Terbinafine trial shows mixed results in Blanding’s turtles

A new American Journal of Veterinary Research clinical trial suggests that bioencapsulated terbinafine may be less dependable in practice than earlier pharmacokinetic data had implied for treating Emydomyces testavorans in Blanding’s turtles. In the 12-month study, naturally infected turtles received oral terbinafine at 30 mg/kg in earthworms every 48 hours, but the reported outcome was inconsistent resolution rather than reliable clearance, making this an important update for clinicians and conservation programs managing shell disease in chelonians. (experts.illinois.edu)

That finding matters because the treatment concept had a reasonable scientific basis. In a 2023 AJVR study in western pond turtles, investigators found that bioencapsulation in earthworms was a feasible delivery method and produced higher terbinafine exposure than oral gavage, with most turtles in the bioencapsulated phase predicted to remain above the reported minimum inhibitory concentration for E. testavorans during dosing intervals. But the authors of that earlier paper explicitly cautioned that clinical studies were still needed to determine whether those concentrations translated into efficacy. The new Blanding’s turtle trial appears to answer that question with a more mixed result. (experts.illinois.edu)

The broader disease backdrop also helps explain why this matters beyond a single protocol. E. testavorans was only formally described in 2019 as a novel onygenalean fungus isolated from shell lesions of freshwater turtles, and susceptibility testing in that report suggested activity for several antifungals, including terbinafine. Since then, the pathogen has been linked with ulcerative shell disease and recognized as a conservation concern in managed and wild chelonian populations. (pmc.ncbi.nlm.nih.gov)

In Illinois, where Blanding’s turtles are conservation priority animals, the fungus has already affected head-start and managed populations. Lake County Forest Preserves said some captive Blanding’s turtles in its recovery program were found infected in 2022 and were held back from release to limit spread. The agency later described treatment efforts as promising in that setting, with more than 50 of 60 captive turtles reportedly testing negative, but that account involved a different protocol centered on terbinafine baths rather than the long-term oral bioencapsulation approach assessed in the AJVR trial. That distinction is important: encouraging field-program updates should not be assumed to validate a specific drug-delivery method studied under controlled conditions. (lcfpd.org)

Diagnostic uncertainty is another key part of the story. A 2025 Journal of Wildlife Diseases study on Blanding’s turtles found that E. testavorans can be difficult to detect antemortem and recommended qPCR-based surveillance strategies tailored to the management setting. Combined cloacal-oral-shell swab qPCR and water qPCR both performed well for routine surveillance, while paired COSS testing maximized sensitivity when missing infected animals would be especially costly. For clinicians and program veterinarians, that means “treatment success” may be hard to define without repeated, structured follow-up testing. (experts.illinois.edu)

Expert commentary in the public domain has also reflected how unsettled treatment remains. The University of Illinois wildlife team has said treatment for shell disease secondary to E. testavorans is still being investigated and has pointed to nebulized terbinafine as a potentially helpful adjunct, especially when combined with systemic antifungal therapy delivered in repeated intervals. That doesn’t establish a standard of care, but it does reinforce the idea that monotherapy, route of administration, lesion burden, tissue penetration, and duration all likely influence outcomes. (vetmed.illinois.edu)

Why it matters: For veterinary professionals, especially those in exotics, zoological medicine, and conservation medicine, this study is a caution against overinterpreting pharmacokinetic promise as clinical proof. Bioencapsulation may still be valuable for compliance and stress reduction in turtles that are difficult to medicate, but inconsistent resolution over a year suggests that case management may need to include multimodal treatment plans, repeat diagnostics, environmental control, and conservative release criteria for head-start or quarantine populations. That is especially relevant where false clearance could affect both individual patients and population-level recovery efforts. (experts.illinois.edu)

What to watch: The next steps will likely include publication of the full AJVR efficacy dataset, more detail on plasma concentration findings from the Blanding’s turtle cohort, and comparative work on oral, topical, bath, or nebulized terbinafine protocols, potentially alongside improved surveillance frameworks for confirming true clearance before release or transfer. (experts.illinois.edu)