"Elk-to-elk transmission of this disease may be increasing in new regions of the Greater Yellowstone Ecosystem, which remains the last reservoir for brucellosis in the United States," said Paul Cross, a USGS disease ecologist and lead author of the study. He said infected animals often abort pregnancies, and the presence of the disease within livestock results in additional testing requirements and trade restrictions.
Officials said several cattle herds have been infected in Wyoming, Idaho and Montana since 2004 and recent cases of brucellosis cattle are thought to have spread from elk due to the lack of contact between bison and cattle.
"We looked at a number of hypotheses for why we may be observing these increases in brucellosis," Cross said. "Two seemed the most probable: Either brucellosis transmission among elk is becoming more frequent as elk densities increase, or the diagnostic tests are cross-reacting with another pathogen that is increasing in prevalence."
The research, conducted at the USGS Northern Rocky Mountain Science Center, was recently published in the journal Ecological Applications.