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

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.

Ecological conditions predict the intensity of Hendra virus excretion over space and time from bat reservoir hosts

“…AUC has previously been used to summarise the cumulative pathogen output from within‐host dynamics (e.g. Mycoplasma agassizii intensity across individual tortoises; Aiello et al, 2019) and number of infected individuals (e.g. fungal infections across Daphnia populations; Penczykowski et al, 2014; Shocket et al, 2018), which capture host infectiousness and local epidemic size, respectively, rather than the explicit infectious dose available to recipient hosts.…”

Ecological conditions experienced by bat reservoir hosts predict the intensity of Hendra virus excretion over space and time

“…Here, we propose the area under annual shedding curves (i.e., AUC) as a meaningful metric to summarize pathogen output into the environment. AUC has previously been used to summarize the cumulative pathogen output from within-host dynamics (e.g., Mycoplasma agassizii intensity across individual tortoises [68]) and number of infected individuals (e.g., fungal infections across Daphnia populations [69,70]), which capture host infectiousness and local epidemic size, respectively, rather than the explicit infectious dose available to recipient hosts. For the latter, epidemic size has in turn been linked to local ecological conditions, such as lake temperature and host community composition [69,70]; however, such metrics have not been applied to replicate reservoir host populations to identify predictors of pathogen pressure.…”

Complex immune responses and molecular reactions to pathogens and disease in a desert reptile (Gopherus agassizii)

“…Uninfected tortoises ( n = 10) were classified as clinically normal, and negative for serological immune responses and presence of Myag and Myte in the oral cavity. Tortoises were evaluated and sampled monthly for six months prior to our experiment to confirm the clinical, immunological, and infection condition of each animal (Aiello, Esque, Nussear, Emblidge, & Hudson, ; Aiello et al, ). On 16 August 2013, one infected tortoise was randomly assigned and added to one of five enclosures housing two uninfected tortoises (hereafter referred to as “exposed” tortoises).…”