Beyond clinical signs in desert tortoises

Desert tortoise (Gopherus agassizii) population declines in the Mojave Desert in the 20th century were in part attributed to disease, particularly upper respiratory tract disease (URTD) caused by mycoplasma. Disease risk... [ view full abstract ]

Desert tortoise (Gopherus agassizii) population declines in the Mojave Desert in the 20th century were in part attributed to disease, particularly upper respiratory tract disease (URTD) caused by mycoplasma. Disease risk remains one of the concerns in desert tortoise populations when managing relocation of animals, for example due to competing habitat usage with renewable energy sites, or improving connectivity of habitat. Determining that a desert tortoise is clinically healthy and in a good body condition was one of the key requirements for tortoises at the Desert Tortoise Conservation Center (DTCC), Las Vegas, to be eligible for relocation into a designated translocation site in the Mojave Desert. One goal of this study was to determine whether URTD is the only disease of concern in tortoises at the DTCC. The other goal was to determine the correlations between clinical signs, pathologic lesions, and diagnostic test results, with focus on URTD, to identify the criteria that best predict suitability for release. Histopathology was performed on over 400 DTCC desert tortoises that were necropsied from 2009 through 2013. Standardized pre-euthanasia health assessments and molecular diagnostics were performed on a subset of these animals for comparative analysis. Necropsy revealed that URTD was a significant cause of death or euthanasia, however, pneumonia and enteritis were also seen in over 30% of the animals. Preliminary analysis suggests that nasal discharge, eroded nares, and positive Mycoplasma agassizii qPCR test results were significantly associated with presence of upper respiratory tract lesions. When assuming histopathology as the gold standard, nasal discharge had highest specificity whereas the qPCR result had highest sensitivity of individual clinical findings to detect URTD.