Evaluation of Serologic and Molecular Methods to Determine Disease Risk in Tortoises and Implications for Disease Management
Upper respiratory tract disease resulting from Mycoplasma infection is a primary cause of morbidity and death in desert tortoises (Gopherus agassizii), and diagnostic screening tests are essential for management of mixed-source populations.3 The two most prevalent and virulent mycoplasmas are Mycoplasma agassizii and Mycoplasma testudineum, both of which can cause debilitating disease or, at least the former, result in prolonged subclinical infections.1,2 An ELISA test specific for Mycoplasma agassizii is among the best available methods for detecting exposure of animals but does not detect active infection or pathogen shedding.4
We recently developed two quantitative real-time PCR assays for Mycoplasma agassizii and Mycoplasma testudineum and used them in conjunction with ELISA serology to screen animals at the Desert Tortoise Conservation Center (DTCC) in Las Vegas to determine the most effective testing protocol for managing the animals. Forty-five desert tortoises that died or were euthanized were necropsied and evaluated using ELISA testing for Mycoplasma agassizii antibodies on ante-mortem serum and PCR for Mycoplasma agassizii and Mycoplasma testudineum on postmortem nasal flush and nasal mucosa samples.
All PCR assays for Mycoplasma testudineum were negative. ELISA and PCR results for Mycoplasma agassizii correlated in 76% of the cases with 4.5% of cases having positive serology and negative PCR, and 20% of animals having negative serology but positive PCR. Our study showed that Mycoplasma testudineum has a relatively low prevalence at the DTCC and that using both ELISA and PCR assays together is necessary for maximizing management and release strategies.
This work was funded in part by the U.S. Fish and Wildlife Service.
1. Brown DR, Merritt JL, Jacobson ER, Klein PA, Tully JG, Brown MB. Mycoplasma testudineum sp. nov., from a desert tortoise (Gopherus agassizii) with upper respiratory tract disease. Int J Syst Evol Micr. 2004;54:1527–1529.
2. Brown MB, Schumacher IM, Klein PA, Harris K, Correll T, Jacobson ER. Mycoplasma agassizii causes upper respiratory tract disease in the desert tortoise. Infect Immun. 1994;62:4580–4586.
3. Jacobson ER, Gaskin JM, Brown MB, Harris RK, Gardiner CH, LaPointe JL, et al. Chronic upper respiratory tract disease of free-ranging desert tortoises (Xerobates agassizii). J Wildl Dis. 1991;27:296–316.