Abstract
Brucellosis in Greater Yellowstone Area (GYA) bison and elk has been a source of controversy and wildlife management for many years. Research on brucellosis has been conducted in numerous facilities that house captive wildlife to generate data on the disease in elk, bison, and reindeer.
From 1999 to 2002, approximately 100 elk were held captive at the Idaho Department of Fish and Game Wildlife Health Laboratory in Caldwell, Idaho to evaluate the efficacy of single-dose, calfhood vaccination using Brucella abortus strain 19 (S19). These elk were challenged with 1 × 107 CFU of pathogenic Brucella abortus strain 2308 (S2308) by bilateral intraconjunctival sac instillation on February 28, 2002. Abortions occurred between March and June 2002, and live births occurred in May and June 2002. All elk in the vaccine study were euthanatized by late June 2002.
All resident animals at the Wildlife Health Laboratory undergo annual health checks including serologic testing for brucellosis. None have been found to be seropositive to brucellosis until summer and fall of 2002. In July 2002, a 2-year-old bull bison was found to be serologically positive to brucellosis at slaughter. On follow-up testing, two additional bison cows were found to be seropositive. In August 2002, three adult bull elk were found to be seropositive to brucellosis. One bull was culture positive for S2308 on a semen sample collected in December 2002 and again at slaughter in February 2003. In late summer and fall 2002, three adult elk cows were found to be seropositive to brucellosis. In addition, a group of six seronegative adult female elk were joined with a seropositive bull elk in fall of 2002. To date, three of these elk have seroconverted.
An extensive epidemiologic investigation was undertaken to try to determine the source and strain of the brucellosis that appears to have crossed at least two fence lines uphill from the elk challenged with S19. No common use area, random contamination, or biosecurity break was identified that could explain the movement of the S2308 among these animals and through the various pens.
As of March 2004, all seropositive animals on site have been euthanatized and tissue samples submitted for culture. Summaries of serial serologic and culture results and epidemiologic data will be presented. The conclusions reached may have implications for future work with brucellosis in captive wildlife facilities.