Ophidiomycosis, an emerging fungal disease of snakes: Targeted surveillance on military lands and detection in the western US and Puerto Rico

Contribution of host species and pathogen clade to snake fungal disease hotspots in Europe

Infectious diseases are influenced by interactions between host and pathogen, and the number of infected hosts is rarely homogenous across the landscape. Areas with elevated pathogen prevalence can maintain a high force of infection and may indicate areas with disease impacts on host populations. However, isolating the ecological processes that result in increases in infection prevalence and intensity remains a challenge. Here we elucidate the contribution of pathogen clade and host species in disease hotspots caused by Ophidiomyces ophidiicola, the pathogen responsible for snake fungal disease, in 21 species of snakes infected with multiple pathogen strains across 10 countries in Europe. We found isolated areas of disease hotspots in a landscape where infections were otherwise low. O. ophidiicola clade had important effects on transmission, and areas with multiple pathogen clades had higher host infection prevalence. Snake species further influenced infection, with most positive detections coming from species within the Natrix genus. Our results suggest that both host and pathogen identity are essential components contributing to increased pathogen prevalence.

Genetic mechanisms and biological processes underlying host response to ophidiomycosis (snake fungal disease) inferred from tissue-specific transcriptome analyses

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.

Gene functions of the Ambystoma altamirani skin microbiome vary across space and time but potential antifungal genes are widespread and prevalent

Amphibian skin microbiomes can play a critical role in host survival against emerging diseases by protecting their host against pathogens. While a plethora of biotic and abiotic factors have been shown to influence the taxonomic diversity of amphibian skin microbiomes it remains unclear whether functional genomic diversity varies in response to temporal and environmental factors. Here we applied a metagenomic approach to evaluate whether seasonality, distinct elevations/sites, and pathogen presence influenced the functional genomic diversity of the A. altamirani skin microbiome. We obtained a gene catalogue of 92 107 nonredundant annotated genes and a set of 50 unique metagenome assembled genomes (MAGs). Our analysis showed that genes linked to general and potential antifungal traits significantly differed across seasons and sampling locations at different elevations. Moreover, we found that the functional genomic diversity of A. altamirani skin microbiome differed between B. dendrobatidis infected and not infected axolotls only during winter, suggesting an interaction between seasonality and pathogen infection. In addition, we identified the presence of genes and biosynthetic gene clusters (BGCs) linked to potential antifungal functions such as biofilm formation, quorum sensing, secretion systems, secondary metabolite biosynthesis, and chitin degradation. Interestingly genes linked to these potential antifungal traits were mainly identified in Burkholderiales and Chitinophagales MAGs. Overall, our results identified functional traits linked to potential antifungal functions in the A. altamirani skin microbiome regardless of variation in the functional diversity across seasons, elevations/sites, and pathogen presence. Our findings suggest that potential antifungal traits found in Burkholderiales and Chitinophagales taxa could be related to the capacity of A. altamirani to survive in the presence of Bd, although further experimental analyses are required to test this hypothesis.

Factors Predicting Apparent Ophidiomycosis in Wild Brown Watersnakes (Nerodia taxispilota)

Ophidiomycosis, also known as snake fungal disease, is caused by Ophidiomyces ophidiicola and is a threat to snake conservation worldwide. Ophidiomycosis has been reported throughout much of the eastern US, and outbreaks have been associated with local population declines of already strained populations. Previous studies report significant variability in ophidiomycosis among species sampled, with higher prevalence typically observed in Nerodia spp. Although ophidiomycosis can lead to morbidity and mortality in affected individuals, little is known about disease dynamics in free-ranging populations. Herein, we examine how individual-specific factors (e.g., life stage [immature, mature], contaminant status, sex, hemograms) may be associated with ophidiomycosis status in the brown watersnake (Nerodia taxispilota). During 2018-19, we sampled 97 N. taxispilota from five locations along the Savannah River in South Carolina and Georgia, US. Ophidiomyces ophidiicola DNA was detected in 66 snakes for a prevalence of 68% (95% confidence interval, 59-77). Mature snakes had a significantly higher risk of apparent ophidiomycosis (skin lesions present and quantitative PCR [qPCR], positive) relative to immature snakes. Snakes classified as having possible (skin lesions present, but qPCR negative) or apparent ophidiomycosis exhibited a relative azurophilia and heterophilia compared with individuals classified as negative (P≤0.037). Nerodia taxispilota in this region appear to have a high prevalence of apparent ophidiomycosis (22%; 95% CI, 14-31), similar to previous reports from the southeastern US. Additional epidemiologic investigations are warranted to further elucidate other individual-specific and environmental factors that may dictate disease risk and outcomes in affected populations.

Environmental temperature influences ophidiomycosis progression and survival in experimentally challenged prairie rattlesnakes (Crotalus viridis)

Ophidiomycosis is a prevalent and intermittently pervasive disease of snakes globally caused by the opportunistic fungal pathogen, Ophidiomyces ophidiicola. Host response has yet to be fully explored, including the role of temperature in disease progression and hematologic changes. This study enrolled twelve adult prairie rattlesnakes (Crotalus viridis) in an experimental challenge with O. ophidiicola at two temperatures, 26°C (n = 6) and 20°C (n = 6). Each temperature cohort included four inoculated and two control snakes. Assessments involving physical exams, lesion swabbing, and hematology were performed weekly. Differences were observed between inoculated and control snakes in survival, behavior, clinical signs, ultraviolet (UV) fluorescence, hematologic response, and histologic lesions. All inoculated snakes held at 20°C were euthanized prior to study end date due to severity of clinical signs while only one inoculated animal in the 26°C trial met this outcome. In both groups, qPCR positive detection preceded clinical signs with regards to days post inoculation (dpi). However, the earliest appearance of gross lesions occurred later in the 20°C snakes (20 dpi) than the 26°C snakes (13 dpi). Relative leukocytosis was observed in all inoculated snakes and driven by heterophilia in the 20°C snakes, and azurophilia in the 26°C group. Histologically, 20°C snakes had more severe lesions, a lack of appropriate inflammatory response, and unencumbered fungal proliferation and invasion. In contrast, 26°C snakes had marked granulomatous inflammation with encapsulation of fungi and less invasion and dissemination. The results of this study identified that O. ophidiicola-infected rattlesnakes exposed to lower temperatures have decreased survival and more robust hematologic change, though minimal and ineffective inflammatory response at site of infection. Ophidiomycosis is a complex disease with host, pathogen, and environmental factors influencing disease presentation, progression, and ultimately, survival. This study highlighted the importance of temperature as an element impacting the host response to O. ophidiicola.

Leveraging preserved specimens of Nerodia to infer the spatiotemporal dynamics of Ophidiomyces ophidiicola via quantitative polymerase chain reaction

Ophidiomyces ophidiicola (Oo) is a fungal pathogen and the causative agent of ophidiomycosis that has affected multiple snake taxa across the United States, Europe, and Asia. Ophidiomycosis has often been referred to as an emerging infectious disease (EID); however, its status as an EID has recently come under debate. Oo infections have been confirmed in wild snake populations in Texas; however, it is unknown if the pathogen is novel (i.e., invasive) or endemic to the state. To address this knowledge gap, we conducted surveys for Oo among preserved Nerodia deposited at three university museums in Texas. First, we visually assessed snakes for signs of infection (SOI), and if SOI were present, we sampled the affected area. We then used quantitative polymerase chain reaction to diagnose the presence of Oo DNA on areas with SOI and used these data to evaluate spatiotemporal patterns of Oo prevalence. We also tested for significant spatial clusters of Oo infenction using a Bernoulli probability model as implemented in the program SatScan. We found that the proportion of snakes exhibiting SOI was constant over time while the prevalence of Oo DNA among those SOI increased across space and time. Within these data, we detected an incidence pattern consistent with an introduction and then spread. We detected six spatial clusters of Oo infection, although only one was significant. Our results support the hypothesis that Oo is an emerging, novel pathogen to Texas snakes. These data narrow the knowledge gap regarding the history of Oo infections in Texas and establish a historical record of confirmed Oo detections in several counties across the state. Thus, our results will guide future research to those areas with evidence of past Oo infections but lacking confirmation in contemporary hosts.

Incidents of snake fungal disease caused by the fungal pathogen Ophidiomyces ophidiicola in Texas

The pathogen Ophidiomyces ophidiicola, widely known as the primary cause of snake fungal disease (SFD) has been detected in Texas's naïve snakes. Our team set out to characterize O. ophidiicola's spread in eastern Texas. From December 2018 until November 2021, we sampled and screened with ultraviolet (UV) light, 176 snakes across eastern Texas and detected 27. O. ophidiicola's positive snakes using qPCR and one snake in which SFD was confirmed via additional histological examination. Upon finding the ribbon snake with clear clinical display, we isolated and cultured what we believe to be the first culture from Texas. This cultured O. ophidiicola TX displays a ring halo formation when grown on a solid medium as well as cellular autofluorescence as expected. Imaging reveals individual cells within the septated hyphae branches contain a distinct nucleus separation from neighboring cells. Overall, we have found over 1/10 snakes that may be infected in East Texas, gives credence to the onset of SFD in Texas. These results add to the progress of the disease across the continental United States.

Ophidiomyces ophidiicola detection and infection: a global review on a potential threat to the world’s snake populations

Ophidiomyces ophidiicola (Oo) is one of the most relevant fungal pathogens for snakes. It is the etiological agent of ophidiomycosis, an emerging disease causing dysecdysis, skin abnormalities, crusting cutaneous lesions, and ulcerations. Despite this major tegumentary “tropism”, Oo infection can be systemic and it is capable of inducing visceral lesions. Moreover, ophidiomycosis may lead to abnormalities of reproductive physiology, hunting behavior, and thermoregulation, thus increasing the risks of sublethal effects and predation on affected snakes. Oo seems horizontally transmitted and can induce postnatal mortality. This article reviews published data on Oo detection and infection in all snake species in countries around the world and categorizes these data using new classification parameters. The presence of this fungus has been recorded in 11 states (considering the USA as a whole); however, in four states, the mycosis has only been reported in snakes held in captivity. Detection and/or infection of Oo has been ascertained in 62 snake species, divided into nine families. The taxa have been categorized with diagnostic criteria in order to report, for each species, the highest rank of categorization resulting from all cases. Therefore, 20 species have been included within the class “Ophidiomycosis and Oo shedder”, 11 within “Ophidiomycosis”, 16 in “Apparent ophidiomycosis”, and 15 within “Ophidiomyces ophidiicola present”. We also discuss the significance and limits of case classifications and Oo’s impact on wild populations, and we suggest methods for preliminary surveillance. Standardized methods, interdisciplinary studies, and cooperation between various research institutions may facilitate further Oo screening studies, elucidate the unclear aspects of the disease, and protect ophidiofauna from this emerging threat at the global level.

SEASONAL AND INTERSPECIFIC VARIATION IN THE PREVALENCE OF OPHIDIOMYCES OPHIDIICOLA AND OPHIDIOMYCOSIS IN A COMMUNITY OF FREE-RANGING SNAKES

Ophidiomycosis in snakes is caused by the fungus Ophidiomyces ophidiicola. Clinical signs associated with the disease range from minor skin lesions to severe swelling of the face. In some cases, the fungus invades the snake's underlying muscle and bone and internal organs; disease severity appears to peak during brumation. We quantified the prevalence of O. ophidiicola and ophidiomycosis in free-ranging snakes to explore seasonal variation in detection of the pathogen and disease. We collected skin swabs (n=464 samples) from seven species of free-ranging snakes (n=336) from Rondeau Provincial Park (Ontario, Canada) and tested the swabs for O. ophidiicola using quantitative PCR. We also assessed individuals for lesions consistent with ophidiomycosis and monitored changes in gross lesions over time in recaptured individuals. Eastern foxsnakes (Pantherophis vulpinus) had the highest prevalence of O. ophidiicola (24/84) and of lesions consistent with ophidiomycosis (34/84). On other species (Nerodia sipedon, Storeria dekayi, Thamnophis sirtalis, and Thamnophis sauritus), we detected the pathogen on only 4/229 snakes and observed gross lesions consistent with ophidiomycosis on 24/229 snakes. Body length of eastern foxsnakes was associated with detection of O. ophidiicola, suggesting that eastern foxsnakes' large size increases the risk of pathogen exposure relative to the other, smaller, species at our study site. Ophidiomyces ophidiicola and lesions consistent with ophidiomycosis were detected most frequently in eastern foxsnakes soon after emergence from brumation and less frequently later in the active season (O. ophidiicola: April=29.8%, October=3.9%; lesions: April=36.1%, October=5.5%). This decrease corresponded with resolution of lesions in 6/13 resampled eastern foxsnakes. Considering the seasonal cycle of O. ophidiicola and ophidiomycosis when planning disease surveillance research may improve detection probabilities for ophidiomycosis in Nearctic snakes.

REPEATED SAMPLING OF WILD INDIVIDUALS REVEALS OPHIDIOMYCES OPHIDIICOLA INFECTION DYNAMICS IN A PENNSYLVANIA SNAKE ASSEMBLAGE

Ophidiomyces ophidiicola is an emerging fungal pathogen associated with infections in snakes across North America. Although documented in Pennsylvania, O. ophidiicola has not been found at Powdermill Nature Reserve (PNR) in southwestern Pennsylvania, where the snake assemblage has been studied since 2002 and several species have recently declined. We surveyed for O. ophidiicola and putative ophidiomycosis at PNR. We screened five species of free-ranging, wild snakes (n=34) for suspected ophidiomycosis by visually checking for dermatitis and swabbing for the presence of O. ophidiicola DNA. We found a moderate prevalence of snakes with skin lesions (n=15) but a low prevalence of snakes with O. ophidiicola DNA in traditional PCR assays (n=2). Both positive snakes belonged to the same species and only one presented with lesions. When quantitative PCR screens were performed on duplicate swabs, 19 snakes were positive for O. ophidiicola DNA, with positive individuals in two species. Mark-recapture methods revealed seasonal variability in disease dynamics for sampled snakes. One individual presented with less than five skin lesions and tested negative in May 2020, had more than five lesions with a high fungal DNA load in June 2020, and no lesions with a low fungal DNA load in July 2020. We also found that snakes sampled from under the same cover object at the same time either all tested positive or all negative, including one instance involving two species. Our results underscore the value of using multiple screening techniques for O. ophidiicola surveillance and repeated sampling of individuals to understand the dynamics of ophidiomycosis in wild populations as compared to single method and single timepoint approaches.

DETECTION OF OPHIDIOMYCES OPHIDIICOLA IN THREE FILE SNAKES (ACROCHORDUS GRANULATUS) IMPORTED FROM INDONESIA TO THE MOSCOW ZOO (RUSSIA)

Three file snakes (Acrochordus granulatus) were delivered to the Moscow Zoo (Russia) from Jakarta (Indonesia). Shortly after arrival, multiple white blisters were detected on their bodies. All three snakes died within a month of arrival. On microscopy, arthrospores and mycelium were seen in exudate from the lesions. Ophidiomyces ophidiicola was isolated from two of three snakes and identified by internal transcribed spacer sequencing. Dermatophyte test medium turned red in positive cultures and can be potentially employed for detection of O. ophidiicola, the causative agent of snake fungal disease. This is the first report of O. ophidiicola in Russia and the second reported case of ophidiomycosis in file snakes. The possible source of O. ophidiicola in snakes imported from Southeast Asia is discussed.

First report of ophidiomycosis in Asia caused by Ophidiomyces ophiodiicola in captive snakes in Japan

Ophidiomycosis is an emerging infectious disease caused by the fungus Ophidiomyces ophiodiicola, which has been affecting wild and captive snakes in North America, Europe, and Australia. We report 12 cases of suspected ophidiomycosis in captive colubrid snakes in Japan. Pathological and microbiological examinations were performed, and the results confirmed the diagnosis of ophidiomycosis in two snakes, which indicated that the remaining sympatrically raised snakes also had ophidiomycosis since they exhibited similar lesions. This is the first report of ophidiomycosis in Asia caused by O. ophiodiicola. To prevent the expansion of ophidiomycosis in the natural environment in Japan, there is a need to evaluate the ophidiomycosis carrier status of imported snakes, the pathogenicity of the infection in native snakes, and the prevalence and distribution of O. ophiodiicola in wild and captive snakes. Measures also must be taken to prevent endemicity globally.