PAG. This monoclonal antibody was used to compete with antibody in the bovine test serum to the smooth lipopolysaccharide (SLPS) antigen. Reaction of bovine antibody was then measured directly with the PAG enzyme conjugate. In this case, development of colour in the reaction indicated a positive reaction. The performance characteristics of the new CELISA, sensitivity, specificity and exclusion of antibody of B. abortus S19 vaccinated animals, were very similar to those of the classical CELISA and to the indirect enzyme immunoassay (IELISA) when using sera deemed positive by isolation of the bacterium, either from individual animals or from some animals on the premises. All sera were tested by the buffered antigen plate agglutination test (BPAT) and the complement fixation test (CFT). Only samples positive on both BPAT and CFT were considered as positive and only samples negative on both tests were used considered negative. Sufficient samples from cattle, swine, sheep and goats to validate the test were included based on OIE guidelines suggesting inclusion of a minimum of 300 positive and 1000 negative samples.

The improved specificity of bovine brucellosis testing in Great Britain

The brucellosis surveillance scheme in Great Britain includes the serological testing of approximately 1 million bovine samples per year. These are screened by iELISA, positives going forward for confirmatory testing by CFT and SAT. Samples positive by confirmatory testing prompt substantial field investigations and interventions, but the animals involved are usually uninfected. Described below are a series of modifications to the screening method, which have resulted in a 10-fold reduction in false positive results whilst maintaining sensitivity. The key modifications include the introduction of blocking agents, a change in serum test dilution and the introduction of a control that directly defines the positive/negative cut-off. These simple modifications have had a large impact in reducing the cost of the surveillance programme due to reductions in confirmatory test requirements and a knock on effect of reducing costly field intervention.

Second generation competitive enzyme immunoassay for detection of bovine antibody to Brucella abortus

A second generation competitive enzyme immunoassay (CELISA) for detection of bovine antibody to Brucella abortus was developed. This assay was different from previously developed CELISAs in that the detection reagent used was a recombinant combination of the receptor portions of protein A and protein G, labelled with horseradish peroxidase. This eliminates the need for polyclonal anti-mouse-enzyme conjugate reagents for detection thus allowing for true standardization. The assay utilized a monoclonal antibody specific for a common epitope of the O-polysaccharide (OPS) of smooth lipopolysaccharide (SLPS) derived from B. abortus S1119.3 but which did not react with protein A/G. This monoclonal antibody was used to compete with antibody in the bovine test serum. Binding of bovine antibody to the smooth lipopolysaccharide antigen was then measured directly with the protein A/G enzyme conjugate. In this case, development of colour in the reaction was indicative of the presence of bovine antibody. The performance characteristics, sensitivity, specificity and exclusion of B. abortus S19 vaccinated animals, of the assay were very similar to those of the classical CELISA.

Risk factors for brucellosis in indigenous cattle reared in livestock–wildlife interface areas of Zambia

We conducted this cross-sectional study to investigate risk factors of Brucella seropositivity in cattle herds reared in livestock-wildlife interface areas of Blue Lagoon and Lochinvar National Parks in Zambia between August 2003 and September 2004. Sera were collected from cattle aged > or =2 years from 124 herds. Data on husbandry practices, grazing strategies, and herd structure (sex and age composition) were also collected. Sera were screened for anti-Brucella antibodies using the Rose Bengal test (RBT) as a presumptive test and a competitive-ELISA (c-ELISA) as a confirmatory test. A herd was classified as Brucella seropositive if at least one animal tested positive on both RBT and c-ELISA in series testing. Risk factors for herd-level brucellosis seropositivity were tested using multivariable logistic regression; risk factors for increases in the within-herd counts of seropositive cattle were analyzed using the negative binomial regression model with the number of seropositive animals as outcome and total number of cattle tested in a herd as the population at risk (exposure). Of the 110 herds tested, 68 (62; 95% CI: 53, 71% after adjusting for clustering by area) tested seropositive for exposure to Brucella spp. The final logistic-regression model identified geographical area, with Lochinvar (OR=3.4; CI: 0.97, 12) and Kazungula (OR=4.3; CI: 0.91, 20) recording higher odds of Brucella infections compared to Blue Lagoon. Herds coming in contact with wildlife had higher odds compared to those without contact (OR=3.4; CI: 1, 11). Similarly, the odds of Brucella infection were progressively higher in the larger herd categories (26-40 cattle, OR=2.6; CI: 0.70, 10; 41-82 cattle, OR=4.9; CI: 0.93, 26; >82 cattle, OR=9.4; CI: 1.7-51) compared to the smallest herd category (10-25). The negative binomial regression model identified geographical area, contact with wildlife, and herd size as having significant effect on counts of seropositive cattle in a herd.

Evaluation and comparison of fluorescence polarization assay with three of the currently used serological tests in diagnosis of human brucellosis

Fluorescence polarization assay (FPA) is a method that has been used for the diagnosis of brucellosis in animals for many years. To test its possible usefulness for the diagnosis of human brucellosis, 230 sera from patients with clinical signs of brucellosis and positive serological tests (Rose Bengal, Standard Agglutination Test, iELISA), and 305 sera from a healthy population with no clinical/epidemiological/serological evidence were examined with FPA. By using ROC analysis, the cut-off value was estimated at 99 mP, with 93.5% sensitivity (95% CI 89.5-96.3) and 96.1% specificity (95% CI 93.2-97.9). The pairwise comparison of ROC curves between FPA and iELISA and between FPA and RBT revealed no significant statistic difference (P < 0.05). On the contrary it revealed a significant statistic difference between FPA and SAT (P > 0.05). SAT also had the lowest sensitivity (81.7%) among the three tests used in case definition while iELISA had a sensitivity of 90.8% and RBT a sensitivity of 88.7%. The Kappa analysis showed that FPA has a very good agreement (0.92) with the "status of the disease" and with iELISA (0.837). According to our results, FPA seems to be a valuable method for the diagnosis of brucellosis in humans. Taking into consideration the advantages of the method such as the speed of results obtaining, the objectivity of results interpretation, as well as the cost, FPA could be considered as a replacement for other established methods. However, further studies are needed to assess the reproducibility of FPA.

Validation of a fluorescence polarization assay (FPA) performed in microplates and comparison with other tests used for diagnosing B. melitensis infection in sheep and goats

Fluorescence polarization assay (FPA) is a relatively new test for the serological diagnosis of Brucella spp. infection in animals. FPA, carried out in 96-well microplate format, was validated here for diagnosing B. melitensis infection in sheep and goats. This study included sera from 1933 sheep and goats, from animals reared in naturally infected flocks (verified by culture) and showing a positive reaction to two different tests conducted in parallel. In addition, 2154 sera originating from healthy sheep and goats, reared in areas where B. melitensis had never been isolated, were assayed. The optimum cut-off value offering the highest diagnostic sensitivity (DSn) and diagnostic specificity (DSp) was determined at 15 mP over the mean value of the buffer control used in each microplate as determined by receiver operating characteristic analysis. The DSn and DSp of the FPA for small ruminants carried out in microplates at this cut-off value were calculated to be 95.9% and 97.9% with 95% confidence intervals (95% CI) of 94.9-97.7% and 97.2-98.4%, respectively. The accuracy of the FPA, as expressed by determination of the area under the curve, was 0.991. Indirect ELISA and FPA tests offered the highest DSn when compared with the Rose Bengal test, the complement fixation test, the modified Rose Bengal test and competitive ELISA. The parallel or serial combination of FPA with indirect ELISA offers the highest DSn and DSp. As temperature can affect the results of the FPA, all reagents must be at the same temperature and the standard for comparison must always be read under the same conditions as the sera under test. FPA performed in microplates is a promising assay; the DSn and accuracy are better than those of the tests currently approved for diagnosing B. melitensis in small ruminants. Because of its simplicity, speed, and accuracy, this test can improve capacity for laboratory testing and the efficacy of an eradication program based on a test-and-slaughter policy.

Differentiation between serological responses to Brucella suis and Yersinia enterocolitica serotype O:9 after natural or experimental infection in pigs

False-positive serological reactions (FPSR) due to infections with Yersinia enterocolitica serotype Oratio9 (YeOratio9) are a problem in tests for brucellosis. In the present study, FPSR in classical and novel tests for brucellosis following experimental infections of pigs with YeOratio9 were compared with responses of B. suis biovar 2-inoculated pigs. FPSR were limited to 2-9 weeks post-YeOratio9 inoculation, while B. suis-infected pigs were test-positive throughout the 21-week period of investigation. Although YeOratio9-inoculated pigs exhibited FPSR in Brucella tests for a limited period of time, the serological responses in a YeOratio9-purified O-antigen indirect ELISA did not decrease accordingly. Analysis of available cross-sectional serum samples from pig herds naturally infected with YeOratio9 or B. suis biovar 2 confirmed that the observed difference in the duration of the serological responses between the two infections could be used to discriminate between herds infected with B. suis biovar 2 and YeOratio9.

Prevalence of antibodies to Brucella spp. and individual risk Factors of Infection in Traditional Cattle, Goats and Sheep Reared in Livestock–Wildlife Interface Areas of Zambia

A cross-sectional study was performed in the livestock-wildlife interface areas of Lochinvar and Blue Lagoon National Parks and the non-interface area of Kazungula to determine the prevalence of antibodies to Brucella spp. in domestic ruminants and identify individual animal risk factors of infection. A total of 1245 cattle from 124 herds and 280 goats and sheep from 29 flocks were tested sequentially for Brucella antibodies using the Rose Bengal test (RBT) and competitive ELISA. In cattle, individual seroprevalence ranged from 14.1% to 28.1%, while herd sero-prevalence ranged from 46.2% to 74.0% in the three study areas. No goat or sheep tested positive for Brucella antibodies. Three types of cattle grazing strategies were encountered: locally grazed herds (LGH), transhumantly grazed herds (TGH) and river flood plain grazed herds (FGH). Brucella seroprevalence was seen to vary according to area and grazing strategy: Lochinvar and transhumant grazed herds recorded the highest figures, respectively. Age, sex and history of abortion were found to have independent effects on individual seroprevalence. This study establishes that brucellosis is endemic in domestic animals in the livestock-wildlife interface areas of Blue Lagoon and Lochinvar national parks and the disease is also present in Kazungula. We observed that type of grazing strategy had significant impact on cattle Brucella seroprevalence and that transhumant herds were at high risk of being infected.