Use of the complement fixation and brucellin skin tests to identify cattle vaccinated with Brucella abortus strain RB51

In the European Union, RB51 vaccine can be used only under strictly controlled conditions for the immunisation of cattle at risk of infection with Brucella abortus. A test is therefore necessary to distinguish vaccinated from unvaccinated animals. The complement fixation test with RB51 antigen (RB51-CFT), dot-blot and gamma-interferon used to identify vaccinated animals have been described, but sensitivity of the tests has been poor and positivity transient after calfhood vaccination. To avail of a rapid and accurate diagnostic tool, the authors produced, controlled and evaluated an experimental brucellin prepared from strain RB51 (RB51 brucellin). The potency of this brucellin was evaluated in guinea-pigs sensitised with RB51 and compared with a commercially available brucellin. Both allergens produced similar biological activity in guinea-pigs. The RB51 brucellin skin test was performed in 10 cattle 414 days after calfhood vaccination with RB51 when they were negative to the RB51-CFT. The skin test revealed 60% sensitivity (with a confidence interval of 95%, CI 30.8%-83.3%) and 100% specificity (CI 60.7%-100%). These findings limit the use of the skin test only for screening to detect RB51 vaccinated herds, not individual animals. Nevertheless, following intradermal inoculation of RB51 brucellin, a transient antibody increase to the RB51-CFT was observed, from day 9 to day 20 post inoculation with RB51 brucellin. This transient antibody increase, when evaluated in parallel with the RB51 brucellin skin test results, enables detection of individual vaccinated animals (sensitivity 100%; CI 76.2%-100%).

Evaluation of an indirect ELISA for the detection of Brucella antibodies in cow's milk

An indirect ELISA was developed by the Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise 'G. Caporale' (IZS A&M) for the detection of Brucella antibodies in cow's milk. Specific monoclonal antibody was used against a bovine IgG(1) epitope and complies with European Commission requirements. The test accuracy was evaluated on milk samples from the regions of Abruzzo and Molise in Italy. The negative samples came from 1,250 officially brucellosis-free herds from the Molise region (Italy). The positive samples were taken from three herds in the Abruzzo and Molise regions where animals positive to the official tests were present and Brucella abortus was isolated. Test specificity was 99.8% (with a confidence interval [CI] of 99.6%-99.9%), while sensitivity was 100% (CI 91.2%-100%). The probability of detecting antibodies in positive milk samples was higher than 50% up to a dilution of 1:256 in negative milk. The probability of identifying an infected herd in the dairy cattle population. Under study was 88.6% (CI 73.9%-95.3%).

The Use of Homologous Antigen in the Serological Diagnosis of Brucellosis Caused by Brucella melitensis

In the European Union the serological diagnosis of brucellosis caused by Brucella melitensis is performed using the heterologous antigen of B. abortus S99. The possible higher sensitivity or ability of an early detection of antibodies by a homologous antigen may prove very useful in the final phases of an eradication programme. Results obtained in sheep experimentally infected by B. melitensis biovar 3 were compared using B. abortus S99, B. melitensis M1, M2 and M3 antigens in the Rose Bengal plate test (RBPT), the complement fixation test (CFT) and an enzyme-linked immunosorbent assay (ELISA) test. Forty-six sheep from an officially brucellosis-free flock were experimentally infected intraconjunctivally with B. melitensis biovar 3. Prior to infection, all animals were tested first against Brucella antibodies, weekly for 2 months post-infection (PI) and then monthly for a further 7 months. All sera were tested against the antigens listed above using RBPT, CFT and ELISA. Using a Bayesian approach, test sensitivities were estimated and compared. Their ability for the early detection of antibodies was evaluated through a regression model based on a logit response model, using the number of days PI as the independent variable and the logit of the fraction of positive animals as the dependent variable. No significant differences were detected among the various antigens used, either in terms of sensitivity or in terms of antibody kinetics; however, the CFT was significantly less sensitive than the RBPT and ELISA and it also showed a lower rate of increase of percentage positive animals (beta-coefficient of regression analysis).

Bluetongue laboratory diagnosis: a ring test to evaluate serological results using a competitive ELISA kit

The occurrence of bluetongue (BT) in Italy prompted an increase in disease surveillance. Thus a competitive enzyme-linked immunosorbent assay (c-ELISA) to detect immunoglobulins to BT virus (BTV) was developed and distributed amongst 27 laboratories comprising the Italian veterinary diagnostic laboratories network to screen field sera. This ring test enabled comparison of the results and the evaluation of the reproducibility of the method. The c-ELISA developed by the National Reference Centre for Exotic Diseases (c-ELISA-IZSA&M) was compared also against a commercially available c-ELISA. In addition, results obtained by the Centre of Athens Veterinary Institutions are presented.

Serological response in cattle and sheep following infection or vaccination with bluetongue virus

Data from various experimental and field studies were compiled and analysed to evaluate the serological response in sheep and cattle against different bluetongue (BT) virus (BTV) vaccine combinations (Onderstepoort Biological Products, South Africa); the accuracy of diagnostic procedures commonly used for detecting BTV antibodies was also assessed. Using the competitive enzyme-linked immunosorbent assay (c-ELISA) (IZSA&M, Teramo, Italy) and the virus neutralisation (VN) test, antibody responses were evaluated under the following vaccination regimes: monovalent modified-live vaccine against BTV-2 in cattle and sheep, monovalent modified-live vaccine against BTV-9 in sheep, and bivalent modified-live vaccine against BTV-2 and BTV-9 in cattle and sheep. The data were compared to serological results observed in cattle and sheep infected with Italian field strains of BTV-2 or BTV-9. The c-ELISA consistently detected antibodies earlier than the VN test in both livestock species and against all BTV serotypes. The highest and most rapid antibody responses were observed in sheep infected in the field. In cattle and in sheep, high VN titres were detected using monovalent vaccines, while bivalent vaccines initiated lower antibody titres that developed more slowly.

Serological surveillance of bluetongue virus in cattle, sheep and goats in Albania

The recent spread of the bluetongue (BT) virus (BTV) in the Mediterranean Basin encouraged numerous countries to undertake entomological and serological surveillance programmes to identify affected areas and control the infection. Hitherto, no data on the presence and diffusion of BTV in Albania were available. Between October and November 2002 serum samples from 857 cattle and 870 sheep and goats were collected by the Albanian Veterinary Services in 15 districts, some bordering Yugoslavia, Macedonia and Greece, and others along the Adriatic coast. At the Albanian Veterinary Research Institute the samples were tested for the presence of BTV antibodies using a competitive enzyme-linked immunosorbent assay (c-ELISA) (bluetongue antibody test kit, IZS A&M, Teramo); in Italy, the virus neutralisation (VN) test was used to confirm the ELISA results and determine the serotype of BTV circulating. Overall seroprevalence was 18.9% in cattle and 4.4% in sheep and goats; seropositive animals occurred in all districts surveyed. The highest prevalence of BT was observed in the Tirana District, with 61% of the cattle and 20% of the sheep and goat populations BT-positive. The VN test confirmed the c-ELISA results revealing the presence of antibodies against BTV serotype 9.

Model proficiency testing scheme for serological diagnosis of Brucellosis: interlaboratory study

A model interlaboratory testing scheme was developed by the Italian National Reference Laboratory for Brucellosis. This scheme was planned for both qualitative (Rose Bengal Plate Test; RBPT) and quantitative (Complement Fixation Test; CFT) serological tests and involved a total of 42 laboratories. In the preparation of this scheme, reference was made to general protocols and guidelines and to methods reported in the literature, which were applicable to analytical chemistry laboratories. Six field sera from naturally infected animals, one positive serum at a titer below the European Union (EU) positivity threshold, and 5 sera positive at titers between 20 and 851 International Units of Complement Fixation Test (IUCFT)/mL plus one negative serum were used to produce a panel of test sera. To evaluate laboratory performances in the quantitative test for each tested sample examined, z-scores based on robust summary statistics (the median and normalized interquartile range) were used. To evaluate overall laboratory performance, 2 types of combined z-scores were used: Rescaled Sum of Scores and Sum of Squared Scores. In the case of the qualitative test (RBPT), results were analyzed by a Bayesian approach. A Beta distribution, based on the result of each laboratory, was calculated and used to estimate the probability of each laboratory giving a correct result and its uncertainty.

Kinetics of the antibody response in ewes experimentally infected with Brucella melitensis biovar 3

The authors evaluated the kinetics of antibody response in 46 ewes coming from officially brucellosis free flocks that were experimentally infected with Brucella melitensis biovar 3, and monitored through three subsequent reproductive cycles. In this study, results of Rose Bengal test (RBT) and complement fixation test (CFT) were considered. Test results of 2nd and 3rd reproductive cycle show a peak in the antibody production at parturition, followed by a drop in the following months. The peak at parturition is significantly lower in the 3rd reproductive cycle compared to the 2nd. The drop in antibody production observed after parturition of the 3rd reproductive cycle is significantly higher than that observed after parturition of the 2nd reproductive cycle. Nevertheless, the infection can still be revealed at flock level after three years post infection.

Sensitivity and specificity of serological and bacteriological tests for contagious bovine pleuropneumonia

In 1990 an outbreak of contagious bovine pleuropneumonia (CBPP) occurred in Italy. Subsequent surveillance for CBPP was based on random sampling in bovine herds, serological controls on all animals moved from the herd of origin and controls on slaughtered animals. Official tests employed were the complement fixation test (CFT) and bacteriological isolation and typing. A total of 33,856 serum samples collected from herds in CBPP-free regions were used to define CFT specificity, while samples from 595 animals from infected herds were employed to define the sensitivity. Ninety-nine animals from three infected herds were used to estimate the sensitivity of the isolation technique. Results showed the specificity of CFT (threshold +1:10) to be 98% and sensitivity to be 63.79%. The sensitivity of the test did not change significantly, regardless of whether the lesions were caused by acute or chronic infection. The sensitivity of the isolation technique was 54.1%.