BRUCELLOSIS TRANSMISSION BETWEEN WILDLIFE AND LIVESTOCK IN THE GREATER YELLOWSTONE ECOSYSTEM: INFERENCES FROM DNA GENOTYPING

Michael Patrick O'Brien, The University of Montana

Abstract

Brucellosis transmission between wildlife species and cattle in the greater Yellowstone ecosystem has been difficult to assess because the causative agent Brucella abortus bacteria is extremely difficult to isolate for DNA genotyping. We examined transmission of B. abortus between bison, elk, and cattle using nine variable-number tandem repeat (VNTR) markers on DNA from 98 isolates of B. abortus recovered from elk, bison, and cattle. All specimens were from geographically distinct populations in Idaho, Montana, and Wyoming. A haplotype network consisting of 54 individual haplogroups was generated from these isolates using Network v4.61. Network assessments of genetic relatedness among Brucella isolates showed that genotypes from the 2008 cattle outbreak in Wyoming matched elk B. abortus genotypes, confirming elk as the likely source. Network assessments showed substantial interspecific transmission between elk and bison populations in Montana. The B. abortus from the two recent outbreaks (2007, 2008) in Montana cattle had genotypes similar to isolates from both bison and elk. Because wild bison have been excluded from the Montana cattle areas for decades as part of wildlife management policy, our findings suggest transmission likely occurred between bison and elk in Yellowstone before eventually being transmitted to cattle in southern Montana. Finally, the occurrence of identical B. abortus genotypes between individual Montana elk suggests that brucellosis might have recently become established in Montana, either by transmission from northern Yellowstone bison or from infected elk immigrants from Wyoming.