Document Type

Dissertation - Open Access

Award Date

2020

Degree Name

Doctor of Philosophy (PhD)

Department / School

Natural Resource Management

First Advisor

Jonathan A. Jenks

Keywords

Bighorn sheep, Chronic carrier, Cross-strain transmission, Mycoplasma ovipneumoniae, Respiratory disease, Unilateral colonization

Abstract

Infectious respiratory disease has long been identified as the cause of bighorn sheep (Ovis canadensis) historical declines and extirpations, and Mycoplasma ovipneumoniae (Movi) is the primary pathogen inducing disease and mortality. Population-level effects of pneumonia events range from mild to extirpation. Variable individual response to pathogen exposure emerges from dynamic interactions between competing evolutionary processes within the host and pathogen. Understanding impacts of this evolutionary warfare is essential to assessing long-term impacts of pathogen invasion and developing appropriate countermeasures to protect population health. Freeranging populations are faced with spillover infections from domestic sheep and goats as well as previously infected conspecifics. The introduction of a novel Movi strain from a spillover event can result in high all-age morbidity and subsequent mortality. We studied the effects of indirect and direct infection of captive bighorn sheep with Movi, a genetically diverse pathogen. We also used known Movi-carriage histories to classify ewes into 1 of 3 Movi carrier classes. We tested the hypothesis that respiratory disease persistence within bighorn sheep populations is driven by chronically Movi infected ewes, and the prediction that lambs born in pens with at least one chronic carrier ewe (treatment) would experience Movi-induced pneumonia mortality whereas lambs born in pens without a chronic carrier ewe (control) would not develop fatal pneumonia. When all mortality causes were pooled across all years of our study, the percentage of lambs that did not survive was more than twice as high when lambs were in born in pens containing at least one Movi chronic shedder ewe (treatment), compared to when only Movi negative and/or intermittent ewes were present in the pen (control; 92% (n = 33 of 36) and 38% (n = 5 of 13). The mean probability of pneumonia-induced mortality for commingled lambs was above 0.75 by 15 days of age and generally remained above that level for the duration of the study. Our model also estimated this probability to be elevated (≥ 0.90) as early as 16 days of age until 45 days of age, and a secondary peak for older, nearly weaned, lambs (105–114 days of age). While conducting a study for Movi detection probability in serial samples, we document unilateral Movi colonization and direct managers on field sampling techniques for reliable disease surveillance of bighorn sheep populations. Our results suggest that active disease control efforts must account for multiple Movi strains to prevent spillover epidemics. Our results also underscore that removal of chronic carriers from a population will aid bighorn sheep recovery efforts.

Library of Congress Subject Headings

Bighorn sheep -- Respiratory organs -- Diseases.
Mycoplasma diseases in animals.
Pneumonia.

Format

application/pdf

Number of Pages

163

Publisher

South Dakota State University

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Rights Statement

In Copyright