The slow dynamics of mycoplasma infections in a tortoise host reveal heterogeneity pertinent to pathogen transmission and monitoring

C M Aiello,P G Emblidge,P J Hudson,K E Nussear,T C Esque

doi:10.1017/s0950268818002613

Abstract

The epidemiology of infectious diseases depends on many characteristics of disease progression, as well as the consistency of these processes across hosts. Longitudinal studies of infection can thus inform disease monitoring and management, but can be challenging in wildlife, particularly for long-lived hosts and persistent infections. Numerous tortoise species of conservation concern can be infected by pathogenic mycoplasmas that cause a chronic upper respiratory tract disease (URTD). Yet, a lack of detailed data describing tortoise responses to mycoplasma infections obscures our understanding of URTDs role in host ecology. We therefore monitored Mycoplasma agassizii infections in 14 captive desert tortoises and characterised clinical signs of disease, infection intensity, pathogen shedding and antibody production for nearly 4 years after initial exposure to donor hosts. Persistent infections established in all exposed tortoises within 10 weeks, but hosts appeared to vary in resistance, which affected the patterns of pathogen shedding and apparent disease. Delays in host immune response and changes to clinical signs and infection intensity over time resulted in inconsistencies between diagnostic tools and changes in diagnostic accuracy throughout the study. We discuss the implications these results have for URTD epidemiology and past and future research assessing disease prevalence and dynamics in tortoise populations.

Highlights

IntroductionThe kinetics of pathogen growth and host response can shape population-level disease patterns [1]
Following initial infection, the kinetics of pathogen growth and host response can shape population-level disease patterns [1]
We conducted this study at the Desert Tortoise Conservation Center (DTCC), Clark County, Nevada, USA – an outdoor captive facility constructed within native creosote-bursage desert scrub

Summary

Introduction

The kinetics of pathogen growth and host response can shape population-level disease patterns [1]. Estimating temporal variation in infection parameters and the distribution of possible host responses are important first steps to model and manage infectious diseases. In wildlife, these infection dynamics can be difficult to estimate as individuals are often sampled infrequently, timing of infection is typically unknown and reliable diagnostic tests may be unavailable. Identified bacterial pathogens, Mycoplasma agassizii and M. testudineum, can cause a chronic upper respiratory tract disease (URTD) in tortoises within the genus Gopherus [10], which can lead to mortality but more often results in long-term morbidity. Standardised health assessments and robust diagnostic tools only recently became widespread in this system, and so many of the basic attributes of URTD infection and epidemiology have not been thoroughly quantified [14]

Methods

Results

Conclusion