Mycoplasmal Upper Respiratory Tract Disease Across the Range of the Threatened Mojave Desert Tortoise: Associations with Thermal Regime and Natural Antibodies

Abstract

Most research of upper respiratory tract disease (mycoplasmal URTD) in the threatened Mojave Desert tortoise (Gopherus agassizii) has worked under the hypothesis that the pathogen, Mycoplasma agassizii, has a relatively consistent and predictable effect on tortoise populations across their natural range. In contrast, we hypothesized that multiple factors influence the prevalence of disease and analyzed biological and environmental variables that vary significantly across the Mojave Desert. We used multiple regression models to analyze associations between mycoplasmal URTD and the genetic structure of 24 tortoise populations, levels of natural antibody (NAb) to M. agassizii in tortoises (one component of the innate immune system), precipitation, and colder thermal regimes. We detected a significant, positive association between mean levels of NAb and seroprevalence to M. agassizii. We hypothesized that NAbs may provide tolerance to mycoplasmal infections and that more tolerant populations may act as host reservoirs of disease. We also detected significant associations between colder winters and mycoplasmal URTD, suggesting that colder winters may depress tortoise immune resistance against M. agassizii or enhance conditions for the growth of M. agassizii.

Host contact and shedding patterns clarify variation in pathogen exposure and transmission in threatened tortoiseGopherus agassizii: implications for disease modelling and management

“…; Sandmeier et al . ). If the apparent majority of contacts in the wild have low transmission probability as we observed, low infection prevalence would be expected compared to a captive situation where contact rates and durations are amplified.…”

Biology and Diseases of Reptiles

“…with respiratory disease in snakes, tortoises, and turtles (Penner et al, 1997;Jacobson et al, 1991a;Sandmeier et al, 2013;Guthrie et al, 2013). Geographically, M. tes tudineum seems to have a similar distribution to, but a lower prevalence than, M. agassizii in desert and gopher tortoises across North America.…”

“…Geographically, M. tes tudineum seems to have a similar distribution to, but a lower prevalence than, M. agassizii in desert and gopher tortoises across North America. Mycoplasma exhibits interspecies transmission, and cold weather has been shown to decrease the resistance of Mojave desert tortoises to infection (Sandmeier et al, 2013). Mycoplasma exhibits interspecies transmission, and cold weather has been shown to decrease the resistance of Mojave desert tortoises to infection (Sandmeier et al, 2013).…”

Lag of Immunity Across Seasonal Acclimation States in Gopher Tortoises (Gopherus Polyphemus)

“…Sandmeier et al. () found a positive relationship between severe winter weather and markers of upper respiratory tract disease in Mojave Desert Tortoises ( Gopherus agassizii ). Additionally, telemetry studies have indicated that disease may be an important constraint on Gopher Tortoises ( Gopherus polyphemus ) during winter, when diseased individuals were found to leave their burrows during cold weather (McGuire et al., ).…”