In October, MiDOG received samples from roughly 20 turtles across the country suffering from unexplained shell infections. Next-generation sequencing (NGS) revealed that all samples contained high levels of a fungal species belonging to the genus Emydomyces. Notably, the Emydomyces sequences detected across all turtles were genetically identical, suggesting they originate from the same species.
Only one species in this genus Emydomyces testavorans has been formally described to date (1). However, the Emydomyces sp. identified in these turtles shared only ~90% genetic identity with E. testavorans, indicating that the pathogen belongs to the same genus but is likely a distinct and previously undocumented species.
E. testavorans – an emerging shell disease of turtles
Emydomyces testavorans was first reported in turtles in Washington State, where animals presented with a mysterious ulcerative shell disease. Genetic analysis showed the pathogen was <92% identical to known fungal species in the family Onygenaceae, leading researchers to classify it as a new genus in 2019 (1). Since its discovery, E. testavorans has been associated with active shell lesions in both wild and captive turtles and terrapins (1–3).
Lesions linked to E. testavorans typically begin on the shell and may progress into the underlying bone. Infected animals can show a wide range of clinical signs, including shell ulcerations, pitted depressions, discoloration, flaking, increased shell pliability, nodular masses, and cystic lesions. In severe cases, the infection can disseminate and may be fatal (4). Some animals, however, may remain asymptomatic carriers.
Challenges in Detecting E. testavorans
Diagnosing E. testavorans is notably difficult. Traditional culture methods often fail due to rapid bacterial overgrowth and competition from environmental fungi. As a result, detection currently relies heavily on PCR-based assays, and at least two separate qPCR tests are recommended to reduce the risk of false negatives (5).
Implications of a New Emydomyces Species
To date, E. testavorans infections have been reported primarily in Washington, with sporadic detections in California and Illinois (1,3,6). Treatment options remain under investigation, though terbinafine has shown promise.
The discovery of a genetically distinct novel Emydomyces species across the United States raises important questions about emerging fungal diseases in turtles. Shell disease is a major threat to turtle health, and the discovery of a new fungal pathogen highlights the importance of careful monitoring and accurate pathogen identification.
How MiDOG Helps Detect Emerging Pathogens
Given the culturing challenges associated with E. testavorans and related fungi, the MiDOG NGS test is particularly well-suited for detecting novel microbial threats. MiDOG’s sequencing-based approach:
- Identifies microbes independent of their ability to grow in culture
- Overcomes limitations caused by bacterial and fungal overgrowth
- Detects pathogens even when the causative agent is unknown
- Can identify novel or highly divergent species that targeted PCR assays may miss
With approximately 99% of microbes being unculturable, comprehensive sequencing provides a critical advantage in diagnosing and monitoring emerging infectious diseases. Detecting this previously unrecognized Emydomyces species demonstrates the value of MiDOG’s approach in identifying new or unusual pathogens.
References:
- Woodburn, D. B., Miller, A. N., Allender, M. C., Maddox, C. W., & Terio, K. A. (2019). Emydomyces testavorans, a new genus and species of onygenalean fungus isolated from shell lesions of freshwater aquatic turtles. Journal of clinical microbiology, 57(2), 10-1128.
- Woodburn, D. B., Kinsel, M. J., Poll, C. P., Langan, J. N., Haman, K., Gamble, K. C., … & Terio, K. A. (2021). Shell lesions associated with Emydomyces testavorans infection in freshwater aquatic turtles. Veterinary pathology, 58(3), 578-586.
- Lambert, M. R., Hernández-Gómez, O., Krohn, A. R., Mutlow, A., Patterson, L., Rosenblum, E. B., … & Bushell, J. (2021). Turtle shell disease fungus (Emydomyces testavorans): first documented occurrence in California and prevalence in free-living turtles. Ichthyology & Herpetology, 109(4), 958-962.
- Emerging turtle disease, Emydomyces testavorans. Emerging Turtle Disease, Emydomyces Testavorans – Veterinary Medicine at Illinois
- Moorhead, K. A., Burke, D. M., Adamovicz, L. A., Anchor, G. C., Graser, W., Glowacki, G., & Allender, M. C. (2025). Characterizing the Performance of Multiple Testing Modalities to Detect Emydomyces testavorans in Blanding’s Turtles (Emydoidea blandingii). The Journal of Wildlife Diseases.
- Fredrickson, K., Adamovicz, L., Terio, K., Davidson, A., Ryan, M., Waligora, M., … & Allender, M. C. (2024). Emydomyces testavorans surveillance in multiple free-ranging terrestrial and aquatic chelonian species in Illinois, USA. The Journal of Wildlife Diseases, 60(4), 850-859.