Assessing respiratory pathogen communities in bighorn sheep populations: Sampling realities, challenges, and improvements

Abstract

Respiratory disease has been a persistent problem for the recovery of bighorn sheep (Ovis canadensis), but has uncertain etiology. The disease has been attributed to several bacterial pathogens including Mycoplasma ovipneumoniae and Pasteurellaceae pathogens belonging to the Mannheimia, Bibersteinia, and Pasteurella genera. We estimated detection probability for these pathogens using protocols with diagnostic tests offered by a fee-for-service laboratory and not offered by a fee-for-service laboratory. We conducted 2861 diagnostic tests on swab samples collected from 476 bighorn sheep captured across Montana and Wyoming to gain inferences regarding detection probability, pathogen prevalence, and the power of different sampling methodologies to detect pathogens in bighorn sheep populations. Estimated detection probability using fee-for-service protocols was less than 0.50 for all Pasteurellaceae and 0.73 for Mycoplasma ovipneumoniae. Non-fee-for-service Pasteurellaceae protocols had higher detection probabilities, but no single protocol increased detection probability of all Pasteurellaceae pathogens to greater than 0.50. At least one protocol resulted in an estimated detection probability of 0.80 for each pathogen except Mannheimia haemolytica, for which the highest detection probability was 0.45. In general, the power to detect Pasteurellaceae pathogens at low prevalence in populations was low unless many animals were sampled or replicate samples were collected per animal. Imperfect detection also resulted in low precision when estimating prevalence for any pathogen. Low and variable detection probabilities for respiratory pathogens using live-sampling protocols may lead to inaccurate conclusions regarding pathogen community dynamics and causes of bighorn sheep respiratory disease epizootics. We recommend that agencies collect multiples samples per animal for Pasteurellaceae detection, and one sample for Mycoplasma ovipneumoniae detection from at least 30 individuals to reliably detect both Pasteurellaceae and Mycoplasma ovipneumoniae at the population-level. Availability of PCR diagnostic tests to wildlife management agencies would improve the ability to reliably detect Pasteurellaceae in bighorn sheep populations.

Characterizing population and individual migration patterns among native and restored bighorn sheep (Ovis canadensis)

“…In addition, we suggest a more nuanced approach to restoration and augmentation in which source populations are identified based on a suite of criteria that includes migration patterns. While disease histories and the presence of respiratory pathogens are becomingly increasingly important in informing translocations and restoration efforts (Butler et al, , ), migration patterns of source populations are not often considered, yet are known to support translocation success (Singer et al, ). Targeted management experiments that more directly link migration patterns of source populations with landscape attributes in restored areas may be an effective tool to build diversity into restored or augmented ungulate populations (Warren et al, ).…”

Is Habitat Constraining Bighorn Sheep Restoration? A Case Study

“…Given the above factors that limit natural expansion of bighorn sheep, new management strategies may be needed to increase occupation of potential habitat and thereby create larger and more robust populations. Because moving animals into novel areas or between geographically separate populations increases the risk of pathogen transmission (Butler et al 2017), an alternative restoration strategy to promote viable long‐term populations of bighorn sheep may be short‐distance translocations aimed at promoting a broader local distribution and spatially structured populations (Bleich et al 1996, Singer et al 2000 a ). Metapopulations are less vulnerable to extirpation by stochastic events than small, isolated populations (Quinn and Hastings 1987, Berger 1990, Festa‐Bianchet et al 2006).…”

Niche similarities among introduced and native mountain ungulates

“…, Butler et al. ). However, given the similarity in seasonal niches, it is likely that mountain goats will continue to increase their spatial overlap with native bighorn sheep and increase densities where the two species are sympatric presently.…”

“…Within the study area, bighorn sheep were never extirpated or augmented, and have maintained relatively stable population demographics with modest harvest rates and nearly ubiquitous presence of respiratory pathogens in sampled animals (Butler et al. ).…”

“…Although the demographic performance of bighorn sheep within the GYA is varied, the northeastern portion represents an intact and robust population that was never extirpated, has no documented widespread disease related die‐offs, and continues to show relatively stable demographic performance (Buechner , Butler et al. ).…”