Serological crossreactivity between Brucella abortus and Yersinia enterocolitica 0:9 III. Specificity of the in vitro antigen-specific gamma interferon test for bovine brucellosis diagnosis in experimentally Yersinia enterocolitica 0:9-infected cattle

The course of immunological reaction in 10 Yersinia enterocolitica 0:9 experimentally-infected heifers was followed using the conventional brucellosis tests complement fixation test (CFT), serum agglutination test (SAT) and brucella card test (BCT), and a recently developed Brucella antigen-specific gamma interferon (IFN-γ) test. Initially, the animals were exposed orally to 10¹⁰ colony-forming units (CFU) of Y. enterocolitica 0:9. Four weeks later, they were inoculated intravenously with 10⁸ CFU of Y. enterocolitica 0:9 cells. After oral inoculation, the response in the conventional brucellosis tests was minimal. Only after intravenous inoculation were CFT and SAT titres and BCT reactions comparable to natural, false positive brucellosis reactors. After oral exposure the Brucellergen-stimulated release of IFN-γ peaked at values above the cut-off stimulation index of 2.5 in 80% of the heifers. After intravenous inoculation, stimulation indices above 2.5 were present in only 10% of the animals. Two B. abortus infected control cattle showed stimulation indices of 3.1 and 3.4, and a negative control animal exhibited a stimulation index of 1.0. These findings show, in contrast to a previous study, that the Brucellergen-specific IFN-γ assay cannot be used as a specific and discriminatory test for B. abortus infections.     

Comparison of three serological tests in the diagnosis of Brucella infection in unvaccinated cattle in Eritrea

Three serological methods, the Rose-Bengal test (RBT), the complement-fixation test (CFT) and an indirect enzyme-linked immunosorbent assay (I-ELISA) were compared for the detection of Brucella-infected animals in unvaccinated cattle herds in Eritrea. In this study, 71 herds first were classified as positive or negative for Brucella infection on the basis of at least one animal being seropositive by RBT and CFT. All the 159 RBT-positive samples from the 26 seropositive herds and 214 RBT-negative samples randomly selected from the seropositive herds and from the 45 negative herds were tested further by CFT and I-ELISA. Using the ELISA titer as main predictor, and incorporating the RBT results, a logistic model was built to predict the CFT-negative or -positive status of individual sera and to estimate sensitivity and specificity. Whilst the ELISA titers (< or =20) accurately predicted all the negative sera in herds that were also negative by the CFT, the number of seropositive animals was higher by ELISA in herds that had positive animals. Serum samples which give higher degrees of agglutination with the RBT need not be re-tested with CFT; consideration of the seropositive status of a herd should be taken into consideration on defining the cut-off optical density readings for ELISA.     

Serological response of cattle after vaccination and challenge with Brucella abortus

New and currently used serological procedures were evaluated using sera from cattle that were challenged with B. abortus S544 (S544) after vaccination with either B. abortus S19 (S19) or B. abortus 45/20 (S45/20) as calves or adults. In animals vaccinated with S19, titres to the indirect haemolysis test (IHLT) rose more slowly, declined more rapidly and involved fewer animals than did titres to the complement fixation test (CFT). In animals vaccinated with S45/20 the rough antigen complement fixation test (RCFT) showed persistent titres. At slaughter the IHLT and CFT were found to be more specific and more sensitive than the Rose Bengal Plate Test (RBPT) and Serum Agglutination Test (SAT) in the detection of cattle infected with B. abortus.     

Field trial of six serological tests for bovine brucellosis

Serum agglutination (SAT), complement fixation (CFT), indirect ELISA (iELISA), competitive ELISA (cELISA), Rose Bengal (RBT) and EDTA-modified agglutination (EDTA) tests were used in parallel on serological samples from 19,935 cattle in 301 herds. The study herds were selected according to putative exposure to Brucellaabortus with cases defined by bacteriological culture or test agreement. No single test identified all infected cattle and, at diagnostic thresholds, relative sensitivity was highest in the iELISA (67.9%) or RBT (78.1%), using bacteriological culture or test agreement, respectively, to define cases. As screening tests, the relative sensitivity of the SAT was highest (75.9% by culture or 84.9% by test agreement), with an optimal threshold of 31 IU. The relative specificity of the diagnostic tests ranged from 99.6% (SAT 31IU) to 100% (iELISA, RBT and CFT). The trial confirmed the value of the SAT as a screening test and the value of parallel testing.     

Monitoring of dairy herds for Brucella abortus infection when prevalence is low

A total of 2,698 dairy herds were surveyed in 1981–1982 in New South Wales and north eastern Victoria in a review of the methods used to monitor them for the presence of Brucella abortus., The methods used to monitor dairy herds were testing of all breeding cows over 1 year of age using the rose bengal test (RBT) and complement fixation test (CFT), the bulk milk ring test (BMRT), and testing of blood samples collected at abattoirs using the RBT and CFT. The surveyed herds had at least one whole herd test, and BMRT was done at regular intervals in the period of the survey. Of the 99 (3.7%) herds that reacted to the BMRT, 91 (3.4%) herds had false positive reactions and 8 (0.3%) herds were declared infected on follow-up herd testing. False-positive reactions were obtained in 22 herds on more than one occasion. Common causes of false positive reactions to the BMRT were thought to be previous vaccination with Strain 19 and sampling in very early or late lactation. Of the 98 (3.63%) herds that reacted to the whole herd serological tests, 80 (2.96%) herds had false-positive reactions and 18 (0.67%) herds were declared infected. Strain 19 vaccination was thought to be an important cause of false-positive reactions. Fifty-three (2.0%) herds showed suspicious reactions on abattoir monitoring but none was declared infected on follow-up testing. Of the 18 herds with infected or equivocal status, the BMRT identified 8. In a further 6 herds, the infected cattle were not in the milking herd. Four other herds had milkers with high CFT titres which could not be confirmed as infected on culture. In no herds were culture positive RBT or CFT reactors from the milking herd detected without the BMRT being positive. The proportion of false-positive reactions to the BMRT was high but the BMRT proved very useful in identifying dairy herds infected with B. abortus, when the prevalence of brucellosis was very low. Aust Vet J, 64 : 97–100     

An evaluation of the anamnestic test for brucellosis in cattle of the northern pastoral area

SUMMARY An investigation of the anamnestic test for brucellosis using Brucella abortus 45/20 vaccine was carried out in 3 groups of weaner cattle on 2 farms in western Queensland. Each group originally consisted of about 500 cattle. They were bled before and at 6 or 10 weeks after vaccination and again in the following year. The serums were tested by the complement fixation (CFT), Rose Bengal (RBT) and indirect haemolysis tests (IHLT). Most of the cattle reacting to one or more of the tests were killed and selected tissues were subjected to bacteriological examination for B. abortus. B. abortus was isolated from 19 of 30 (63%) pre-vaccinal reactors, 23 (24%) of 96 cattle reacting at 6 or 10 weeks after vaccination (the anamnestic test) and 1 (2%) of 50 cattle reacting one year after vaccination. The reactor found to be infected the year after vaccination had high serological titres in each of the 3 serological tests: RBT of 3, CFT of 128 and IHLT of 256. A subsequent test showed the group to be brucellosis-free. The CFT was the most efficient test. In the pre-vaccination tests 17 of 19 infected animals were positive in the CFT compared with 11 positive in the IHLT and 17 in the RBT. In post vaccination tests 22 of 23 infected animals were positive in the CFT compared with 18 in the IHLT and 19 in the RBT. At the pre-vaccinal and anamnestic tests (6 or 10 weeks after vaccination) 19 of 57 (33%) cattle with CF titre of 4 or 8 yielded B. abortus on culture compared with none of 26 cattle with similar titres in the year after vaccination. The interpretation of CF titres in cattle following 45/20 vaccination needs to be re-examined.     

Use of serology and real time PCR to control an outbreak of bovine brucellosis at a dairy cattle farm in the Nile Delta region,Egypt

Background

Bovine brucellosis remains one of the most prevalent zoonotic infections affecting dairy cattle in developing countries where the applied control programs often fail. We analyzed the epidemiologic pattern of bovine brucellosis in a dairy cattle herd that showed several cases of abortions after regular vaccination with RB51 (B. abortus vaccine). In 2013 thirty dairy cows, from a Holstein-Friesian dairy herd with a population of 600 cattle, aborted five months post vaccination by a regular RB51 vaccine. Blood samples were drawn from milking cows and growing heifers, as well as heifers and cows pregnant up to 6 months. These samples were collected in June 2013 (n?=?257) and May 2014 (n?=?263) and were tested by real time (rt)-PCR as well as serological tests, in particular Rose Bengal Test (RBT), Enzyme-Linked Immunosorbent Assays (ELISA) and Fluorescence Polarization Assay. Tissue specimens were also collected from an aborted fetus and cultured. Isolates were subjected to bacteriological typing tests at the genus and species levels.

Results

Five months post vaccination with RB51 vaccine, Brucella (B.) DNA was detected in blood samples of cows by rt-PCR. The serological tests also revealed the spread of Brucella field strains within the herd in 2013. Four Brucella isolates were recovered from specimens collected from the aborted fetus. These isolates were typed as follows: one B. abortus RB51 vaccine strain and three isolates of B. abortus field strain. The seropositive cows with positive rt-PCR might indicate an infection by the Brucella field strain; while the positive rt-PCR results from seronegative animals may either be due to circulating RB51 vaccine DNA in vaccinated animals or to circulating field strain in infected animals before seroconversion.

Conclusion

The results herein suggest that PCR can be a good supplementary tool in an outbreak situation, if an assay is available that can differentiate vaccine and field strains with a high analytical sensitivity. We recommend using RBT and ELISA in parallel in outbreak situations, to identify as many infected animals as possible during the initial screenings. This test procedure should be repeated for at least three successive negative tests, with one month interval.

     

Application of an enzyme-linked immunosorbent assay in the final stages of a bovine brucellosis eradication program

Bovine field serums from the Australian brucellosis eradication program were used to compare 2 enzyme linked immunosorbent assays (ELISA) with the complement fixation test (CFT) and Rose Bengal test (RBT). One ELISA used an anti-bovine IgG horseradish peroxidase conjugate (ELISA 1) and the other a monoclonal anti-bovine Ig alkaline phosphatase conjugate (ELISA 2). When compared with the CFT, the ELISA 2 like the ELISA 1 lacked specificity in B. abortus vaccinated herds but the ELISA 2 was more specific than the ELISA 1 in previously infected herds and equally as specific as the ELISA 1 in nonvaccinated Brucella free herds. In this study the ELISA 2 proved more sensitive than the CFT, RBT and ELISA 1 particularly in herds where B. abortus biotype 2 was present. The value of using the ELISA 2 in conjunction with the CFT in an eradication program is discussed.     

Applied serology in the latter stages of the eradication of bovine brucellosis

Late in the program to eradicate bovine brucellosis from Western Australia, Rose Bengal test (RBT) and complement fixation test (CFT) results on the serums from 2,307 cattle (from herds where infection was still present after a minimum of 3 complete herd tests) showed that 327 were positive in the CFT and 246 were positive in the RBT (p less than 0.001). Subsequent testing by the RBT, CFT and the indirect haemolysis test (IHLT) of 722 serums from cattle slaughtered as part of infected herds showed that of 177 cattle positive on culture, 138 were positive in all 3 tests, 9 were negative in all 3 tests and no animal positive on culture had a reaction only in the RBT. In the 177 cattle from which B. abortus was isolated, positive reactions in the CFT occurred in the serums of 159 of them. Application of the RBT as a screening test followed by a confirmatory CFT would have resulted in 149 of the 177 cattle being positive and application of the CFT/IHLT (double test) on the serums of all cattle in the herds would have resulted in 168 or the 177 being regarded as positive.     

Evaluation of different enzyme-linked immunosorbent assays for the diagnosis of brucellosis due to Brucella melitensis in sheep

Six serological assays for the diagnosis of ovine brucellosis, due to Brucella melitensis were evaluated. Reference serum samples from sheep of known B. melitensis infection status (n = 118) were assessed using the Rose Bengal test (RBT), complement fixation test (CFT) and four commercial enzyme-linked immunosorbent assays (ELISAs), including two indirect ELISAs (iELISAs), one competitive ELISA (cELISA) and one blocking ELISA (bELISA).The highest differential positive rates (DPR) were obtained with the cELISA and bELISA, while the lowest DPR was estimated using iELISAs. A latent class analysis was performed to estimate the accuracy of the CFT, RBT and bELISA using 1827 sera from sheep undergoing testing as part of a surveillance and control programme. Lower sensitivity and specificity were obtained for the three serological tests when the field samples were used. A higher DPR was achieved by the CFT, compared to bELISA and RBT. The results suggest that ELISAs, and particularly the bELISA, might be suitable for inclusion in the European Union legislation on intra-community trade for diagnosing B. melitensis infection in sheep, as it has a similar test performance compared to the RBT.     

Validation of an indirect enzyme-linked immunosorbent assay for the detection of antibody against Brucella abortus in cattle sera using an automated ELISA workstation

An automated indirect enzyme-linked immunosorbent assay (I-ELISA) for the serological diagnosis of bovine brucellosis was developed and validated in-house. A total of 4,803 cattle sera from South Africa (n = 3,643), Canada (n = 652), Germany (n = 240), France (n = 73) and the USA (n = 195) was used. The South African panel of sera represented 834 sera known to be positive by the Rose Bengal test (RBT), serum agglutination test (SAT) and complement fixation test (CFT), 2709 sera that were negative by CFT, and 100 sera from animals vaccinated with a standard dose of Brucella abortus strain 19. Overseas sera were obtained from reference non-vaccinated brucella-free cattle (n = 834), naturally infected (n = 72), experimentally infected (n = 71), and vaccinated animals (n = 83). Also 100 sera collected from cattle in Canada and known to be positive by competitive ELISA (C-ELISA) were used. The intermediate ranges ("borderline" range for the interpretation of test results) were derived from two-graph receiver operating characteristics analysis. The lowest values of the misclassification cost-term analysis obtained from testing overseas panels, covered lower I-ELISA cut-off PP values (0.02-3.0) than those from local panels (1.5-5.0). The relatively low cut-off PP values selected for I-ELISA were due to the fact that the positive control used represents a very strong standard compared to other reference positive sera. The greater overlap found between negative and positive cattle sera from South Africa than that between reference overseas panels was probably due to the different criteria used in classifying these panels as negative (sera from true non-diseased/non-infected animals) or positive (sera from true diseased/infected animals). The diagnostic sensitivity of the I-ELISA (at the optimum cut-off value) was 100% and of the CFT 83.3%. The diagnostic specificity of I-ELISA was 99.8% and of the CFT 100%. Estimate of Youden's index was higher for the I-ELISA (0.998) than that for the CFT (0.833). Analysis of distribution of PP values in sera from vaccinated and naturally infected cattle shows that in vaccinated animals all readings were below 31 PP where in infected ones these values represented 43%. Therefore, it appears that I-ELISA could be of use in identifying some naturally infected animals (with values > 31 PP), but more sera from reference vaccinated and infected animals need to be tested to further substantiate this statistically. Of 834 sera positive by RBT, SAT and CFT, 825 (98.9%) were positive in the I-ELISA. Compared to C-ELISA the relative diagnostic sensitivity of the I-ELISA was 94% and of the CFT 88% when testing 100 Canadian cattle sera. Of 258 South African cattle sera, of which 183 (70.9 %) were positive by the I-ELISA and 148 (57.4 %) by the CFT, 197 (76.4%) were positive by C-ELISA when re-tested in Canada. One has to stress, however, that Canadian C-ELISA has not been optimised locally. Thus, the C-ELISA was probably not used at the best diagnostic threshold for testing South African cattle sera. This study shows that the I-ELISA performed on an automated ELISA workstation provides a rapid, simple, highly sensitive and specific diagnostic system for large-scale detection of antibodies against B. abortus. Based on the diagnostic accuracy of this assay reported here, the authors suggest that it could replace not only the currently used confirmatory CFT test, but also the two in-use screening tests, namely the RBT and SAT.     

Investigation of bovine brucellosis in the Northeastern Turkey

Bovine brucellosis, caused by Brucella abortus, is a significant problem for both public and animal health in Turkey. This study was conducted on the calving seasons between 2001 and 2006. A total of 626 serum samples of cattle obtained from 27 herds with a history of abortions was examined for Brucella antibodies by RBPT, SAT and ELISA. Of the cattle sera analysed, 221 (35,30%) and 206 (32, 92%) and 247 (39,45%) were found to be positive by RBPT , SAT and ELISA, respectively. B. abortus was isolated from 48 (32,21%) of 149 lung samples and stomach contents of the aborted fetuses. Based on the biochemical tests and the agglutination tests with monospecific A and M antisera, only 3 of the isolates were found to be B. abortus biotype 1 and the remaining 45 were biotype 3. This study also revealed that the dominant biotype of B. abortus was biotype 3 in this region. The determination of the agents responsible for bovine brucellosis and serosurvey of this disease are expected to help better understanding of this zoonotic infection in this region and neighbouring countries.     

Vaccination of cattle with chemically modified and unmodified salt-extractable proteins from Brucella abortus

Beef heifers were vaccinated on Day 0 with either salt-extractable protein (CSP) or chemically modified CSP (dCSP) from Brucella abortus Strain 19 in Freund's complete adjuvant (FCA). Six weeks later, vaccination was repeated, and heifers received either the homologous or heterologous vaccine. Another group of heifers received only FCA and saline. Vaccinations with CSP or dCSP stimulated marked antibody responses to B. abortus, as detected by standard serologic tests, an enzyme-linked immunosorbent assay, or a quantitative fluorametric immunoassay. Twelve percent of the heifers were seropositive by the CARD test 1 year after vaccination. Vaccination stimulated an increased cell-mediated immune response as measured by lymphocyte blast transformation (LBT) to B. abortus antigens. Fifty-six weeks after the initial vaccination, the heifers were challenged intraconjunctivally with 1.9 × 10⁷ colony-forming units of B. abortus strain 2308. Sixty to 83% of the heifers aborted in each group and 70–83% of the heifers were culture positive. There were no significant differences (P>0.05) among groups with respect to the number of abortions or the number of culture-positive heifers. Antibody responses increased rapidly within 4 weeks after challenge. Overall, antibody responses were greater for heifers that aborted than for those that did not abort. These differences were significant (P<0.05) only as measured by the fluorometric procedure. The LBT responses appeared to be higher for vaccinates than for the control group, but these differences were not significant (P>0.20). There was a significantly lower (P<0.05) LBT response to heat-killed B. abortus in those heifers that aborted compared to those that did not.     

The first report in new zealand of Lymnaea columella say (Mollusca: gastropoda) an intermediate host of the liver fluke Fasciola hepatica L

Six herds of dairy cattle, in which infection had persisted after measures had been employed to eradicate brucellosis, were investigated in detail. One hundred and two animals out of 700 (14.6%) had evidence of the disease from cultural or serological tests. Only 4 infected animals aborted; the remaining 98 animals with brucellosis exhibited no clinical sign of the disease, and 52 were heifers calving for the first time. Sixty-five of the 700 animals (9.3%) produced brucella-infected vaginal discharges at the end of a normal period of gestation, and another 17 (2.4%) were detected only by the brucellosis (Brewer) card test (BCT) or complement fixation test (CFT). All the infected animals were removed from the herds immediately after detection.

About 2 weeks after all the cows had calved, 20 of the remain-ing 510 animals (3.9%) in 4 of the herds became positive to one or more tests and 8 excreted brucellae in their milk. The pregnancy of three 2-year-old primiparous heifers terminated normally and one aborted. All four discharged brucellae until they were slaughtered 20 to 35 days after parturition.

Twenty-five of the 102 infected animals were detected by bacteriological, and 29 by serological, means only. A compari-son was made of the results of the testsfrom 73 culturally positive animals; 4.1% of the sera were CFT positive but BCT negative, and 5.5% were BCT positive but CFT negative. An attempt has been made to explain the large numbers (34.2%) of infected animals that were serologically negative.     

THE INDIRECT HAEMOLYSIS TEST (IHLT) FOR BOVINE BRUCELLOSIS—COMPARISONS WITH THE COMPLEMENT FIXATION TEST (CFT) IN VACCINATED AND EXPERIMENTALLY INFECTED CATTLE

SUMMARY Cattle were vaccinated with Brucella abortus strain 19 subcutaneously in doses ranging from the normal (2.0 ml) dose of standard vaccine down to 1/400 of the normal dose, and via the conjunctival sac with 1/2 or 1/20 of the normal dose. Under all vaccination regimes serum antibody titres in the complement fixation test (CFT) rose more rapidly, reached higher levels, declined more slowly and involved a greater proportion of animals, than titres in the indirect haemolysis test (IHLT). The interval between the first positive serological test and parturition was determined for 54 pregnant cows infected with a virulent field strain (VRI 3) of B. abortus. On average the CFT titre rose to 1/4 43 days, and 1/8 33 days, before parturition, while the IHLT reached a 2/8 reaction 31 days before parturition.     

Assessment of milk ring test and some serological tests in the detection of <Emphasis Type="Italic">Brucella melitensis</Emphasis> in Syrian female sheep

Brucella melitensis infection prevalence among Syrian female sheep, to evaluate a number of serological tests and to discuss some epidemiological aspects of brucellosis, was studied. A total of 2,580 unvaccinated Syrian female sheep sera samples were tested for B. melitensis antibodies detection using four serological methods: the Rose Bengal test (RBT), the serum agglutination test (SAT), the complement fixation test (CFT) and an indirect enzyme-linked immunosorbent assay (iELISA). In addition, 2,375 milk samples were collected, then milk ring test (MRT) and bacterial isolation test were employed to evaluate the natural organism shedding. The samples were considered positive in 66%, 64%, and 60% when we employed the RBT, SAT, and iELISA tests, respectively. Whereas, the CFT test revealed the smallest number of positive samples. By using the MRT, the total prevalence of brucellosis was nearly 38% of samples. A large variation was observed concerning the studied areas, ranging from 24% in Tartous to 44% in both Damascus and Damascus rural areas. Brucella was isolated from only 677 samples out of the 2,375 female sheep milk samples.     

Rapid immunofiltration assay based on colloidal gold–protein G conjugate as an alternative screening test for bovine and ovine brucellosis

A non-enzymatic rapid immunofiltration assay (NERIFA) was developed as an alternative field test for rapid detection of anti-Brucella antibody in bovine and ovine sera. The assay was based on Brucella abortus lipopolysaccharide as diagnostic antigen and colloidal gold particle–protein G conjugate as detection reagent. Its diagnostic performance was evaluated using undiluted well-defined positive and negative serum samples in comparison with Rose Bengal test (RBT), complement fixation test (CFT) and a commercial and an in-house indirect enzyme-linked immunosorbent assay (ELISA). A perfect test agreement was found between NERIFA and ELISAs by kappa statistics. In addition, McNemar’s analysis of the results showed that the RBT for bovine sera and the CFT for ovine sera were found significantly less performant than indirect ELISAs and NERIFA. The results of the present study indicated that the NERIFA could be considered as a simple, rapid, and accurate field test for screening of ovine and bovine brucellosis. Therefore, this test constitutes a high potential to be used as an alternative model particularly in brucellosis prevalent tropical and subtropical geographical areas.     

The Dutch Brucella abortus monitoring programme for cattle: the impact of false-positive serological reactions and comparison of serological tests

The Dutch national Brucella abortus eradication programme for cattle started in 1959. Sporadic cases occurred yearly until 1995; the last infected herd was culled in 1996. In August 1999 the Netherlands was declared officially free of bovine brucellosis by the European Union. Before 1999, the programme to monitor the official Brucella-free status of bovine herds was primarily based on periodical testing of dairy herds with the milk ring test (MRT) and serological testing of all animals older than 1 year of age from non-dairy herds, using the micro-agglutination test (MAT) as screening test. In addition, serum samples of cattle that aborted were tested with the MAT. The high number of false positive reactions in both tests and the serum agglutination test (SAT) and complement fixation test (CFT) used for confirmation seemed to result in unnecessary blockade of herds, subsequent testing and slaughter of animals. For this reason, a validation study was performed in which three indirect enzyme-linked immunosorbent assays (ELISAs), the CFT and the SAT were compared using a panel of sera from brucellosis-free cattle, sera from experimentally infected cattle, and sera from cattle experimentally infected with bacteria which are known to induce cross-reactive antibodies (Pasteurella, Salmonella, Yersinia, and Escherichia). Moreover, four ELISAs and the MRT were compared using a panel of 1000 bulk milk samples from Brucella-free herds and 12 milk samples from Brucella abortus- infected cattle. It is concluded that the ELISA obtained from ID-Lelystad is the most suitable test to monitor the brucelosis free status of herds because it gives rise to fewer false-positive reactions than the SAT.     

Serological and bacteriological responses of water buffalo (Bubalus bubalis) vaccinated with two doses of Brucella abortus strain RB51 vaccine

Thirty-two water buffalo (Bubalus bubalis) calves aged 6?C10?months were used to evaluate serological responses to Brucella abortus strain RB51 (RB51) vaccination in a dose?Cresponse study and to compare the use of two selective media for the isolation of RB51. The animals were randomly divided into three treatment groups. Groups I?CIII received the recommended vaccine dose (RD) twice 4?weeks apart, RD twice 18?weeks apart and saline once, respectively. Lymph nodes were excised from the three groups and subjected to bacteriological examination to determine the frequency of detection of RB51. Pre- and post-vaccination blood samples were collected and tested for B. abortus antibodies using the buffered plate agglutination test (BPAT), complement fixation test (CFT), and dot-blot assay. Sera taken at all post-inoculation weeks (PIW) were negative for field strain B. abortus using the BPAT. Antibody responses to RB51 were demonstrated in all vaccinates but not in controls by CFT and dot-blot assay from 1 PIW up to 16?weeks following booster vaccination. The agreement for both assays was 80.7% and there was a linear interdependence with a Pearson??s correlation coefficient value of 0.578. The frequency of isolation of RB51 from the two selective media used was not significantly different (P?>?0.05).     

Investigations on the Prevalence of Bovine Tuberculosis and Brucellosis in Dairy Cattle in Dar es Salaam Region and in Zebu Cattle in Lugoba Area,Tanzania

A study between August 1995 and December 1997 included 343 dairy cattle on 20 farms in the Dar es Salaam region and 2289 zebu cattle on 39 bomas in the Lugoba area (coast region). The aim was to establish the prevalence of bovine tuberculosis (Mycobacterium bovis) and bovine brucellosis (Brucella abortus). In the single intradermal tuberculin test (SIT), 0.9% (3/343) of the animals in Dar es Salaam tested positive and 1.2% (4/343) were doubtful. Positive reactors were found in 10% (2/20) of the farms. In the Lugoba area, 0.6% (14/2206) were positive and 6.8% (149/2206) doubtful, positive cases being found in 21% (8/39) of all bomas. In the slow agglutination test (SAT) for B. abortus, 14.1% (48/341) of the serum samples reacted positively in Dar es Salaam and 2.3% (8/341) were doubtful. Positive SAT reactors were identified on 25% (5/20) of the dairy cattle farms. In the Lugoba area, 12.3% (273/2221) proved to be positive SAT reactors and doubtful reactions were observed in 2.9% (64/2221). SAT-positive animals were detected on 87% (34/39) of all bomas. The prevalence in single herds in Dar es Salaam varied from 4.3% to 5.3% for the SIT and from 2.2% to 50% for the SAT. The prevalence in single herds in Lugoba area was between 1.1% and 2.9% for SIT and from 1.4% up to 62.1% for SAT. The two cattle populations differed significantly (p<0.001) in the prevalence of both bovine tuberculosis and bovine brucellosis. Two cows that were positive reactors were slaughtered and subjected to post-mortem examination, and organ samples were bacteriologically cultured. The occurrence of Mycobacterium tuberculosis was confirmed by polymerase chain reaction (PCR) in both cows.