Abstract:
Ecological context—the biotic and abiotic environment, along with its influence on
population mixing dynamics and individual susceptibility—is thought to have major
bearing on epidemic outcomes. However, direct comparisons of wildlife disease
events in contrasting ecological contexts are often confounded by concurrent dif ferences in host genetics, exposure histories, or pathogen strains. Here, we compare
disease dynamics of a Mycoplasma ovipneumoniae spillover event that affected big horn sheep populations in two contrasting ecological contexts. One event occurred
on the herd's home range near the Rio Grande Gorge in New Mexico, while the other
occurred in a captive facility at Hardware Ranch in Utah. While data collection regi mens varied, general patterns of antibody signal strength and symptom emergence
were conserved between the two sites. Symptoms appeared in the captive setting
an average of 12.9 days postexposure, average time to seroconversion was 24.9 days,
and clinical signs peaked at approximately 36 days postinfection. These patterns were
consistent with serological testing and subsequent declines in symptom intensity in
the free-ranging herd. At the captive site, older animals exhibited more severe de clines in body condition and loin thickness, higher symptom burdens, and slower an tibody response to the pathogen than younger animals. Younger animals were more
likely than older animals to clear infection by the time of sampling at both sites. The
patterns presented here suggest that environment may not be a major determinant
of epidemiological outcomes in the bighorn sheep—M. ovipneumoniae system, elevat ing the possibility that host- or pathogen-factors may be responsible for observed
variation.
