26th Annual Meeting and Symposium of the
Desert Tortoise Council, March 16-18, 2001
Abstracts

Clinical Disease and Laboratory Abnormalities in Free-Ranging Desert Tortoises (Gopherus agassizii) in California (1990-1995)

Mary M. Christopher¹, Kristin H. Berry², B. T. Henen³, and K. A. Nagy^3
1Department of Pathology, Microbiology & Immunology, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616
²U.S. Geological Survey, Western Ecological Research Center, Riverside, CA 92507
³Department of Biology and Laboratory of Biomedical and Environmental Sciences, University of California-Los Angeles, Los Angeles, CA 90024

Desert tortoise (Gopherus agassizii) populations have experienced precipitous declines resulting from the cumulative impact of habitat loss, and human and disease-related mortality. Diagnosis of disease in live, free-ranging tortoises is facilitated by evaluation of clinical signs and laboratory test results but may be complicated by seasonal and environmental effects. The goals of this study were: to document and monitor clinical signs of disease in adult, free-ranging desert tortoises at three sites in the Mojave Desert of California between October 1990 and October 1995; to determine the association of clinical signs with hematological, biochemical, serological and microbiological test results; to characterize disease patterns by site, season, and sex; and to assess the utility of diagnostic tests in predicting morbidity and mortality. Venous blood samples were obtained four times per year from tortoises of both sexes at the Desert Tortoise Research Natural Area (DTNA), Goffs, and Ivanpah Valley. Tortoises were given a complete physical examination, and clinical abnormalities were graded by type and severity. Of 108 tortoises, 68.5% had clinical signs of upper respiratory disease consistent with mycoplasmosis, and 85.4% had shell lesions consistent with cutaneous dyskeratosis. Oral ulcers were noted in 23% of tortoises at Goffs and in two Ivanpah tortoises. Tortoises with ulcers were significantly more likely to have positive nasal cultures for Mycoplasma agassizii (P<.0001). Six tortoises had marked azotemia (BUN > 100 mg/dl); of these, three died, and two had necropsy confirmation of urinary tract disease. Tortoises at Goffs were significantly more likely to have moderate to severe shell disease, positive nasal cultures for Mycoplasma agassizii, heteropenia, and increased serum AST activity than tortoises at other sites. Tortoises at DTNA were significantly more likely to be seropositive for M. agassizii and to have lymphocytosis or heterophilia. Ivanpah tortoises were more likely to have moderate to heavy Pasteurella testudinis growth in nasal cultures, heterophilia, and hypophosphatemia. Specific laboratory or clinical abnormalities were poorly predictive of morbidity and mortality. The severe disease abnormalities in Goffs tortoises have likely contributed to the population decline that occurred during and subsequent to this study.