Seroepidemiology of bovine brucellosis in Colombia's preeminent dairy region, and its potential public health impact

A cross-sectional study was conducted to determine the associated factors of brucellosis in Colombia's preeminent dairy region declared in quarantine. A total of 656 samples were collected from cows ≥ 2-year-old from 40 herds. Samples were screened by the Rose Bengal Plate Test, and the Fluorescence Polarized Assay test and Competitive ELISA were used as confirmatory tests. A cow was classified as positive if the screening and both confirmatory tests were positive. A herd was classified as positive if at least one cow was seropositive. The factors associated to seropositivity were tested using a logistic regression model with explanatory variables regarding cattle management, zootechnical parameters, and sanitary practices. The seroprevalence at the animal level was 6.6% (43/656) and at herd level 27.5% (11/40). In the model, five variables explained the animal cases: purchase or animal transfer between owner's farms (OR = 2.79, 95% CI 1.42, 5.49), history of abortion (OR = 4.22, 95% CI 1.91, 9.33), birth of weak calves (OR = 13.77, 95% CI 2.75, 68.91), use of a bull for mating (OR = 9.69, 95% CI 2.23, 42.18), and the vaccination in adulthood (OR = 3.03, 95% CI 1.04.8.78). In the model at the herd level, two variables explained the cases: birth of weak calves (OR = 9.60, 95% CI 1.54, 59.76) and purchase or animal transfer between owner's farms (OR = 7.22, 95% CI 1.03, 50.62). These results justify the need for a quarantine declaration in the region and the implementation of epidemiological studies as a public health measures used to combat outbreak.

Polymorphism of cytokine and innate immunity genes associated with bovine brucellosis in cattle

Genetic susceptibility to brucellosis is multifactorial, and it is known that impairment of the immune system could contribute to risk for getting brucellosis. The aim of the study was to find association of bovine brucellosis with 20 SNPs pertaining to bovine cytokine (IFNG, IFNGR1, IFNGR2, TNFA) and innate immunity (SLC11A1, TLR1, TLR4, and TLR9) genes using PCR-RFLP genotyping technique and it was observed that SLC11A1 (+1066 C/G), TLR1 (+1446 C/A), TLR1 (+1380 G/A), TLR4 (+10 C/T) and TLR4 (+399 C/T) loci were significantly (P≤0.05) associated with bovine brucellosis. The odds ratios (OR) of CG and CC genotypes versus GG genotype were 0.31 (0.12-0.82; 95% CI) and 0.18 (0.03-1.06; 95% CI) at SLC11A1 (+1066 C/G) locus in cases of brucellosis affected cattle. For TLR1 (+1380 G/A) locus, the OR for AG and AA genotypes versus GG genotypes were 0.15 (0.05-0.44; 95% CI) and 0.26 (0.04-1.47; 95% CI) which indicated that proportion of GG homozygote was significantly higher in brucellosis affected animals as compared to control. At TLR1 (+1446 C/A) locus the OR of AC genotype versus CC genotype was 0.24 (0.08-0.68; 95% CI) which revealed that relative proportion CC genotypes was significantly higher in case population. The TLR4 (+10 C/T) locus had three genotypes (TT, CT and CC) where OR of CT and CC genotypes versus TT genotype were near to zero. The OR of CT genotypes versus CC genotypes was 8.25 (0.94-71.92; 95% CI) at TLR4 (+399 C/T) locus and indicated that CT genotype had higher odds of bovine brucellosis than control animals.

Safety and immunogenicity of Brucella abortus strain RB51 vaccine in cross bred cattle calves in India

Safety and immunogenicity of Brucella abortus RB51 vaccine has been evaluated in an organised dairy farm in India. All the cattle (r = 29) vaccinated with strain RB51 'responded' to the vaccine as demonstrated by iELISA using acetone killed strain RB51 antigen. The percentage responders at day 35, 60 and 90 post vaccination were 100%, 95% and 20%, respectively. Strain RB51 was able to elicit a good IFN-gamma response from vaccinated animals. The post-vaccination time point analysis indicated that the cumulative IFN-gamma response of whole blood from vaccinates stimulated with heat killed RB51 antigen was elicited in 80% of calves at 60 days post vaccination. Absence of strain RB51 in the secretions and excretion and lack of local or systemic reaction indicated the safety of the vaccine.

Diagnostic and vaccine chapter

The first report in this chapter describes the development of a killed composite vaccine. This killed vaccine is non-infectious to humans, other animals, and the environment. The vaccine has low reactivity, is non-abortive, and does not induce pathomorphological alterations to the organs of vaccinated animals. The second report of this chapter describes the diagnostic value of a competitive enzyme-linked immunosorbent assay for detecting Brucella-specific antibodies and its ability to discriminate vaccinated cattle from infected cattle. The results indicated that the competitive enzyme-linked immunosorbent assay is more sensitive than traditional tests for detecting antibodies to Brucella abortus in naturally and experimentally infected cattle.

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.

NRAMP1 3' untranslated region polymorphisms are not associated with natural resistance to Brucella abortus in cattle

The NRAMP1 gene encodes a divalent cation transporter, located in the phagolysosomal membrane of macrophages, that has been associated with resistance to intracellular pathogens. In cattle, natural resistance against brucellosis has been associated with polymorphisms at the 3' untranslated region (3'UTR) of the NRAMP1 gene, which are detectable by single-strand conformational analysis (SSCA). This study aimed to evaluate the association between NRAMP1 3'UTR polymorphisms and resistance against bovine brucellosis in experimental and natural infections. In experimentally infected pregnant cows, abortion occurred in 42.1% of cows with a resistant genotype (SSCA(r); n = 19) and in 43.1% of those with a susceptible genotype (SSCA(s); n = 23). Furthermore, no association between intensity of pathological changes and genotype was detected. In a farm with a very high prevalence of bovine brucellosis, the percentages of strains of the SSCA(r) genotype were 86 and 84% in serologically positive (n = 64) and negative (n = 36) cows, respectively. Therefore, no association was found between the NRAMP1-resistant allele and the resistant phenotype in either experimental or naturally occurring brucellosis. To further support these results, bacterial intracellular survival was assessed in bovine monocyte-derived macrophages from cattle with either the resistant or susceptible genotype. In agreement with our previous results, no difference was observed in the rates of intracellular survival of B. abortus within macrophages from cattle with susceptible or resistant genotypes. Taken together, these results indicate that these polymorphisms at the NRAMP1 3'UTR do not affect resistance against B. abortus in cattle and that they are therefore not suitable markers of natural resistance against bovine brucellosis.

Rescuing valuable genomes by animal cloning: a case for natural disease resistance in cattle

Tissue banking and animal cloning represent a powerful tool for conserving and regenerating valuable animal genomes. Here we report an example involving cattle and the rescue of a genome affording natural disease resistance. During the course of a 2-decade study involving the phenotypic and genotypic analysis for the functional and genetic basis of natural disease resistance against bovine brucellosis, a foundation sire was identified and confirmed to be genetically resistant to Brucella abortus. This unique animal was utilized extensively in numerous animal breeding studies to further characterize the genetic basis for natural disease resistance. The bull died in 1996 of natural causes, and no semen was available for AI, resulting in the loss of this valuable genome. Fibroblast cell lines had been established in 1985, cryopreserved, and stored in liquid nitrogen for future genetic analysis. Therefore, we decided to utilize these cells for somatic cell nuclear transfer to attempt the production of a cloned bull and salvage this valuable genotype. Embryos were produced by somatic cell nuclear transfer and transferred to 20 recipient cows, 10 of which became pregnant as determined by ultrasound at d 40 of gestation. One calf survived to term. At present, the cloned bull is 4.5 yr old and appears completely normal as determined by physical examination and blood chemistry. Furthermore, in vitro assays performed to date indicate this bull is naturally resistant to B. abortus, Mycobacterium bovis, and Salmonella typhimurium, as was the original genetic donor.

Efficacy of strain RB51 vaccine in heifers against experimental brucellosis

With the goal of providing an additional tool for controlling bovine brucellosis in Brazil and evaluating the full calf dose in adult cattle, the efficacy of the rough Brucella abortus strain RB51 vaccine was tested in heifers. Thirty-three females of approximately 24 months of age were divided in two groups: one group (n=20) received the RB51 vaccine and the other group (n=13) were used as non-vaccinated control. Animals in the vaccinated group were split in two sub-groups. One sub-group (n=12) was vaccinated subcutaneously with 1.5x10(10) colony forming units (CFU) of RB51 at Day 0 of the experiment and the other sub-group (n=8) was vaccinated subcutaneously with 1.6x10(10) CFU of RB51 at 60 days of gestation (Day 260 of the experiment). All cattle were challenged between 6 and 7 months of pregnancy with 3x10(8) CFU of the virulent strain 2308 of B. abortus by the conjunctival route. Vaccination with RB51 vaccine did not result in the production of any antibodies against the O-side chain of lipopolysaccharide (LPS), as measured by conventional serological tests (rose bengal plate agglutination test (RBPAT), standard tube agglutination test (STAT), and 2-mercaptoethanol test (2ME)). A total of 25% cumulative incidence of abortions was found in the vaccinated group, whereas in the control group the cumulative incidence was 62%. B. abortus RB51 was not isolated from any sample, and no abortions were produced by RB51 vaccination of females at 60 days of pregnancy. The results indicate that vaccination with RB51 prevented 59.4% of abortions, 58.6% of cow infections, and 61.0% of fetal infections. The relative risk (RR) revealed that non-vaccinated animals have 2.462 (95% CI 1.029-5.889) times higher risk of aborting than RB51-vaccinated animals.

Lack of association of brucellosis resistance with (GT)13 microsatellite allele at 3′UTR of NRAMP1 gene in Indian zebu (Bos indicus) and crossbred (Bos indicus×Bos taurus) cattle

Natural resistance associated macrophage protein 1 (NRAMP1), an integral transmembrane protein, is reported to influence the intraphagosomal microbial replication and thereby confer resistance to several intracellular pathogens in mice. In bovine, a significant association of (GT)(13) allelic variant of polymorphic microsatellite at 3' untranslated region (UTR) of NRAMP1 gene with natural resistance to brucellosis has been established. The present study was aimed to detect polymorphism at 3'UTR of NRAMP1 gene in Hariana breed of Bos indicus cattle and Holstein Friesian crossbred (B. indicusxBos taurus) cattle, and to determine the association of this polymorphism with resistance/susceptibility to brucellosis. The (GT)(n) polymorphism at 3'UTR in terms of variation in fragment length was determined using denaturing polyacrylamide gel analysis of radioisotope incorporated amplicon of 174 bp. Screening of a total of 100 samples (comprising 50 random samples of each breed) revealed that animals were of same genotype, i.e., homozygous (GT)(13)/(GT)(13). Sequencing of amplicons from representative animals confirmed the presence of (GT)(13) repeat. For association study, the animals that were positive in all three serological tests (viz., RBPT, STAT and ELISA) and had history of abortion were grouped as "affected"; whereas the animals that were negative in all these tests and completed third lactation without any history of abortion were grouped as "non-affected". Since, all animals belonging to either group were homozygous (GT)(13), association could not be established. However, the present study demonstrated that the presence of (GT)(13) allele even in homozygous condition could not provide enough resistance to brucellosis in a naturally infected herd.

Frequency of bovine Nramp1 (Slc11a1) alleles in Holstein and Zebu breeds

Natural resistance against brucellosis in cattle is linked to the Nramp1 gene, which encodes a divalent cation transporter that localizes in the phagolysosome membrane in macrophages. Nramp1 gene in mouse plays a critical role in innate immunity favoring bacterial killing by macrophages in addition to its influence on adaptative immunity. Polymorphisms at the bovine Nramp1 3' untranslated region (3'UTR), detectable by Single Strand Conformational Analysis (SSCA), are associated with natural resistance against brucellosis. Such polymorphisms are associated with variation in the number of GT repeats. This study compared the frequency of Nramp1 3'UTR polymorphisms between Zebu and European bovine breeds. Eighty-one Holsteins (Bos taurus taurus) and 167 Zebu (Bos taurus indicus), including the following breeds: Nelore (n=95), Guzerá (n=37), and Gir (n=35), totaling 248 pure breed cattle studied. DNA extraction was performed using the guanidium protocol and genotyping was performed by SSCA. DNA from cattle considered genotypically resistant to brucellosis resulted in a single band (homozygous) with 175bp, corresponding to the 3'UTR with 13 GT pairs (GT13), whereas DNA from genotypically susceptible cattle generated one single band with 177bp (homozygous GT14) or double bands with both 175 and 177bp, or 175 and 179bp (heterozygous GT13/GT14 or GT13/GT15, respectively). A marked difference in the frequency of alleles was detected between the Zebu and Holstein cattle. Holsteins had an extremely homogeneous genotype, with 100% of the individuals with a GT13 genotype. In sharp contrast the Nelore breed had the most heterogeneous genotype with four allelic combinations, namely, homozygous GT13, homozygous GT14, heterozygous GT13/GT14, and heterozygous GT13/GT15. When the Zebu breeds were compared to each other, the only significant difference observed was the frequencies of the genotypes GT13 and GT14 between the Nelore and Guzerá breeds. The knowledge of allelic frequencies in different breeds of cattle may prove to be very useful in the future for planning breeding strategies for selection of resistant cattle.

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

The fluorescence polarisation assay (FPA) is a recently described test for the serological diagnosis of Brucella infection. It has many methodological advantages over older, more established tests and can be performed in a fraction of the time. To validate the FPA, serum samples from 146 confirmed (by culture) Brucella-infected cattle were tested in conjunction with serum samples from 1947 noninfected cattle. The competitive ELISA (cELISA) was validated using these positive reference samples and 1440 negative samples, while data for the indirect ELISA (iELISA) was generated from 6957 negative samples plus the positive sera. Published diagnostic specificity (DSp) data for the complement fixation test (CFT) and serum agglutination test (SAT) was used in conjunction with the test results on the positive sera to obtain diagnostic specificity plus diagnostic sensitivity (DSn). After selection of a cutoff for the FPA and cELISA, the diagnostic specificity and sensitivity total for each test were compared. The results, with 95% confidence intervals, were: FPA (195.7+/-2.79), iELISA (195.0+/-2.70), cELISA (194.9+/-3.48), CFT (191.7+/-4.45), and SAT (180.4+/-6.33). The data presented supports the use of the FPA in diagnosis of brucellosis and questions the use of the SAT and CFT for either screening or confirmatory testing.

Enzyme-linked immunosorbent assay to differentiate the antibody responses of animals infected with Brucella species from those of animals infected with Yersinia enterocolitica O9

Enzyme-linked immunosorbent assays using antigens extracted from Brucella abortus with n-lauroylsarcosine differentiated natural Brucella-infected animals from Brucella-vaccinated or Yersinia enterocolitica O9-infected animals. A field trial in Mongolia showed cattle, sheep, goat, reindeer, camel, and human sera without infection could be distinguished from Brucella-infected animals by conventional serological tests.

Evaluation of brucellosis RB51 vaccine for domestic water buffalo (Bubalus bubalis) in Trinidad

Thirty-two young domestic water buffalo (Bubalus bubalis) were obtained from a brucellosis-free farm to determine effectiveness of RB51 vaccination for prevention of Brucella infection under natural-exposure conditions in Trinidad. Study animals (20 males and 12 females 5-20 months old) were assigned to vaccination or control groups, using a block randomization design ensuring equal sex distributions between groups. The vaccination group received commercially available RB51 at the recommended calfhood dose of (1.0-3.4)x10(10) colony-forming units (CFU) and controls received 2ml sterile saline. Vaccination did not result in positive serologic results as measured by four traditional agglutination tests: standard tube agglutination test (STAT), standard plate agglutination test (SPAT), buffered plate agglutination test (BPAT), and card agglutination. Study animals were maintained in a brucellosis-positive herd in southern Trinidad with an estimated 56% prevalence to allow for natural exposure to B. abortus, which was evaluated using STAT, SPAT, BPAT, and card tests. Animals were sampled seven times over 2 years and were classified as positive if they had persistent agglutination titers or had Brucella isolated from specimens collected at completion of the study. Five of the original 32 study animals were lost to follow-up during the field trial. Six of the 14 (43%) vaccinated animals completing the study were classified as positive for Brucella infection-as were two of the 13 (15%) control animals (P=0.21). Isolates from four vaccinates and one control were confirmed as B. abortus biovar 1.

Bovine T lymphocyte responses to Brucella abortus

The long-held paradigm of T lymphocyte-mediated activation of mononuclear phagocytes (Mø) as the major mechanism of protection against facultative intracellular pathogens such as Brucella has been modified to include killing of infected Mø by various subsets of T lymphocytes. Remnants of killed infected cells are phagocytosed by immunologically-activated Mø, which are much more efficient at killing such pathogens. Most of the detailed information regarding immunity in general and that of brucellosis specifically has been obtained using murine infection models rather than in cattle. However, there has been considerable definition of cellular phenotypes, cytokines and functional characteristics of T lymphocytes in cattle over the last decade. This was mainly due to development of monoclonal antibodies against cell surface markers and application of molecular cloning and polymerase chain reaction (PCR) for isolation, characterization and detection of genes encoding bovine cytokines. This review discusses cellular and molecular immunity in bovine brucellosis as pertains to T lymphocyte interactions with the Mø. Although current knowledge directly obtained from brucellosis immunity studies in the bovine host is limited and incomplete, the many parallels between the bovine and murine immune systems allow for some extrapolation in the description of bovine host defense mechanisms. Direct information from studies with immunized cattle supports the concepts of coordinate activation of uninfected Mø and killing of Brucella-infected Mø by antigen-specific T lymphocytes as major mechanisms of host defense in bovine brucellosis. There also appears to be a bias in the T lymphocyte compartment towards recognition of particular bacterial stress proteins following immunization with live Brucella vaccines.

How to substantiate eradication of bovine brucellosis when aspecific serological reactions occur in the course of brucellosis testing

Collaborative work was financed by the EU to develop and assess new diagnostic tools that can differentiate between bovine brucellosis and bovine infections due to Yersinia enterocolitica O:9 either in conjunction with, or as an alternative to, the classical serological, bacteriological or allergic skin tests. Sixteen heifers were experimentally infected with Brucella abortus biovar 1 (five heifers), Brucella suis biovar 2 (two heifers), Y. enterocolitica O:9 (six heifers) and Y. enterocolitica O:3 (three heifers). Four heifers, naturally infected with Y. enterocolitica O:9 that presented aspecific brucellosis serological reactions were also included in the experiment. A self-limited infection was induced in cattle by B. suis biovar 2. All the brucellosis serological tests used, i.e. the slow agglutination test (SAW), the Rose Bengal test (RB), the complement fixation test (CFT), indirect and competitive ELISA's, lacked specificity when used to analyze sera from Y. enterocolitica O:9 infected animals. A Yersinia outer membrane proteins (YOPs)-ELISA was also used and although the test is able to detect a Yersinia group infection, it provided no evidence of whether or not there is a possible brucellosis infection when dual infections are present. The brucellergen IFN-gamma test showed a lack of specificity also. The only test that was proven to be specific is the brucellergen skin test. All brucellosis serological tests, except the indirect ELISA, were limited in their ability to detect B. abortus persistently infected animals. Based on these experimental studies, a strategy was implemented as part of the year 2001 Belgian Brucellosis Eradication Program to substantiate the eradication of bovine brucellosis. Epidemiological inquiries have identified risk factors associated with aspecific serological reactions, possible transmission and infection of cattle by B. suis biovar 2 from infected wild boars; and both legal and administrative measures taken by the veterinary services. No cases of bovine brucellosis have been confirmed in Belgium since March 2000.

Brucella abortus RB51: enhancing vaccine efficacy and developing multivalent vaccines

Brucella abortus vaccine strain RB51 is an attenuated, stable rough mutant that is being used in many countries to control bovine brucellosis. Our earlier study demonstrated that the protective efficacy of strain RB51 can be significantly enhanced by overexpressing Cu-Zn superoxide dismutase (SOD), a homologous protective antigen. We have also previously demonstrated that strain RB51 can be engineered to express heterologous proteins and mice vaccinated with such recombinant RB51 strains develop a strong Th1 type of immune response to the foreign proteins. The present study is aimed at combining these two characteristics to generate new recombinant RB51 vaccines with enhanced abilities to protect against brucellosis and simultaneously able to protect against infections by Mycobacterium spp. We constructed two recombinant RB51 strains, RB51SOD/85A which overexpresses SOD with simultaneous expression of the 85A, a protective protein of Mycobacterium spp., and RB51ESAT which expresses ESAT-6, another protective protein of M. bovis, as a fusion protein with the signal sequence and few additional amino terminal amino acids of SOD. Mice vaccinated with these recombinant strains developed specific immune responses to the mycobacterial proteins and significantly enhanced protection against Brucella challenge compared to the mice vaccinated with strain RB51 alone.

Brucellosis vaccines: past, present and future

The first effective Brucella vaccine was based on live Brucella abortus strain 19, a laboratory-derived strain attenuated by an unknown process during subculture. This induces reasonable protection against B. abortus, but at the expense of persistent serological responses. A similar problem occurs with the B. melitensis Rev.1 strain that is still the most effective vaccine against caprine and ovine brucellosis. Vaccines based on killed cells of virulent strains administered with adjuvant induced significant protection but also unacceptable levels of antibodies interfering with diagnostic tests. Attempts were made to circumvent this problem by using a live rough strain B. abortus 45/20, but this reverted to virulence in vivo. Use of killed cells of this strain in adjuvant met with moderate success but batch to batch variation in reactogenicity and agglutinogenicity limited application. This problem has been overcome by the development of the rifampicin-resistant mutant B. abortus RB51 strain. This strain has proved safe and effective in the field against bovine brucellosis and exhibits negligible interference with diagnostic serology. Attempts are being made to develop defined rough mutant vaccine strains that would be more effective against B. melitensis and B. suis. Various studies have examined cell-free native and recombinant proteins as candidate protective antigens, with or without adjuvants. Limited success has been obtained with these or with DNA vaccines encoding known protective antigens in experimental models and further work is indicated.

Molecular and cellular interactions between Brucella abortus antigens and host immune responses

Host protection against Brucella abortus, is thought to be mediated primarily by a Th1 type immune response. Unfortunately, only few specific bacterial antigens involved in stimulating protective cellular immunity against Brucella are known. Therefore, identifying bacterial proteins that induce a T-lymphocyte mediated response is critical to determine Brucella immunity. Several library screening methods are discussed that have been used to identify Brucella proteins that stimulate T lymphocytes including cellular immunoblotting, Escherichia coli expressed Brucella proteins, green fluorescence reporter systems, and signature tagged mutagenesis. Future studies would likely examine how bacterial proteins expressed within host cells aid pathogen survival and/or induce host responses. Some of these newly identified bacterial gene products may serve as antigens to activate a protective host immune response. Also, identifying Brucella proteins expressed at particular times during infection will also yield insights into Brucella pathogenesis.

Paradigm shifts in vaccine development: lessons learned about antigenicity, pathogenicity and virulence of Brucellae

As part of a program to support the USDA Animal Plant Health Inspection Service Bovine Brucellosis Eradication Program, the Brucellosis Research Unit of the National Animal Disease Center (NADC) sought to develop a bovine brucellosis vaccine that would allow vaccinated animals to be distinguished from virulent field infected animals. In order to meet that goal, several avenues of research were undertaken to construct and test candidate vaccines, including Brucella abortus RB51. In early vaccine development studies, a subunit preparation obtained by extracting B. abortus with salts was studied as a candidate subunit vaccine. Later, molecular biological techniques were used both to clone genes encoding products found in the salt extract (BCSP31 and Cu-Zn SOD) and genes encoding proteins of B. abortus that were antigenic (HtrA) or possibly essential (two-component systems) for full virulence of B. abortus. In vitro systems using mammalian cells lines such as HeLa and macrophage-related were used along with the mouse model and host animal models. Results obtained at NADC and in other Brucellosis research laboratories, using survival in mammalian cell lines and the mouse model to access pathogenicity and virulence of genetically engineered strains, do not necessarily identify loci that are essential for full virulence or pathogenicity in the natural host, the bovine. Studies at NADC and other brucellosis laboratories showed that antigenicity was not a predictor of the effectiveness of a protein as a subunit vaccine.

Molecular and immunological characterisation of recombinant Brucella abortus glyceraldehyde-3-phosphate-dehydrogenase, a T- and B-cell reactive protein that induces partial protection when co-administered with an interleukin-12-expressing plasmid in a DNA vaccine formulation

To identify antigens of Brucella spp. that are potentially involved in stimulating a protective T-cell-mediated immune response, previous studies identified 10 clones from a Brucella abortus 2308 genomic library with primed lymphocytes as probes. One selected positive clone (182) contained an insert of 1.2 kb which was identified, sequenced and characterised. The deduced amino acid sequence of the open reading frame (ORF) revealed 82% and 81% identity to the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) enzymes from Agrobacterium tumefaciens and Xanthobacter flavus, respectively. Southern blot analysis demonstrated that the gap gene is present in only one copy in the Brucella genome. B. abortus GAPDH was then expressed in Escherichia coli as a fusion protein with the maltose-binding protein (MBP). To demonstrate the functional activity of Brucella GAPDH, E. coli gap mutants were transformed with a Brucella pMAL-gap construct. Genetic complementation was achieved and as a result E. coli mutants were able to grow on glucose or other carbon source medium. The humoral and cellular immune responses to the recombinant (r) GAPDH were characterised. In Western blots, sera from naturally infected cattle and sheep showed antibody reactivity against rGAPDH. In response to in-vitro stimulation by rGAPDH, splenocytes from mice vaccinated with rGAPDH or B. abortus S19 were able to produce gamma-interferon and tumour necrosis factor-a but not interleukin (IL)-4. Furthermore, gap associated with murine IL-12 gene in a DNA vaccine formulation partially protected mice against experimental infection.

Brucella abortus vaccine strain RB51 produces low levels of M-like O-antigen

Brucella abortus RB51 is a rough (R) stable vaccine strain used in cattle and is believed to be devoid of O-side chain. We analyzed by use of a panel of monoclonal antibodies (MAbs) directed against seven previously defined O-polysaccharide (O-PS) epitopes the O-chain expression in strain RB51. Two MAbs specific for the C/Y (A=M) and C (M>A) epitopes showed low bindings in ELISA to strain RB51. O-chain expression was further confirmed by Western blot after SDS-PAGE of strain RB51. In particular, the MAb of C (M>A) specificity, showing preferential binding to M-dominant smooth (S) Brucella strains, revealed in strain RB51 a typical smooth-lipopolysaccharide (S-LPS) pattern which resembled that of M-dominant S-LPS. Thus, the results clearly show that strain RB51 produces low levels of M-like O-antigen.

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.

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.

The effect of Brucella abortus on hydrogen peroxide and nitric oxide production by bovine polymorphonuclear cells

The effect of Brucella on the generation of microbicidal reactive oxygen and nitrogen metabolites by bovine peripheral polymorphonuclear cells (PMNs) was investigated. The PMNs were recovered from the peripheral blood of control calves and experimental calves previously vaccinated against brucellosis. Significantly larger quantities of NO and H2O2 were generated by PMNs from control and experimental calves following activation by heat-killed whole cells or outer membrane protein of Brucella abortus than by non-activated cells (p<0.05-0.01). In contrast, generation of H2O2 and NO decreased when PMNs were exposed to the lipopolysaccharide of Brucella. However, the generation of H2O2 and NO by activated PMNs from the control and experimental calves did not differ significantly.

Comparison of the antibody response in adult cattle against different epitopes of Brucella abortus lipopolysaccharide

The comparison of serological responses in a sample of adult, vaccinated and held-infected bovines with Brucella abortus is reported. Indirect enzyme immunoassav (EIA) titration curves and Western blotting tests for smooth-type lipopolysaccharide (S-LPS), rough-type LPS (R-LPS) and lipid A were performed. In the initial screening of sera, an overall prevalence of 20.5% was found, which corresponds to a country with a high incidence of brucellosis. End-point EIA titres against LPS antigens from vaccinated and field-infected cows were not significantly different. However, the absorbance values in the titration curves were significantly higher for S-LPS as compared with the other antigens. A high correlation coefficient (r = 0.933) was obtained when the titres to R-LPS versus lipid A were compared. Western blotting reactions of vaccinated and held-infected animals were indistinguishable. S-LPS, R-LPS and lipid A epitopes were recognized in a heterogeneous manner. In general, the number of bovines that reacted against LPS was higher in the field-infected group, with a stronger binding to S-LPS. Based on our observations, the vaccinated and field-infected bovines are capable of producing similar antibody responses to the Brucella main outer surface antigen, LPS. It should be emphasized that the humoral response of cattle to Brucella LPS contains significant amounts of antibodies to other antigenic moieties of this important surface molecule, which may contribute to the immunity to brucellosis.

Use of detergent extracts of Brucella abortus RB51 to detect serologic responses in RB51-vaccinated cattle

Serologic responses to the newly introduced rough Brucella abortus vaccine strain RB51 have been determined in a dot-blot format using gamma-irradiated RB51 cells as the antigen. Because gamma-irradiated cells are not easily prepared and the signal from cells was not always reliable, an alternative antigen was sought. Detergent extracts of B. abortus RB51 were prepared using zwittergent 3-14, Triton X-100, and sodium dodecyl sulfate (SDS) and examined in a dot-blot format. Zwittergent 3-14 extracts and gamma-irradiated RB51 cells gave the same titers. Unlike gamma-irradiated RB51 cells, zwittergent 3-14 extracts produced signals consistently, and the signals were easily interpreted. Triton X-100 extracts interfered with signal development, and SDS extracts resulted in a high background signal. Western blot analyses revealed several outer membrane proteins in the zwittergent 3-14 extract. The major antigens in the extract had apparent molecular weights of <20,000.

Seroconversion and abortion in cattle experimentally infected with Brucella sp. isolated from a Pacific harbor seal (Phoca vitulina richardsi)

Previously unrecognized Brucella species have been isolated from a number of marine mammals, including harbor seals (Phoca vitulina richardsi) in the Puget Sound area of the state of Washington. Because of the presence of dairy herds in proximity to the harbor seal populations, a study was conducted to determine the effects of the harbor seal Brucella isolate in experimentally inoculated cattle. Six pregnant cattle were exposed by intravenous injection (n = 3) or intraconjunctival inoculation (n = 3). Two pregnant cows were intravenously injected with saline and served as controls. All of the cows receiving the Brucella seroconverted on 1 or more tests commonly used for the detection of Brucella abortus infection. Two of the cattle receiving the intravenous inoculation aborted, and brucellae were demonstrated in the fetuses and dams immediately following abortion. The remaining 4 Brucella-inoculated animals and their fetuses were culture negative for the organism at 14 weeks postinoculation. Results of this study indicate the marine mammal Brucella is capable of producing seroconversion and abortion in cattle but is less pathogenic in that species than B. abortus.

Field validation of the use of RB51 as antigen in a complement fixation test to identify calves vaccinated with Brucella abortus RB51

In order to confirm the efficiency of an experimental RB51-based complement fixation (CF) test in identifying cattle vaccinated with Brucella abortus strain RB51, 831 sera from 110 vaccinated and 48 unvaccinated Hereford heifers of Iowa, collected for studies conducted in different years, were sent to Italy without coding to be tested in a CF test using RB51 as antigen. Most of the calves, aged from 3 to 10 months, were vaccinated subcutaneously with the recommended dosage of 10(10) CFU of RB51 commercial vaccine, while only six calves received 10(9) CFU of the same vaccine. Serum samples for serologic testing, collected until 16 postinoculation weeks (PIW), were also tested by routine surveillance tests for brucellosis such as rose bengal plate and CF tests performed with B. abortus smooth strain 99 as control antigen. RB51 CF test results obtained by testing sera from cattle vaccinated in 1999 indicate that the sensitivity of the reaction is 97% at 2 to 3 PIW and 90% until 8 PIW and decreases to 65% at 12 PIW, the specificity remaining at 100%. Collectively, the results of this study confirm that serologic standard tests fail to detect antibodies to RB51 while the RB51-based CF test is able to monitor antibody responses to RB51 until 15 to 16 PIW with a specificity of 100%. In addition, unlike the RB51-based dot blot assay, which is the only test currently used to monitor antibody responses to RB51, the CF test also detected specific responses following vaccination with 10(9) CFU of RB51, although seroconversion was only 50% at 8 PIW. In conclusion, because of high specificity and sensitivity, the CF test described here can be used to efficaciously monitor serologic responses following RB51 vaccination in cattle and could also be employed to detect RB51 infection in humans exposed to this strain.

Development, testing and commercialization of a new brucellosis vaccine for cattle

Vaccines used against brucellosis do not generally protect completely against infection or abortion. Genetic analysis has revealed differences in arrangements of DNA sequences between these vaccine strains and the virulent parent strain and permits the specific identification of field isolates of B. abortus as wild-type or vaccine strain. B. abortus strain 19 is a low-virulence, live vaccine developed for use in cattle. Although it is effective, strain 19 vaccine had a tropism for the placenta and caused abortion when given to pregnant cows, was infectious for humans, and caused serologic responses in calves that could not be differentiated from those in cattle infected with natural field strains. In the mid-1980s the need for a new vaccine emerged when the USDA increased its efforts in brucellosis eradication. In the 1990s, research on biosafety, vaccine efficacy and field application rapidly established the fact that strain RB51 is protective in cattle at doses comparable to those of strain 19. Thus, Brucella abortus strain RB51 is the vaccine of choice against brucellosis of cattle in the United States. Studies have established the relative efficacy of strain RB51 vaccine on bison, and the vaccine has also been accepted for use in commercial bison herds in the U.S.

Pathology of brucellosis in bison from Yellowstone National Park

Between February 1995 and June 1999, specimens from seven aborted bison (Bison bison) fetuses or stillborn calves and their placentas, two additional placentas, three dead neonates, one 2-wk-old calf, and 35 juvenile and adult female bison from Yellowstone National Park (USA) were submitted for bacteriologic and histopathologic examination. One adult animal with a retained placenta had recently aborted. Serum samples from the 35 juvenile and adult bison were tested for Brucella spp. antibodies. Twenty-six bison, including the cow with the retained placenta, were seropositive, one was suspect, and eight were seronegative. Brucella abortus biovar 1 was isolated from three aborted fetuses and associated placentas, an additional placenta, the 2-wk-old calf, and 11 of the seropositive female bison including the animal that had recently aborted. Brucella abortus biovar 2 was isolated from one additional seropositive adult female bison. Brucella abortus was recovered from numerous tissue sites from the aborted fetuses, placentas and 2-wk-old calf. In the juvenile and adult bison, the organism was more frequently isolated from supramammary (83%), retropharyngeal (67%), and iliac (58%) lymph nodes than from other tissues cultured. Cultures from the seronegative and suspect bison were negative for B. abortus. Lesions in the B. abortus-infected, aborted placentas and fetuses consisted of necropurulent placentitis and mild bronchointerstitial pneumonia. The infected 2-wk-old calf had bronchointerstitial pneumonia, focal splenic infarction, and purulent nephritis. The recently-aborting bison cow had purulent endometritis and necropurulent placentitis. Immunohistochemical staining of tissues from the culture-positive aborted fetuses, placentas, 2-wk-old calf, and recently-aborting cow disclosed large numbers of B. abortus in placental trophoblasts and exudate, and fetal and calf lung. A similar study with the same tissue collection and culture protocol was done using six seropositive cattle from a B. abortus-infected herd in July and August, 1997. Results of the bison and cattle studies were similar.

Survival of Brucella abortus strain RB51 lyophilized and as liquid vaccine under different storage conditions

Brucella abortus strain RB51 (SRB51) is a new cattle vaccine that is approved for use in the U.S. for prevention of brucellosis. At the present time, other countries are implementing or considering the use of SRB51 vaccine in their brucellosis control programs. In the current study, the effect of three stabilizing media, two fill volumes (1 and 3 ml), and three storage temperatures (-25, 4 and 25 degrees C) on the viability of lyophilized SRB51 over a 52 week period was determined. The effects of three concentrations of bacteria (5 x 10(8), 1 x 10(9), or 5 x 10(9) cfu/ml) and two storage temperatures (4 or 25 degrees C) on viability of liquid SRB51 vaccine were also determined. For lyophilized strain RB51 vaccine, fill volume did not influence viability (P> 0.05) during lyophilization. Although fill volume did not influence viability during storage in World Health Organization (WHO) media or media containing both WHO and Lactose Salt (LS) media, 1 ml fill volumes of SRB51 in LS media had greater (P< 0.05) viability when compared to 3 ml fill volumes. Lyophilized SRB51 vaccine stored at 25 degrees C had a more rapid decline in viability (P< 0.05) when compared to vaccine stored at -25 or 4 degrees C. With the exception of the 3-ml fill volumes of LS media, all three stabilizing media were similar in maintaining viability of SRB51 at -25 degrees C storage temperatures. However, when compared to WHO or WHO/LS media, stabilization in LS media was associated with a more rapid decline in viability during storage at 4 or 25 degrees C (P< 0.05). Initial SRB51 concentration in liquid vaccine did not influence (P> 0.05) viability during storage at 4 or 25 degrees C. When compared to liquid SRB51 vaccine stored at 25 degrees C, storage at 4 degrees C was associated with a slower decline in viability (P< 0.05) during 12 weeks of storage. Biochemical and morphological characteristics of SRB51 were stable under the storage conditions utilized in the present study. This study suggests that viability of SRB51 can be readily maintained during storage as a lyophilized or liquid brucellosis vaccine.

Response of Bali cattle (Bos javanicus) to vaccination with Brucella abortus strain 19 in West Timor

A trial was conducted in two villages (one containing cattle infected with brucellosis and one not containing infected cattle) in Timor, Indonesia to determine the serological response to vaccination with Brucella abortus strain 19 in Bali cattle (Bos javanicus) (n = 599). Mature female cattle were immunised with low-dose strain 19 (2x10(8)-6x10(8) colony forming units) and calves (6-12 months) with high-dose strain 19 (4x10(10)-12x10(10) colony forming units). Other mature females and calves were inoculated with sterile vaccine diluent and formed a non-vaccinated in-contact control group. The seroprevalence and mean titres were highest in the vaccinated cattle 3 months after vaccination. These then receded, however, 1% of vaccinated calves and 1.9% of vaccinated cows from the village without infected cattle were still seropositive on the complement-fixation test (CFT) 24 months after vaccination. Non-vaccinated seropositive animals were more likely to have aborted or had a stillbirth and were less likely to have produced a calf than were seronegative cows from the village containing infected animals. We concluded that strain 19 vaccine induced protection in Bali cattle and that this vaccine might play an important role in the control of bovine brucellosis in Timor.

Attenuation and immunogenicity of a Brucella abortus htrA cycL double mutant in cattle

PHE1 is a htrA cycL double gene deletion mutant of virulent Brucella abortus strain 2308 (S2308) which has previously been evaluated in the murine and caprine models of bovine brucellosis. This report describes the results of studies conducted with this mutant in the natural bovine host. Six sexually mature, non-gravid heifers were inoculated via the conjunctival sac with 1 x 10(10) colony forming units (CFU) of either the parental S2308 or the htrA cycL gene deletion mutant, PHE1. At 4, 7 and 11 days post-inoculation, PHE1 was found to colonize the bovine host at lower levels than S2308. In a second experiment, eight heifers in mid-gestation were infected with 1 x 10(7) CFU of either strain via the conjunctival sac. The virulent S2308 caused abortions or weak calves in 4/4 cows, while all four cows infected with PHE1 had healthy calves. Furthermore, PHE1 exhibited decreased resistance to killing by cultured bovine neutrophils and macrophages compared to the parental strain. These studies demonstrate that the B. abortus htrA cycL gene deletion mutant PHE1 is highly attenuated in the bovine host when compared to the virulent parental S2308.

Cloning and kinetics of expression of Brucella abortus heat shock proteins by baculovirus recombinants

In an effort to develop genetically engineered Brucella abortus (BA) vaccines, the genes encoding heat shock proteins (HSPs) GroEL, GroES, and HtrA were cloned and expressed in the BAC-TO-BAC Baculovirus System, and the kinetics of protein expression were analyzed using various insect cell lines in suspension cultures, different cell densities in suspension cultures, multiplicities of infection and recombinant virus replication times. Trichoplusia ni cells expressed only BA HtrA, but Spodoptera frugiperda (Sf9) cells expressed all three recombinant proteins. The best GroEL expression was achieved by infecting 2x10(6) Sf9 cells/ml with an MOI 10 of recombinant virus and harvesting the cells after 96h of virus replication. GroES and HtrA were best expressed when infecting 2x10(6) Sf9 cells/ml with an MOI 1 of recombinant viruses and harvesting the cells after 120h of virus replications. Under these conditions BA recombinant HSPs were expressed as follows: GroEL at 16% of the total cellular proteins (105microg/ml concentration); GroES 2% (15.25microg/ml); and HtrA 8% (84.48microg/ml). This is the first report of cloning and expression of BA genes in the baculovirus system.

HSP and apoptosis in leukocytes from infected or vaccinated animals by Brucella abortus

The production of hsp and apoptosis of leukocytes in the peripheral blood of animals naturally infected with Brucella spp or treated with the vaccine Brucella abortus 19 have been investigated in this study. Cytokines able to induce phagocytic activity in macrophages of non treated healthy animals were found in the supernatant of bovine leukocytes cultivated in vitro. A long-lasting antibody response against hsp 60 kDa and 27 kDa, which lasts a long time, is induced in naturally infected animals, while in animals vaccinated with B. abortus 19 we detected an antibody response against hsp 60 and 70 kDa which is much shorter, disappearing in two months. During the early phase of infection, lymphocytes and monocytes of naturally infected animals show a delay of apoptosis in vitro compared to the same cells coming from healthy controls and vaccinated animals.

Use of Brucella abortus vaccine strain RB51 in pregnant cows after calfhood vaccination with strain 19 in Argentina

One hundred and seven pregnant cows, which had been calfhood vaccinated with Brucella abortus strain 19 (S-19) were revaccinated with either S-19 or strain RB51 (S-RB51). All S-19-revaccinated animals seroconverted, while none of the RB51-revaccinated animals seroconverted. Two out of 25 (8%) S-19-revaccinated animals aborted, while none of the 57 RB51-revaccinated group aborted. Four of the S-19-revaccinated animals shed S-19 in the milk for at least 7 days, while only 1 cow shed S-RB51 for at least 3 days (but <7 days) post-parturition. Revaccination of strain 19 calfhood-vaccinated, pregnant cattle with S-RB51 appears to be a safe procedure with no diagnostically negative consequences.

Complement fixation test to assess humoral immunity in cattle and sheep vaccinated with Brucella abortus RB51

The live attenuated Brucella abortus strain RB51 is a rifampin-resistant, lipopolysaccharide (LPS) O-chain-deficient mutant of virulent B. abortus 2308. The reduced O-chain content in RB51 prevents this bacterium from inducing antibodies detectable by the conventional serologic tests for bovine brucellosis diagnosis that mainly identify antibodies to LPS. The absence of available serologic tests for RB51 also complicates the diagnosis of possible RB51 infections in humans exposed to this strain. The purpose of this study was to evaluate the suitability of a complement fixation (CF) test performed with the rough strain B. abortus RB51, previously deprived of anticomplementary activity, in detecting anti-B. abortus RB51 antibodies in cattle and sheep experimentally vaccinated with this strain. The results of this study showed that a CF test with RB51 as the antigen is able to specifically detect antibodies following RB51 vaccination in cattle and sheep. In addition, this method could be a useful tool for detecting B. abortus RB51 infection in humans.

Mechanism of serum resistance among Brucella abortus isolates

It was shown in this study that complement-resistant Brucella abortus used were unable to activate complement in the absence of specific antibody. Complement-resistant isolates possessed O-antigen, but complement-sensitive organisms used are O-antigen deficient. Since B. abortus LPS does not activate the alternative pathway of complement, we concluded that activation of bovine complement must be due to some other mechanism. In this study, it was shown that bovine C1 binds to the outer membrane proteins of B. abortus. Isolated outer membrane proteins of both smooth (O-antigen positive) and rough (O-antigen negative) B. abortus used bind to C1q. However, only rough isolates were killed by complement. All of the O-antigen positive B. abortus isolates were complement-resistant. We propose that O-antigen shields outer membrane proteins and blocks C1q binding.

Diagnosis of bovine brucellosis by skin test: conditions for the test and evaluation of its performance

Brucellergene OCB (Rhône-Mérieux) was used as an allergen to define the intrinsic parameters of a skin test and to compare its properties with serology for the diagnosis of bovine brucellosis. The skin test was also evaluated for its capacity to solve problems associated with false positive reactions in serological tests. The optimal reading delay for the skin test was 72 hours. The brucellosis allergic reaction was two to three times less intense than the tuberculosis allergic reaction. An increase of 1.1 mm or more in the skin thickness was therefore considered to be an adequate cut-off. The specificity calculated for 1192 brucellosis-free animals (including animals from brucellosis-free herds in which false positive serological reactions had been reported) was 99-83 per cent (95 per cent confidence interval [CI] 99-40 to 99-98 per cent). The sensitivity determined from 27 experimentally infected heifers ranged from 93 per cent (95 per cent CI 76 to 100 per cent) to 78 per cent (95 per cent CI 58 to 91 per cent) when measured respectively one and six months after the infection. Allergic reactions could be detected in vaccinated animals up to four-and-a-half years after the vaccination. On the other hand, no sensitisation was recorded in naïve animals after up to eight monthly injections of the allergen. The skin test gave valuable information, in combination with the serological tests, in both acute and chronic brucellosis. The skin test discriminated brucellosis clearly from false positive serological reactions due to infections with Yersinia enterocolitica O9.

Biosafety of Brucella abortus strain RB51 for vaccination of mature bulls and pregnant heifers

OBJECTIVE

To determine shedding and colonization profiles in mature sexually intact bulls and pregnant heifers after vaccination with a standard calfhood dose of Brucella abortus strain RB51 (SRB51).

ANIMALS

6 sexually mature 3-year-old Jersey bulls and 7 mixed-breed heifers in midgestation.

PROCEDURE

Bulls and pregnant heifers were vaccinated IM with the standard calfhood dose of 3x10(10) colony-forming units of SRB51. After vaccination, selected body fluids were monitored weekly for vaccine organism shedding. Pathogenesis was monitored in bulls by weekly breeding soundness examination and, in heifers, by delivery status of the calf. Vaccine organism colonization was assessed by obtaining select tissues at necropsy for bacterial culture. Serologic analysis was performed by use of numerous tests, including complement fixation, an SRB51-based ELISA, and immunoblot analysis.

RESULTS

After vaccination, none of the vaccinated bulls or heifers shed SRB51 in their secretions. Results of breeding soundness examination for bulls were normal as was delivery status of the pregnant heifers (6 live births, 1 dystocia). At necropsy, SRB51 was not recovered from any of the selected tissues obtained from bulls, heifers, or calves; however, serologic analysis did detect SRB51-specific antibodies in all cattle.

CONCLUSIONS AND CLINICAL RELEVANCE

Vaccination with the standard calfhood dose of SRB51 administered IM was not associated with shedding or colonization in sexually mature bulls or pregnant heifers. Also, under conditions of this study with small numbers of animals, IM vaccination with SRB51 does not appear to cause any reproductive problems when administered to sexually mature cattle.

Responses of cattle to two dosages of Brucella abortus strain RB51: serology, clearance and efficacy

A new brucellosis vaccine, Brucella abortus strain RB51 (SRB51), is currently recommended for use as a calfhood vaccine in the US at dosages between 1 x 10(10)and 3.4 x 10(10)colony-forming units (CFU). The purpose of the study reported here was to compare responses to minimal and maximal recommended SRB51 dosages. Eighteen heifer calves were vaccinated subcutaneously with 1.6 x 10(10)CFU of SRB51, 3.2 x 10(10)CFU of SRB51, or saline (n = 6 per treatment). The vaccine strain was recovered from the superficial cervical lymph node 14 weeks after vaccination in two of six animals that received 1.6 x 10(10)CFU SRB51, but not from any cattle vaccinated with 3.2 x 10(10)CFU SRB51. The higher SRB51 dosage stimulated greater antibody titres. Protection against abortion or infection following B. abortus strain 2308 (S2308) challenge was similar for both SRB51 dosages and greater than resistance of non-vaccinates. The vaccine strain was recovered from one heifer and her fetus at necropsy 1 week prior to estimated parturition. Data from this study suggests that SRB51 induces similar protective immunity across the recommended dosage range. The SRB51 vaccine may persist in some cattle into adulthood but the incidence and significance of this persistence remains unknown.

Quantitative assessment by flow cytometry of T-lymphocytes producing antigen-specific gamma-interferon in Brucella immune cattle

Peripheral blood mononuclear cells (PBMC) isolated from cattle infected with Brucella secreted gamma-interferon (IFN-gamma) after antigen-specific stimulation with Brucellergene, which is a mixture of cytoplasmic proteins of rough Brucella melitensis B115. Following the depletion of the monocyte-macrophages from the PBMC, the enriched lymphocyte populations stimulated with Brucellergene did not produce IFN-gamma. Two-colour immunofluorescence staining of intracellular IFN-gamma and bovine cell surface molecules identified the cells producing IFN-gamma among the PBMC stimulated with Brucellergene. Moreover, this method could be used to estimate the number of T-cells specifically producing IFN-gamma. For a given animal, there is a significant correlation (p < 0.05) between the production of IFN measured by an ELISA of the supernatant of whole blood stimulated with Brucellergene and the number of T-cells producing IFN-gamma after in vitro stimulation with Brucellergene. The development of the immunofluorescence staining technique provides a new tool for analysing and for measuring the T-cell immune response in cattle.

Protection against infection and abortion induced by virulent challenge exposure after oral vaccination of cattle with Brucella abortus strain RB51

OBJECTIVES

To determine efficacy of orally administered Brucella abortus vaccine strain RB51 against virulent B abortus challenge exposure in cattle as a model for vaccination of wild ungulates.

ANIMALS

20 mixed-breed beef cattle obtained from a brucellosis-free herd.

PROCEDURE

Sexually mature, Brucella-negative beef heifers were vaccinated by mixing > 10' viable RB51 organisms or diluent with their feed. Heifers were fed individually and consumed their entire ration. Each heifer received approximately 3 X 10' colony-forming units (CFU). Six weeks after oral vaccination, heifers were pasture-bred to brucellosis-free bulls. At approximately 186 days' gestation, heifers were challenge exposed conjunctively with 107 CFU of virulent B abortus strain 2308.

RESULTS

Vaccination with the rough variant of B abortus RB51 did not stimulate antibodies against the O-polysaccharide (OPS) of B abortus. After challenge exposure and parturition, strain 2308 was recovered from 80% of controls and only 20% of vaccinates. Only 30% of the vaccinates delivered dead, premature, or weak calves, whereas 70% of the controls had dead or weak calves.

CONCLUSIONS

Cattle vaccinated orally with the rough variant of B abortus strain RB51 develop significant (P < 0.05) protection against abortion and colonization and do not produce OPS-specific antibodies. Clinical Relevance-Results encourage further investigation into use of strain RB51 to vaccinate wild ungulates (elk and bison) orally.

Value of different serological tests in the diagnosis of bovine brucellosis in the Amazonian region

The high prevalence of brucellosis is one of the most serious animal health problems affecting cattle and buffalo herds of the Amazonian region. Modern diagnostic methods are not used or not even known, and thus test results are not available in that region. Therefore, in this study a total of 878 selected sera were subjected to comparative examination by five different serological tests (buffered plate agglutination test, tube agglutination test, complement fixation test, indirect ELISA, competitive ELISA). Indirect ELISA gave the highest number of positive results, except in samples derived from the Marajó island, for which the competitive ELISA proved to be the most sensitive. The sensitivity of the classical tests (agglutination, complement fixation) was markedly lower than that of the two ELISAs. After vaccination of 2-month-old heifer calves with the B19 vaccine, all tests showed a 50-60% seropositivity, which disappeared within four months.

Field study of vaccination of cattle with Brucella abortus strains RB51 and 19 under high and low disease prevalence

OBJECTIVE

To assess humoral and protective immunity in cattle vaccinated by 12 months with Brucella abortus vaccine strains RB51 and 19 under field conditions of high and low brucellosis prevalence.

ANIMALS

450 seronegative female cattle: 330 three to eight months old (calves), and 120 ten to twelve months old (heifers).

PROCEDURES

Ranch A had high prevalence (39%) of brucellosis, and ranch B had low prevalence (2%), as determined by results of conventional serologic testing: agar gel immunodiffusion and the ring test. Seronegative cattle were vaccinated once or twice with 5 x 10(9) colony-forming units of B abortus strain RB51 or once with strain 19. After vaccinating 285 cattle with strain RB51 and 165 with strain 19, 74 (26%) and 30 (18%), respectively, were bred to seropositive bulls, then were kept within the infected herd of origin.

RESULTS

All cattle vaccinated with strain 19 seroconverted 30 days later. All 285 cattle vaccinated with strain RB51 had negative results for all serologic tests, including agar gel immunodiffusion. All RB51-vaccinated cattle that became pregnant had negative results for the ring test and for conventional serologic tests after their first calving.

CONCLUSIONS

Strain RB51 can be used as a live organism vaccine without inducing antibody titers that interfere with serodiagnosis, and induced 100% protection against field strain B abortus-induced abortion in cattle vaccinated at least 1 year before mating to an infected bull. Vaccination with strain 19 under similar conditions was less effective than vaccination with strain RB51.

Serological cross-reactivity between Brucella abortus and yersinia enterocolitica 0:9: IV. Evaluation of the M- and C-epitope antibody response for the specific detection of B. abortus infections

Smooth lipopolysaccharides (SLPS) from Brucella abortus contain A-epitopes against which the majority of serum antibodies are directed during infections. SLPS from Yersinia enterocolitica 0:9 possesses identical epitopes, which are the cause for serological cross-reactivity. All Brucella spp. possess M- and C-epitopes which are not present in Y. enterocolitica 0:9. In order to examine the usefulness of these M- and C-epitopes for discriminatory serological testing, a panel of sera were used in this study, comprising sera from Y. enterocolitica 0:9-infected heifers, sera from B. abortus-infected cattle of comparable strength in the serological brucellosis tests to the sera from Y. enterocolitica 0:9-infected heifers, sera from B. abortus-infected bovines with strong serological reactions and sera from animals free from B. abortus or Y. enterocolitica infections. These sera were tested in blocking ELISAs with seven M- and one C-epitope-specific monoclonal antibodies in combination with SLPS from B. melitensis M16 high in M-epitopes as antigen. Strong B. abortus sera inhibited most strongly, while negative sera showed no or little inhibition. Sera with weak or intermediate titres blocked to a lower extent. Unexpectedly, the sera from Y. enterocolitica 0:9-infected heifers showed inhibition behaviour virtually identical to the comparable sera from B. abortus infected animals. Absorbing out of the A-epitope specific serum antibodies with either Y. enterocolitica 0:9 SLPS or with Y. enterocolitica 0:9 bacteria, indicated the presence of M- or C-epitope-specific serum antibodies in some sera from B. abortus-infected cattle but not in the sera from Y. enterocolitica 0:9-infected animals. These results demonstrate that the M- or C-epitope-specific antibody response in sera from B. abortus infected cattle is only of limited value for the serological discrimination between B. abortus and Y. enterocolitica 0:9 infections.