Abortus Vaccine Strain Research Articles

Expression and Validation of D-Erythrulose 1-Phosphate Dehydrogenase from Brucella abortus: A Diagnostic Reagent for Bovine Brucellosis

Brucella abortus is a bacterium of brucellosis causing abortion in cattle. The diagnosis of bovine brucellosis mainly relies on serologic tests using smooth lipopolysaccharide (S-LPS) from B. abortus. However, the usefulness of this method is limited by false-positive reactions due to cross-reaction with other Gram-negative bacteria. In the present study, the eryC gene encoding B. abortus d-erythrulose 1-phosphate dehydrogenase, which is involved in the erythritol metabolism in virulent B. abortus strain but is absent from a B. abortus vaccine strain (S19), was cloned. Recombinant EryC was expressed and purified for the evaluation as a diagnostic reagent for bovine brucellosis. Other B. abortus proteins, Omp16, PP26, and CP39 were also purified and their seroreactivities were compared. Recombinant EryC, Omp16, PP26, and PP39 were all reactive to B. abortus-positive serum. The specificity of recombinant Omp16, PP26, CP39, and EryC, were shown to be approximately 98%, whereas that of B. abortus whole cell lysates was shown to be 95%. The sensitivity of Omp16, PP26, CP39, and EryC were 10%, 51%, 64%, and 43%, respectively, whereas that of B. abortus whole cell lysates was 53%. These results suggested that B. abortus EryC would be a potential reagent for diagnosis for bovine brucellosis as a single protein antigen.

Evidence of Chlamydophila abortus vaccine strain 1B as a possible cause of ovine enzootic abortion

Chlamydophila abortus, the agent of ovine enzootic abortion (OEA), is a major cause of lamb mortality worldwide. Disease can be controlled through the use of vaccines based on the 1B temperature-sensitive mutant strain of C. abortus. This study investigated suspected OEA cases across Scotland for the presence of the 1B strain by analysis of recently identified unique point mutations (9). Thirty-five cases were C. abortus-positive and 14 came from vaccinated flocks. Analysis of single nucleotide polymorphisms by PCR-RFLP and sequence analysis revealed the presence of point mutations consistent with the presence of the 1B vaccine strain in 5 of these 14 samples. Quantitative real-time PCR revealed comparable numbers of genome copies of the 1B strain in infected placentas to those present following wild-type infection. This study is the first to demonstrate the presence of the 1B vaccine strain in the placentas of OEA cases and suggests a probable causal role in the disease.

The significance of TLRs in Brucella mediated dendritic cell activation in vitro and pulmonary clearance in vivo (42.16)

Abstract Brucellosis is a worldwide zoonoses affecting 500,000 people annually with no approved human vaccines available. Live attenuated B. abortus vaccine strain RB51 protects cattle through CD4 and CD8 T-cell mediated responses. However, there are concerns regarding its efficacy and use as a live vaccine in people. Therefore, identifying how Brucella vaccines stimulate innate and adaptive immunity is critical to enhancing vaccine efficacy. Brucella stimulate dendritic cells (DCs) through Toll-Like Receptors (TLRs) 2, 4 and 9. In this study, to identify how rough vaccine strains stimulate DC activation and function in vitro, we used vaccine strain RB51 versus pathogenic strain 2308 to stimulate bone marrow derived dendritic cells (BMDCs) from TLR2, 4 or 9 knockout (KO) and wild type BALB/c mice. Since inhalation of infected aerosols is one of the most common routes of exposure, in vivo clearance of strain RB51 compared to strain 2308 from intranasally (IN) infected TLR KO vs. control BALB/c mice was assessed. We determined that strain RB51 induced significant (p≤0.05) DC activation compared to strain 2308 which was TLR independent. However, strain RB51 induced TNF - α production was TLR2 and TLR9 dependent and IL-12 production was TLR2 and TLR4 dependent. TLR4 KO mice had significantly (p≤0.05) delayed pulmonary clearance of strain RB51 in vivo at day 14 post infection. Based on these data, future studies will focus on enhancing the protective ability of strain RB51.

Caspase-2 Mediated Apoptotic and Necrotic Murine Macrophage Cell Death Induced by Rough Brucella abortus

Brucella species are Gram-negative, facultative intracellular bacteria that cause zoonotic brucellosis. Survival and replication inside macrophages is critical for establishment of chronic Brucella infection. Virulent smooth B. abortus strain 2308 inhibits programmed macrophage cell death and replicates inside macrophages. Cattle B. abortus vaccine strain RB51 is an attenuated rough, lipopolysaccharide O antigen-deficient mutant derived from smooth strain 2308. B. abortus rough mutant RA1 contains a single wboA gene mutation in strain 2308. Our studies demonstrated that live RB51 and RA1, but not strain 2308 or heat-killed Brucella, induced both apoptotic and necrotic cell death in murine RAW264.7 macrophages and bone marrow derived macrophages. The same phenomenon was also observed in primary mouse peritoneal macrophages from mice immunized intraperitoneally with vaccine strain RB51 using the same dose as regularly performed in protection studies. Programmed macrophage cell death induced by RB51 and RA1 was inhibited by a caspase-2 inhibitor (Z-VDVAD-FMK). Caspase-2 enzyme activation and cleavage were observed at the early infection stage in macrophages infected with RB51 and RA1 but not strain 2308. The inhibition of macrophage cell death promoted the survival of rough Brucella cells inside macrophages. The critical role of caspase-2 in mediating rough B. abortus induced macrophage cell death was confirmed using caspase-2 specific shRNA. The mitochondrial apoptosis pathway was activated in macrophages infected with rough B. abortus as demonstrated by increase in mitochondrial membrane permeability and the release of cytochrome c to cytoplasm in macrophages infected with rough Brucella. These results demonstrate that rough B. abortus strains RB51 and RA1 induce apoptotic and necrotic murine macrophage cell death that is mediated by caspase-2. The biological relevance of Brucella O antigen and caspase-2-mediated macrophage cell death in Brucella pathogenesis and protective Brucella immunity is discussed.

Genome Sequence of Brucella abortus Vaccine Strain S19 Compared to Virulent Strains Yields Candidate Virulence Genes

The Brucella abortus strain S19, a spontaneously attenuated strain, has been used as a vaccine strain in vaccination of cattle against brucellosis for six decades. Despite many studies, the physiological and molecular mechanisms causing the attenuation are not known. We have applied pyrosequencing technology together with conventional sequencing to rapidly and comprehensively determine the complete genome sequence of the attenuated Brucella abortus vaccine strain S19. The main goal of this study is to identify candidate virulence genes by systematic comparative analysis of the attenuated strain with the published genome sequences of two virulent and closely related strains of B. abortus, 9–941 and 2308. The two S19 chromosomes are 2,122,487 and 1,161,449 bp in length. A total of 3062 genes were identified and annotated. Pairwise and reciprocal genome comparisons resulted in a total of 263 genes that were non-identical between the S19 genome and any of the two virulent strains. Amongst these, 45 genes were consistently different between the attenuated strain and the two virulent strains but were identical amongst the virulent strains, which included only two of the 236 genes that have been implicated as virulence factors in literature. The functional analyses of the differences have revealed a total of 24 genes that may be associated with the loss of virulence in S19. Of particular relevance are four genes with more than 60bp consistent difference in S19 compared to both the virulent strains, which, in the virulent strains, encode an outer membrane protein and three proteins involved in erythritol uptake or metabolism.

Reduced cerebral infection of Neospora caninum in BALB/c mice vaccinated with recombinant Brucella abortus RB51 strains expressing N. caninum SRS2 and GRA7 proteins

Neospora caninum, an obligate intracellular protozoan parasite, is the causative agent of bovine neosporosis, an important disease affecting the reproductive performance of cattle worldwide. Currently there is no effective vaccine available to prevent N. caninum infection in cattle. In this study, we examined the feasibility of developing a live, recombinant N. caninum vaccine using Brucella abortus vaccine strain RB51 as the expression and delivery vector. We generated two recombinant RB51 strains each expressing SRS2 (RB51/SRS2) or GRA7 (RB51/GRA7) antigens of N. caninum. BALB/c mice immunized by single intraperitoneal inoculation of the recombinant RB51 strains developed IgG antibodies specific to the respective N. caninum antigen. In vitro stimulation of splenocytes from the vaccinated mice with specific antigen resulted in the production of interferon-γ, but not IL-5 or IL-10, suggesting the development of a Th1 type immune response. Upon challenge with N. caninum tachyzoites, mice vaccinated with strain RB51/SRS2, but not RB51/GRA7, showed significant resistance to cerebral infection when compared to the RB51 vaccinated mice, as determined by the tissue parasite load using a real-time quantitative TaqMan assay. Interestingly, mice vaccinated with either strain RB51 or RB51/GRA7 also contained significantly lower parasite burden in their brains compared to those inoculated with saline. Mice vaccinated with strain RB51/SRS2 or RB51/GRA7 were protected to the same extent as the strain RB51 vaccinated mice against challenge with B. abortus virulent strain 2308. These results suggest that a recombinant RB51 strain expressing an appropriate protective antigen(s), such as SRS2 of N. caninum, can confer protection against both neosporosis and brucellosis.

EFFICACY OF SINGLE CALFHOOD VACCINATION OF ELK WITH BRUCELLA ABORTUS STRAIN 19

Brucellosis has been eradicated from cattle in the states of Wyoming, Montana, and Idaho, USA. However, free-ranging elk (Cervus elaphus) that use feedgrounds in the Greater Yellowstone Area (GYA) and bison (Bison bison) in Yellowstone and Grand Teton national parks still have high seroprevalence to the disease and have caused loss of brucellosis-free status in Wyoming. Management tools to control or eliminate the disease are limited; however, wildlife vaccination is among the methods currently used by wildlife managers in Wyoming. We conducted a controlled challenge study of single calfhood vaccination. Elk calves, caught in January and February of 1999 and 2000 and acclimated to captivity for 3 weeks, were randomly assigned to control or vaccinate groups. The vaccinate groups received Brucella abortus vaccine strain 19 (S19) by hand-delivered intramuscular injection. Calves were raised to adulthood and bred at either 2.5 or 3.5 years of age for 2000 and 1999 captures, respectively. Eighty-nine (44 controls, 45 vaccinates) pregnant elk entered the challenge portion of the study. We challenged elk at mid-gestation with pathogenic B. abortus strain 2308 by intraconjunctival instillation. Abortion occurred in significantly more (P = 0.002) controls (42; 93%) than vaccinates (32; 71%), and vaccine protected 25% of the vaccinate group. We used Brucella culture of fetus/calf tissues to determine the efficacy of vaccination for preventing infection, and we found that the number of infected fetuses/calves did not differ between controls and vaccinates (P = 0.14). Based on these data, single calfhood vaccination with S19 has low efficacy, will likely have only little to moderate effect on Brucella prevalence in elk, and is unlikely to eradicate the disease in wildlife of the GYA.

Efficacy of live Chlamydophila abortus vaccine 1B in protecting mice placentas and foetuses against strains of Chlamydophila pecorum isolated from cases of abortion

The efficacy of Chlamydophila abortus vaccine strain 1B in protecting against two selected Chlamydophila pecorum strains, isolated from an aborted goat (M14) in Morocco and a ewe (AB10) in France, was investigated in a mouse model, by comparing the reduction in number of bacteria in the placentas of vaccinated mice challenged intraperitoneally at 11 days of pregnancy with the reference C. abortus (AB7) and C. pecorum (M14, or AB10) strains, to those of unvaccinated mice. Vaccine 1B was shown to provide effective protection against the field strains of C. pecorum, since it significantly reduced the placental Chlamydophila colonisation. The two C. pecorum strains were not sufficiently abortifacient in mice to use reduction in abortion as a criterion of protection.

A DNA vaccine encoding Cu,Zn superoxide dismutase of Brucella abortus induces protective immunity in BALB/c mice.

This study was conducted to evaluate the immunogenicity and protective efficacy of a DNA vaccine encoding Brucella abortus Cu,Zn superoxide dismutase (SOD). Intramuscular injection of plasmid DNA carrying the SOD gene (pcDNA-SOD) into BALB/c mice elicited both humoral and cellular immune responses. Animals injected with pcDNA-SOD developed SOD-specific antibodies which exhibited a dominance of immunoglobulin G2a (IgG2a) over IgG1. In addition, the DNA vaccine elicited a T-cell-proliferative response and also induced the production of gamma interferon, but not interleukin-10 (IL-10) or IL-4, upon restimulation with either recombinant SOD or crude Brucella protein, suggesting the induction of a typical T-helper-1-dominated immune response in mice. The pcDNA-SOD (but not the control vector) induced a strong, significant level of protection in BALB/c mice against challenge with B. abortus virulent strain 2308; the level of protection was similar to the one induced by B. abortus vaccine strain RB51. Altogether, these data suggest that pcDNA-SOD is a good candidate for use in future studies of vaccination against brucellosis.

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.

Use of Detergent Extracts ofBrucella AbortusRB51 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.

Oral vaccination of sexually mature pigs with Brucella abortus vaccine strain RB51.

To develop a novel oral vaccine delivery system for swine, using the rough vaccine strain of Brucella abortus. 56 crossbred pigs from a brucellosis-free facility. In 3 separate experiments, pigs were orally vaccinated with doses of 1 x 10(9) to > 1 x 10(11) CFU of strain RB51 vaccine. The vaccine was placed directly on the normal corn ration, placed inside a whole pecan, or mixed with cracked pecans and corn. Oral vaccination of pigs with vaccine strain RB51 resulted in a humoral immune response to strain RB51 and short-term colonization of the regional lymph nodes. A viscous liquid such as Karo corn syrup in association with pecans that scarify the oral mucosa are necessary when placing the live vaccine directly onto corn or other food rations. Doses of > 1 x 10(11) CFU of RB51 organisms/pig in this mixture ensures 100% colonization of regional lymph nodes via the oral route. This method may allow an efficient and economical means to vaccinate feral swine for brucellosis.

Experimental infection of nontarget species of rodents and birds with Brucella abortus strain RB51 vaccine.

The Brucella abortus vaccine strain RB51 (SRB51) is being considered for use in the management of bnucellosis in wild bison (Bison bison) and elk (Cervus elaphus) populations in the Greater Yellowstone Area (USA). Evaluation of the vaccines safety in non-target species was considered necessary prior to field use. Between June 1998 and December 1999, ground squirrels (Spermophilus richardsonii, n = 21), deer mice (Peromyscus maniculatus, n = 14), prairie voles (Microtus ochrogaster, n = 21), and ravens (Corvus corax, n = 13) were orally inoculated with SRB51 or physiologic saline. Oral and rectal swabs and blood samples were collected for bacteriologic evaluation. Rodents were necropsied at 8 to 10 wk and 12 to 21 wk post inoculation (PI), and ravens at 7 and 11 wk PI. Spleen, liver and reproductive tissues were collected for bacteriologic and histopathologic evaluation. No differences in clinical signs, appetite, weight loss or gain, or activity were observed between saline- and SRB51-inoculated animals in all four species. Oral and rectal swabs from all species were negative throughout the study. In tissues obtained from SRB51-inoculated animals, the organism was isolated from six of seven (86%) ground squirrels, one of six (17%) deer mice, none of seven voles, and one of five (20%) ravens necropsied at 8, 8, 10, and 7 wk PI, respectively. Tissues from four of seven (57%) SRB51-inoculated ground squirrels were culture positive for the organism 12 wk PI; SRB51 was not recovered from deer mice, voles. or ravens necropsied 12, 21, or 11 wk, respectively, PI. SRB51 was not recovered from saline-inoculated ground squirrels, deer mice, or voles at any time but was recovered from one saline-inoculated raven at necropsy, 7 wk PI, likely attributable to contact with SRB51-inoculated ravens in an adjacent aviary room. Spleen was time primary tissue site of colonization in ground squirrels, followed by the liver and reproductive organs. The results indicate oral exposure to SRB51 does not produce morbidity or mortality in ravens, ground squirrels, deer mice, or prairie voles.

Deletion of wboA enhances activation of the lectin pathway of complement in Brucella abortus and Brucella melitensis.

Brucella spp. are gram-negative intracellular pathogens that survive and multiply within phagocytic cells of their hosts. Smooth organisms present O polysaccharides (OPS) on their surface. These OPS help the bacteria avoid the bactericidal action of serum. The wboA gene, coding for the enzyme glycosyltransferase, is essential for the synthesis of O chain in Brucella. In this study, the sensitivity to serum of smooth, virulent Brucella melitensis 16M and B. abortus 2308, rough wboA mutants VTRM1, RA1, and WRR51 derived from these two Brucella species, and the B. abortus vaccine strain RB51 was assayed using normal nonimmune human serum (NHS). The deposition of complement components and mannose-binding lectin (MBL) on the bacterial surface was detected by flow cytometry. Rough B. abortus mutants were more sensitive to the bactericidal action of NHS than were rough B. melitensis mutants. Complement components were deposited on smooth strains at a slower rate compared to rough strains. Deposition of iC3b and C5b-9 and bacterial killing occurred when bacteria were treated with C1q-depleted, but not with C2-depleted serum or NHS in the presence of Mg-EGTA. These results indicate that (i) OPS-deficient strains derived from B. melitensis 16M are more resistant to the bactericidal action of NHS than OPS-deficient strains derived from B. abortus 2308, (ii) both the classical and the MBL-mediated pathways are involved in complement deposition and complement-mediated killing of Brucella, and (iii) the alternative pathway is not activated by smooth or rough brucellae.

Identification of an IS711 element interrupting the wboA gene of Brucella abortus vaccine strain RB51 and a PCR assay to distinguish strain RB51 from other Brucella species and strains.

Brucella abortus vaccine strain RB51 is a natural stable attenuated rough mutant derived from the virulent strain 2308. The genetic mutations that are responsible for the roughness and the attenuation of strain RB51 have not been identified until now. Also, except for an assay based on pulsed-field gel electrophoresis, no other simple method to differentiate strain RB51 from its parent strain 2308 is available. In the present study, we demonstrate that the wboA gene encoding a glycosyltransferase, an enzyme essential for the synthesis of O antigen, is disrupted by an IS711 element in B. abortus vaccine strain RB51. Exploiting this feature, we developed a PCR assay that distinguishes strain RB51 from all other Brucella species and strains tested.

Genetic characterization of a Tn5-disrupted glycosyltransferase gene homolog in Brucella abortus and its effect on lipopolysaccharide composition and virulence.

We constructed a rough mutant of Brucella abortus 2308 by transposon (Tn5) mutagenesis. Neither whole cells nor extracted lipopolysaccharide (LPS) from this mutant, designated RA1, reacted with a Brucella O-side-chain-specific monoclonal antibody (MAb), Bru-38, indicating the absence of O-side-chain synthesis. Compositional analyses of LPS from strain RA1 showed reduced levels of quinovosamine and mannose relative to the levels in the parental, wild-type strain, 2308. We isolated DNA flanking the Tn5 insertion in strain RA1 by cloning a 25-kb XbaI genomic fragment into pGEM-3Z to create plasmid pJM6. Allelic exchange of genomic DNA in B. abortus 2308 mediated by electroporation of pJM6 produced kanamycin-resistant clones that were not reactive with MAb Bru-38. Southern blot analysis of genomic DNA from these rough clones revealed Tn5 in a 25-kb XbaI genomic fragment. A homology search with the deduced amino acid sequence of the open reading frame disrupted by Tn5 revealed limited homology with various glycosyltransferases. This B. abortus gene has been named wboA. Transformation of strain RA1 with a broad-host-range plasmid bearing the wild-type B. abortus wboA gene resulted in the restoration of O-side-chain synthesis and the smooth phenotype. B. abortus RA1 was attenuated for survival in mice. However, strain RA1 persisted in mice spleens for a longer time than the B. abortus vaccine strain RB51, but as expected, neither strain induced antibodies specific for the O side chain.

Modulation of Endocytosis in Nuclear Factor IL-6(−/−) Macrophages Is Responsible for a High Susceptibility to Intracellular Bacterial Infection

Activated macrophages kill bacteria, a function known to depend on the expression of NF-IL-6. Here, it is demonstrated that the attenuated Brucella abortus vaccine strain 19 replicates much better in NF-IL-6-/- than in NF-IL-6(+/+) and NF-IL-6(+/+)-activated murine macrophages and at levels comparable to those observed in normal macrophages infected with the pathogenic strain 2308. The role of NF-IL-6 in the inhibition of intracellular bacterial replication is related to its control of endocytosis and membrane fusion between endosomes and Brucella-containing phagosomes. Addition of the granulocyte-CSF (G-CSF), whose induction is impaired in NF-IL-6(-/-) macrophages, restores both endocytosis and the morphology of endosomes, together with bactericidal activity. Regulation of membrane traffic in endocytosis by G-CSF whose expression is controlled by NF-IL-6 may explain how a host cell can control intracellular bacterial replication.

Vaccination with live Escherichia coli expressing Brucella abortus Cu/Zn superoxide dismutase protects mice against virulent B. abortus.

Vaccination of mice with Escherichia coli expressing Brucella Cu/Zn superoxide dismutase (SOD) [E. coli(pBSSOD)] induced a significant level of protection against virulent Brucella abortus challenge, although this level was not as high as the one reached with B. abortus vaccine strain RB51. In addition, vaccination with E. coli(pBSSOD) induced antibodies to Cu/Zn SOD and a strong proliferative response of splenocytes when stimulated in vitro with a thioredoxin-Cu/Zn SOD fusion protein.

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

Abstract 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 &gt; 1010 viable RB51 organisms or diluent with their feed. Heifers were fed individually and consumed their entire ration. Each heifer received approximately 3×1010 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&lt; 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. (Am J Vet Res1998; 59:1575-1578)Vol 59, No. 12, December 1998

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

Abstract 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 × 109 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. (Am J Vet Res 1998;59:1016–1020)