Immune responses and clinical effects of experimental challenge of elk with Brucella abortus strain 2308

Fecal and vaginal microbiota of vaccinated and non-vaccinated pregnant elk challenged with Brucella abortus

Introduction

Brucella abortus is the causative agent of brucellosis in cattle and in humans, resulting in economic losses in the agricultural sector and representing a major threat to public health. Elk populations in the American Northwest are reservoirs for this bacterium and transmit the agent to domestic cattle herds. One potential strategy to mitigate the transmission of brucellosis by elk is vaccination of elk populations against B. abortus; however, elk appear to be immunologically distinct from cattle in their responses to current vaccination strategies. The differences in host response to B. abortus between cattle and elk could be attributed to differences between the cattle and elk innate and adaptive immune responses. Because species-specific interactions between the host microbiome and the immune system are also known to affect immunity, we sought to investigate interactions between the elk microbiome and B. abortus infection and vaccination.

Methods

We analyzed the fecal and vaginal microbial communities of B. abortus-vaccinated and unvaccinated elk which were challenged with B. abortus during the periparturient period.

Results

We observed that the elk fecal and vaginal microbiota are similar to those of other ruminants, and these microbial communities were affected both by time of sampling and by vaccination status. Notably, we observed that taxa representing ruminant reproductive tract pathogens tended to increase in abundance in the elk vaginal microbiome following parturition. Furthermore, many of these taxa differed significantly in abundance depending on vaccination status, indicating that vaccination against B. abortus affects the elk vaginal microbiota with potential implications for animal reproductive health.

Discussion

This study is the first to analyze the vaginal microbiota of any species of the genus Cervus and is also the first to assess the effects of B. abortus vaccination and challenge on the vaginal microbiome.

Immune Responses and Efficacy of Brucella Abortus Strain RB51 in Bison After Delivery in a Dry Dart Formulation or by Parenteral Inoculation

Bison (Bison bison) heifer calves (n = 32) were randomly assigned to control or vaccination with 10¹⁰ colony-forming units of Brucella abortus strain RB51 (RB51) vaccine by single or boostered parenteral delivery, or by surgical implantation of a dry dart formulation (n = 8/trt). Serum and/or peripheral blood mononuclear cells (PBMC) were obtained at 0, 4, 8, 13, 16, 21, and 24 wks after initial vaccination and at 0, 4, 8, 12, 15, 22, and 27 wks after booster vaccination to characterize humoral and cellular immune responses to RB51. Bison in both RB51 vaccination treatments demonstrated greater (P < 0.0001) serum humoral responses when compared to non-vaccinates, with parenteral vaccinates demonstrating greater (P < 0.01) responses when compared to mean responses of bison inoculated with the dry dart. Only the booster vaccinated treatment demonstrated greater (P < 0.0001) humoral responses than control bison in samples collected after re-inoculation. At 4, 8, 12, 16, and 24 wks after initial vaccination, PBMC from parenteral RB51 vaccinates demonstrated greater proliferative responses to RB51 when compared to responses of control animals. In comparison, bison inoculated with the RB51 dry dart did not demonstrate greater (P > 0.05) proliferative responses when compared to responses of non-vaccinates. Bison were pasture bred and pregnant animals experimentally challenged in mid-gestation with 10⁷ CFU of B. abortus strain 2,308. Bison in parenteral vaccination treatments had reduced (P < 0.05) abortions and infection in uterine and fetal samples as compared to non-vaccinated bison, with booster vaccinates tending to have the lowest colonization (CFU/gm) in tissues. In comparison, the dry dart formulation did reduce abortion (P < 0.05) but not infection (P > 0.05) in most tissues when compared to non-vaccinated bison. The results of this study reaffirm the efficacy of boostered parenteral vaccination of bison with RB51 in preventing brucellosis. Our data also suggests that the novel dry dart RB51 formulation does not induce sufficient efficacy in bison after a single inoculation.