Search

Emerging infectious diseases in wildlife species caused by pathogenic fungi are of growing concern, yet crucial knowledge gaps remain for diseases with potentially large impacts. For example, there is detailed knowledge about host pathology and mechanisms underlying response for chytridiomycosis in amphibians and white‐nose syndrome in bats, but such information is lacking for other more recently described fungal infections. One such disease is ophidiomycosis, caused by the fungus Ophidiomyces ophidiicola, which has been identified in many species of snakes, yet the biological mechanisms and molecular changes occurring during infection are unknown. To gain this information, we performed a controlled experimental infection in captive Prairie rattlesnakes (Crotalus viridis) with O. ophidiicola at two different temperatures: 20 and 26°C. We then compared liver, kidney, and skin transcriptomes to assess tissue‐specific genetic responses to O. ophidiicola infection. Given previous histopathological studies and the fact that snakes are ectotherms, we expected highest fungal activity on skin and a significant impact of temperature on host response. Although we found fungal activity to be localized on skin, most of the differential gene expression occurred in internal tissues. Infected snakes at the lower temperature had the highest host mortality whereas two‐thirds of the infected snakes at the higher temperature survived. Our results suggest that ophidiomycosis is likely a systemic disease with long‐term effects on host response. Our analysis also identified candidate protein coding genes that are potentially involved in host response, providing genetic tools for studies of host response to ophidiomycosis in natural populations. [ABSTRACT FROM AUTHOR]

Ophidiomycosis, caused by the fungus Ophidiomyces ophidiicola, poses a threat to the health of wild and managed snakes worldwide. Variation in snake innate immunity, the primary defense against infection in reptiles, may explain the observed variation in ophidiomycosis clinical disease severity among snakes. In this study, two components of the innate immune response were examined in snake plasma. We investigated whether complement activity, as measured by sheep red blood cell hemolysis, and chitotriosidase activity were associated with ophidiomycosis disease severity and time in captivity in Lake Erie watersnakes (Nerodia sipedon insularum). There was no difference in complement-mediated hemolysis or chitotriosidase activities between snakes with varying levels of ophidiomycosis clinical severity sampled in the field. However, among snakes with skin lesions kept in captivity, chitotriosidase activity was significantly higher in snakes with mild disease, compared with snakes with severe disease, and hemolysis activity increased with time in captivity. Overall, Lake Erie watersnakes had higher complement activity, but lower chitotriosidase activity, compared with other reptile species. To our knowledge, this study is the first to describe chitotriosidase activity in a snake species. These results provide mixed evidence of associations between innate immune function and ophidiomycosis severity, and more work is needed to investigate differences among snake species. [ABSTRACT FROM AUTHOR]

Ophidiomycosis, an infectious disease of snakes caused by the fungus Ophidiomyces ophidiicola, is known to cause skin lesions and, in some cases, deeper infections, and even death. It has been documented in captive snakes worldwide and in free-ranging snakes in the United States and Europe. Diagnostic limitations have impeded characterization of the epidemiology of this disease and subsequent efforts to improve clinical care and conservation outcomes. The purpose of this research was to evaluate the efficacy of qPCR of snake sheds as a noninvasive diagnostic tool for the detection of O. ophidiicola, compared to swabs prior to and following the shed. We tested shed pieces from grossly observed skin lesions or mid body sections if disease was not obvious, and matched skin swabs from 68 animals using a qPCR assay specific for O. ophidiicola. There was nearly complete agreement between the qPCR results of sheds and swabs (Cohen's kappa = 0.97) and sheds were 100% sensitive and 97% specific for apparent ophidiomycosis, with a 97% negative predictive value and a 100% positive predictive value. Our results indicate that qPCR of snake sheds is a reliable detection method for the presence of O. ophidiicola, as this technique has high agreement with peri-ecdysis skin swabbing. Although this technique can be used for noninvasive pathogen detection in captive individuals with known histories, results from snake sheds from free-ranging animals with no knowledge of associated clinical signs should be interpreted with caution and additional surveillance is necessary in these cases. [ABSTRACT FROM AUTHOR]

Ophidiomycosis, commonly called snake fungal disease, has been linked to significant morbidity of free-ranging snakes in North America and Europe. Diagnosis of ophidiomycosis currently requires detection of skin lesions via physical exam or characteristic histopathology as well as detection of the causative agent, Ophidiomyces ophidiicola, through quantitative (q)PCR or fungal culture of a skin swab or tissue sample. While reliable, these methods require specialized training, invasive procedures (e.g., biopsy), and several days or weeks to receive results. Additionally, screening entire populations can quickly become costly. A fast, easy-to-use, cost-efficient, and sensitive screening tool is needed to optimize conservation strategies and treatment intervention. Our objective was to investigate the association between skin fluorescence under long-wave ultraviolet (UV) light (365 nm) and the detection of Ophidiomyces ophidiicola DNA using qPCR. Fifty-eight Lake Erie watersnakes (Nerodia sipedon insularum) collected in June of 2018 and 2019 from islands in western Lake Erie, Ottawa County, Ohio, US were visually inspected for skin lesions, photographed under natural light and UV light, and swabbed for qPCR analysis. Fluorescence was highly associated with the presence of skin lesions, and the presence of at least one fluorescent skin lesion was 86% sensitive and 100% specific for identifying animals with apparent ophidiomycosis, with a positive predictive value of 100%. While we recommend performing standard diagnostics along with fluorescence, our study supports the use of visual UV fluorescence identification as a preliminary, affordable, noninvasive, and field-applicable method to screen populations for ophidiomycosis. [ABSTRACT FROM AUTHOR]