Protection of Cattle against Epizootic Bovine Abortion (EBA) Using a Live Pajaroellobacter abortibovis Vaccine.

Epizootic bovine abortion (EBA) is an arthropod-borne bacterial disease that causes significant economic loss for cattle producers in the western United States. The etiologic agent, Pajaroellobacter abortibovis, is an intracellular pathogen that has yet to be cultivated in vitro, thereby requiring novel methodologies for vaccine development. A vaccine candidate, using live P. abortibovis-infected cells (P.a-LIC) harvested from mouse spleens, was tested in beef cattle. Over the course of two safety studies and four efficacy trials, safety risks were evaluated, and dosage and potencies refined. No incidence of anaphylaxis, recognized health issues or significant impact upon conception rates were noted. Vaccination did result in subclinical skin reactions. Early fetal losses were noted in two trials and were significant when the vaccine was administered within 21 days prior to conception. Administration of the EBA agent (EBAA) vaccine as a single dose, at a potency of 500 P.a-LIC, 56 days prior to breeding, provided 100% protection with no early fetal losses. Seroconversion occurred in all animals following EBAA vaccination and corresponded well with protection of the fetus from epizootic bovine abortion.

Assessment of a fluorescent antibody test for the detection of antibodies against epizootic bovine abortion.

The current study was directed at developing and validating an indirect fluorescent antibody test (IFAT) capable of detecting antibodies specific for the agent of epizootic bovine abortion (aoEBA). Sensitivity and specificity was determined by comparing antibody titers from 114 fetuses infected with aoEBA with 68 fetuses diagnosed with alternate infectious etiologies. Data established specificity at 100% and sensitivity at 94.7% when cutoff criteria for a positive test were assigned at a titer of ≥1,000. Potential cross-reactivity was noted in samples from 3 fetuses with antibody titers of 10 or100; all were infected with Gram-positive organisms. The remaining 65 fetuses infected with microbes other than aoEBA, and an additional 12 negative reference sera, did not have detectable titers. The IFAT-based serology assay is rapid, reproducible, and unaffected by fluid color or opacity. Total fetal immunoglobulin (Ig)G was also evaluated as an aid for diagnosing EBA. Significantly higher concentrations of IgG were identified in fetuses infected with aoEBA as compared to those with alternate infectious etiologies. The presence of IgG is a sensitive indicator of EBA and increases the specificity of FAT-based serologic diagnosis when titers are 10 or 100. Taken together, serology and IgG analyses suggest that the incidence of EBA may be underestimated.

Differential levels of mRNA transcripts encoding immunologic mediators in mammary gland secretions from dairy cows with subclinical environmental Streptococci infections.

Dry-off, and the period around parturition, are associated with increased susceptibility to intramammary infections in dairy cows. The immunological profiles of mammary gland secretions during these periods are not well described. The objective of the present study was to better characterize association(s) between chronic subclinical Environmental Streptococci infections at dry-off and relative levels of mRNA transcripts encoding multiple immunologic mediators present in cells derived from mammary gland secretions at dry-off and continuing through parturition. The chronic subclinical bacterial infections in the present study were characterized by multiple isolations of Streptococcus species and elevated SSC for a minimum of three weeks prior to dry-off. The majority of differences between principal and control quarters were identified at dry-off. Transcript levels of IL-17, IL2Rα and iNOS were increased while pro-inflammatory cytokine IL-6, and the regulatory cytokine IL-10, were reduced. Following antibiotic treatment of mammary glands, IL-17 transcripts remained elevated over the course of the study, indicative of a persistent insult. IL-4 transcript levels were modestly elevated at 7 days following dry-off and significantly elevated at 14 days, consistent with activated T(H)1 and T(H)2 lymphocytes in the principal quarters, respectively. From a temporal perspective, transcript levels of IL-8 decreased in all animals through the dry-off period animals and returned to pre-dry-off levels at parturition; levels of iNOS peaked at parturition. Five of the six principal cows experienced recurrent bacterial mastitis during the subsequent lactation; four were in the same quarter as was initially infected with Streptococcus and three of these four were due to coliforms. Taken together, this apparent chronic susceptibility of select mammary glands to bacterial infection would suggest a physiologic and/or immunologic dysfunction. Identification of factor(s) that contribute to the predisposition of mammary glands to developing mastitis should facilitate development of new control strategies.