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

Abstract

The Brucella abortus vaccine strain RB51 (SRB51) is being considered for use in the management of brucellosis in wild bison ( Bison bison ) and elk ( Cervus elaphus ) populations in the Greater Yellowstone Area (USA). Evaluation of the vaccine's 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 the 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 morbibity or mortality in ravens, ground squirrels, deer mice, or prairie voles.