Submitted to: Journal of Wildlife Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2008
Publication Date: 1/1/2009
Citation: Nol, P., Olsen, S.C., Rhyan, J.C. 2009. Experimental Infection of Richardson's Ground Squirrels (Spermophilus richardsonii) with Attenuated and Virulent Strains of Brucella abortus. Journal of Wildlife Diseases. 45(1):189-195. Interpretive Summary: Brucella abortus is a disease that causes abortion and associated economic losses in infected cattle herds. The prevalence of B. abortus within bison and elk in Yellowstone National Park pose a risk to the completion of the Brucellosis Eradication Program for cattle. A safe and protective vaccine for wildlife within Yellowstone National Park is needed. Any proposed vaccine would need to be demonstrated to be safe in the environment including other nontarget animals. In this study, we evaluated a brucellosis vaccine and characterized its safety in a nontarget species (Richardson ground squirrels). Our data suggest this vaccine did not induce illness or mortality if ground squirrels were orally infected. This data will be of benefit to the National Park Service and the states of Montana, Wyoming, and Idaho in their efforts to resolve the brucellosis problem in the Yellowstone National Park and surrounding areas. Identification of a safe and protective brucellosis vaccine for wildlife will help prevent transmission of brucellosis to cattle herds and assist in the completion of the Brucellosis Eradication Program.
Technical Abstract: Exposure of non-target species to wildlife vaccines is an important concern when evaluating a candidate vaccine for use in the field. A previous investigation of the safety of Brucella abortus strain RB51 (sRB51) in various non-target species suggested that Richardson’s ground squirrels (Spermophilus richardsonii) may develop persistent infections when orally inoculated with the vaccine. In this study sRB51, B. abortus strain 19 (s19), and virulent B. abortus strain 9-941 (s9941) were administered orally to Richardson’s ground squirrels to further evaluate this species’ susceptibility to B. abortus infection. Six groups of non-gravid ground squirrels were orally inoculated with 6 x 10**8 cfu sRB51 (n=10), 2.5 x 10**4 cfu s19 (n=10), 2.5 x 10**7 cfu s19 (n=7), 1.3 x 10**6 cfu s s9941 (n=5), 2.1 x 10**8 cfu s9941 (n=5), or vaccine diluent (control) (n=4). Although 2 animals in the higher dose s19 group and 1 animal in each of the other inoculated groups showed persistence of bacteria in various tissues 14 to 18 weeks post inoculation, we found no evidence of pathology caused by B. abortus in non-pregnant Richardson’s ground squirrels based on clinical signs, gross lesions, and histopathology.