EPIDEMIOLOGY OF CHRONIC WASTING DISEASE IN CAPTIVE ROCKY-MOUNTAIN ELK

Between June 1986 and May 1997, chronic wasting disease (CWD) was the only natural cause of adult mortality among captive Rocky Mountain elk (Cervus elaphus,nelsoni) held at a wildlife research facility near Fo rt Collins, Colorado (USA). Of 23 elk that remained in this herd >15 m o, four (17%) developed CWD. All affected elk were unrelated females f rom the founding cohort, captured as neonates and raised in 1986. The index case was diagnosed in 1989; time intervals between subsequent ca ses ranged from 13 to 32 mo. Initial age at onset of clinical signs ra nged from about 2.9 to 8.1 yr; duration of clinical disease ranged fro m 5 to 12 mo (mean = 7.5 mo) prior to death. Intraspecific lateral tra nsmission of CWD seemed the most plausible explanation for the epidemi c pattern observed; neither periparturient nor maternal transmission a ppeared necessary to sustain this outbreak. Early detection and elimin ation of incubating or clinical individuals may have aided in reducing exposure or infection rates as compared to a previous outbreak in the same facility. Transmission routes and rates, pathogenesis, antemorte m diagnostic tools, and the potential role of reservoirs or environmen tal contamination in perpetuating CWD epidemics warrant further invest igation.