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

Authors: Olsen, Steven; Boggiatto, Paola; KANIPE, CARLY - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2020
Publication Date: 9/1/2020
Citation: Olsen, S.C., Boggiatto, P.M., Kanipe, C. 2020. Immune responses and clinical effects of experimental challenge of elk with Brucella abortus strain 2308. Veterinary Immunology and Immunopathology. 227. https://doi.org/10.1016/j.vetimm.2020.110086.
DOI: https://doi.org/10.1016/j.vetimm.2020.110086

Interpretive Summary: Elk are a natural reservoir for brucellosis in the in Yellowstone National Park and surrounding areas. Brucellosis causes reproductive losses in domestic livestock and can also cause clinical disease in humans. In this study we evaluated the incidence of infection and abortion in non-vaccinated elk after experimental challenge with a virulent Brucella abortus strain during early or late pregnancy. We found that elk have fewer abortions as compared to other large animal reservoir hosts although infection rates are similar. Infected animals earlier in pregnancy or with a higher dose of the virulent strain did not influence abortion or infection rates. Development of a repeatable challenge model in elk that induces significant abortion rates is critical for evaluation of the efficacy of proposed vaccines. This data will be of interest to scientists studying brucellosis, regulatory personnel, and people with responsibilities for managing free-ranging elk populations.

Technical Abstract: To assess the effects of challenge dose and stage of gestation on infection and abortion, 35 elk were conjunctivally challenged with virulent Brucella abortus strain 2308 (S2308) during pregnancy. Seventeen elk were experimentally challenged early in gestation (December) with high (approximately 108 CFU) or low challenge (approximately 107 CFU) treatments having 8 and 9 pregnant elk, respectively. Other pregnant elk were experimentally challenged at a later challenge time (approximately early third trimester, February), with high and low challenge treatments having 8 and 10 elk, respectively. Conjunctival swabs from all animals were culture positive for the S2308 strain at 7 days after experimental challenge. All animals seroconverted on a B. abortus ELISA but optical density readings were not influenced (P>0.05) by time of challenge or by challenge dosage. In the early challenge group, abortions occurred in 2 of 9 (22%) in the low challenge treatment and 3 of 8 (37%) in the high challenge treatment, whereas in the later challenge group, 1 of 8 (12.5%) in the low challenge treatment and 2 of 10 (20%) in the high challenge treatment aborted. The ability to recover B. abortus from samples obtained at necropsy did not differ (P>0.05) between early and late challenges or between high and low challenge treatments. Despite the lack of abortions observed after experimental challenge, recovery from maternal tissues ranged from 50% (low dose, late challenge) to 77% (low dose, early challenge). Our data suggests that naïve elk do not abort as frequently after experimental infection with B. abortus strain 2308 as compared to similar data in cattle and bison.