Effects of Management and Climate on Elk Brucellosis in the Greater Yellowstone Ecosystem

Abstract

Every winter, government agencies feed approximately 6000 metric tons (6 x 10(6) kg) of hay to elk in the southern Greater Yellowstone Ecosystem (GYE) to limit transmission of Brucella abortus, the causative agent of brucellosis, from elk to cattle. Supplemental feeding, however, is likely to increase the transmission of brucellosis in elk, and may be affected by climatic factors, such as snowpack. We assessed these possibilities using snowpack and feeding data from 1952 to 2006 and disease testing data from 1993 to 2006. Brucellosis seroprevalence was strongly correlated with the timing of the feeding season. Longer feeding seasons were associated with higher seroprevalence, but elk population size and density had only minor effects. In other words, the duration of host aggregation and whether it coincided with peak transmission periods was more important than just the host population size. Accurate modeling of disease transmission depends upon incorporating information on how host contact rates fluctuate over time relative to peak transmission periods. We also found that supplemental feeding seasons lasted longer during years with deeper snowpack. Therefore, milder winters and/or management strategies that reduce the length of the feeding season may reduce the seroprevalence of brucellosis in the elk populations of the southern GYE.

Deer density and disease prevalence influence transmission of chronic wasting disease in white‐tailed deer

“…Aggregation of individuals and groups increases potential disease transmission (Cross et al 2007), and seasonal aggregation of white-tailed deer groups occurs more frequently in open agricultural landscapes than in heavily forested landscapes (Hirth 1977, Nixon et al 1991, Mandujano and Gallina 1996, Lingle 2003. Additionally, deer home range size is inversely related to habitat heterogeneity (Kie et al 2002, Saïd and Servanty 2005, Skuldt 2005, Walter et al 2009), and overlap of social groups may decrease as home range size v www.esajournals.org decreases, potentially reducing infectious contact.…”

Status of Brucellosis in Free-Ranging Elk and Bison in Wyoming

“…Transmission of brucellosis typically occurs orally when susceptible animals contact infected aborted fetuses, fetal membranes and fluids, or uterine discharges (Thorne, 2001). Supplemental winter feeding of elk congregates animals on feedgrounds from November through April, overlapping the period of peak brucellosis transmission from February through June (Roffe et al, 2004;Cross et al, 2007). Maichak et al (2009) documented that up to 12% of elk attending feedgrounds contacted pseudo-aborted elk fetuses placed on feedground sites.…”

A multi‐scale assessment of animal aggregation patterns to understand increasing pathogen seroprevalence

“…Therefore, we hypothesized that rates of increasing brucellosis seroprevalence will be more related to group sizes in the tail of the distribution than annual population density or mean group size. In addition, previous work on feedground elk showed brucellosis seroprevalence was higher in feedgrounds that operated later into the spring and for longer periods (Cross et al 2007). Therefore, we also hypothesized that rates of increasing brucellosis would be related to the tail of the group size distribution observed during the end of the transmission period (end of period elk are found on the winter range) and to the average of monthly elk densities across the transmission period.…”

“…We used this measure because elk on a winter range with consistently higher densities throughout the transmission period (February-May) may have a higher probability of infection than elk on a winter range where densities fluctuate because elk are migrating to the winter range late or departing for summer range early (Cross et al 2007).…”