International overview of sea turtle fibropapillomatosis: a survey of expert opinions and trends

Introduction

Marine environments offer a wealth of opportunities to improve understanding and treatment options for cancers, through insights into a range of fields from drug discovery to mechanistic insights. By applying One Health principles the knowledge obtained can benefit both human and animal populations, including marine species suffering from cancer. One such species is green sea turtles (Chelonia mydas), which are under threat from fibropapillomatosis (FP), an epizootic tumor disease (animal epidemic) that continues to spread and increase in prevalence globally. In order to effectively address this epizootic, a more thorough understanding is required of the prevalence of the disease and the approaches to treating afflicted turtles.

Methods

To identify knowledge gaps and assess future needs, we conducted a survey of sea turtle FP experts. The survey consisted of 47 questions designed to assess general perceptions of FP, the areas where more information is needed, local FP trends, the disease status, and mitigation needs, and was voluntarily completed by 44 experts across a broad geographic range.

Results

Over 70% of respondents both recognized FP as a cancerous panzootic disease, and reported that FP is increasing in prevalence. They report several factors contributing to this increase. Nearly all of the respondents reported that FP research, patient treatment and rehabilitation required more funding in their area, and reported inadequate facilities and capacity for dealing with FP patients. Treatment approaches varied: just over 70% of the medical experts that responded surgically remove FP tumors, either using laser or scalpel. Just under half of respondents use anti-cancer drugs in their treatment of FP. Internal tumors were reported as justification for euthanasia by 61.5% of respondents, and 30.8% reported severe external tumors to be sufficient grounds for euthanasia. Most medical respondents (93.3%) routinely perform necropsy on deceased or euthanized FP-afflicted turtles. Over 80% of respondents considered large-scale multidisciplinary collaboration 'extremely important' for advancing the field of FP research.

Discussion

The survey responses provide a valuable insight into the current status of FP in sea turtles, FP treatment, rehabilitation and research, and help to identify critical FP-related areas most in need of attention.

Concentrations of polycyclic aromatic hydrocarbons (PAHs) in liver samples of green turtles Chelonia mydas stranded in the Potiguar Basin, northeastern Brazil

Sea turtles are affected by pollutants worldwide, and the polycyclic aromatic hydrocarbons (PAHs) have been detected in different types of samples and at high levels in some cases. The present study brings concentrations of 37 PAHs in liver samples of 17 green turtles Chelonia mydas stranded in northeastern Brazil [four with cutaneous tumors of fibropapillomatosis (FP), being classified as FP+]. Six PAHs were detected in 100% of the liver samples, and all alkylated PAHs were frequently quantified. High levels of phenanthrene (771.20 and 794.43 ng g^-1 d.w.) and fluorene (1882.36 ng g^-1 d.w.) were found in three females FP- (without FP cutaneous tumors). On the other hand, one green turtle FP+ had the higher level of naphthalene (531.70 ng g^-1 d.w.), compound detected in 82.35 % of the samples. Our study brings additional baseline of organic pollutants in green turtles, improving knowledge on bioaccumulation of these compounds in sea turtles.

The use of an alimentary index to assess anthropogenic debris on green turtles (Chelonia mydas)

Studies on novel methodologies addressed to quantification of anthropogenic marine debris (AMD) types ingested by green turtles (Chelonia mydas) is not common in the scientific literature. To fill this gap, we used the alimentary index (IAi) to quantify and classify AMD ingested by green turtles stranded in the Potiguar Basin, northeastern Brazil. We classified 295 green turtles as juveniles (JUV-I (n = 190) and JUV-II (n = 58)) and adults (ADU (n = 47)). We collected gut contents during necropsy and analyzed them using the IAi. The IAi values were categorized as main (IAi ≥ 0.5), secondary (0.25 ≤ IAi < 0.5), and accessory (IAi < 0.25). The results revealed that transparent soft plastic was an accessory item for the three size groups and the second most frequent item (IAi = 0.23) for JUV-I. Our study brings insights into the application of the IAi to evaluate the amount and types of AMD ingested by green turtles.

Sea Turtles in the Cancer Risk Landscape: A Global Meta-Analysis of Fibropapillomatosis Prevalence and Associated Risk Factors

Several cancer risk factors (exposure to ultraviolet-B, pollution, toxins and pathogens) have been identified for wildlife, to form a “cancer risk landscape.” However, information remains limited on how the spatiotemporal variability of these factors impacts the prevalence of cancer in wildlife. Here, we evaluated the cancer risk landscape at 49 foraging sites of the globally distributed green turtle (Chelonia mydas), a species affected by fibropapillomatosis, by integrating data from a global meta-analysis of 31 publications (1994–2019). Evaluated risk factors included ultraviolet light exposure, eutrophication, toxic phytoplanktonic blooms, sea surface temperature, and the presence of mechanical vectors (parasites and symbiotic species). Prevalence was highest in areas where nutrient concentrations facilitated the emergence of toxic phytoplankton blooms. In contrast, ultraviolet light exposure and the presence of parasitic and/or symbiotic species did not appear to impact disease prevalence. Our results indicate that, to counter outbreaks of fibropapillomatosis, management actions that reduce eutrophication in foraging areas should be implemented.

Evolutionary Comparisons of Chelonid Alphaherpesvirus 5 (ChHV5) Genomes from Fibropapillomatosis-Afflicted Green (Chelonia mydas), Olive Ridley (Lepidochelys olivacea) and Kemp's Ridley (Lepidochelys kempii) Sea Turtles

The spreading global sea turtle fibropapillomatosis (FP) epizootic is threatening some of Earth's ancient reptiles, adding to the plethora of threats faced by these keystone species. Understanding this neoplastic disease and its likely aetiological pathogen, chelonid alphaherpesvirus 5 (ChHV5), is crucial to understand how the disease impacts sea turtle populations and species and the future trajectory of disease incidence. We generated 20 ChHV5 genomes, from three sea turtle species, to better understand the viral variant diversity and gene evolution of this oncogenic virus. We revealed previously underappreciated genetic diversity within this virus (with an average of 2035 single nucleotide polymorphisms (SNPs), 1.54% of the ChHV5 genome) and identified genes under the strongest evolutionary pressure. Furthermore, we investigated the phylogeny of ChHV5 at both genome and gene level, confirming the propensity of the virus to be interspecific, with related variants able to infect multiple sea turtle species. Finally, we revealed unexpected intra-host diversity, with up to 0.15% of the viral genome varying between ChHV5 genomes isolated from different tumours concurrently arising within the same individual. These findings offer important insights into ChHV5 biology and provide genomic resources for this oncogenic virus.

Environmental DNA monitoring of oncogenic viral shedding and genomic profiling of sea turtle fibropapillomatosis reveals unusual viral dynamics

Pathogen-induced cancers account for 15% of human tumors and are a growing concern for endangered wildlife. Fibropapillomatosis is an expanding virally and environmentally co-induced sea turtle tumor epizootic. Chelonid herpesvirus 5 (ChHV5) is implicated as a causative virus, but its transmission method and specific role in oncogenesis and progression is unclear. We applied environmental (e)DNA-based viral monitoring to assess viral shedding as a direct means of transmission, and the relationship between tumor burden, surgical resection and ChHV5 shedding. To elucidate the abundance and transcriptional status of ChHV5 across early, established, regrowth and internal tumors we conducted genomics and transcriptomics. We determined that ChHV5 is shed into the water column, representing a likely transmission route, and revealed novel temporal shedding dynamics and tumor burden correlations. ChHV5 was more abundant in the water column than in marine leeches. We also revealed that ChHV5 is latent in fibropapillomatosis, including early stage, regrowth and internal tumors; higher viral transcription is not indicative of poor patient outcome, and high ChHV5 loads predominantly arise from latent virus. These results expand our knowledge of the cellular and shedding dynamics of ChHV5 and can provide insights into temporal transmission dynamics and viral oncogenesis not readily investigable in tumors of terrestrial species.

Molecular characterization of a marine turtle tumor epizootic, profiling external, internal and postsurgical regrowth tumors

Sea turtle populations are under threat from an epizootic tumor disease (animal epidemic) known as fibropapillomatosis. Fibropapillomatosis continues to spread geographically, with prevalence of the disease also growing at many longer-affected sites globally. However, we do not yet understand the precise environmental, mutational and viral events driving fibropapillomatosis tumor formation and progression.Here we perform transcriptomic and immunohistochemical profiling of five fibropapillomatosis tumor types: external new, established and postsurgical regrowth tumors, and internal lung and kidney tumors. We reveal that internal tumors are molecularly distinct from the more common external tumors. However, they have a small number of conserved potentially therapeutically targetable molecular vulnerabilities in common, such as the MAPK, Wnt, TGFβ and TNF oncogenic signaling pathways. These conserved oncogenic drivers recapitulate remarkably well the core pan-cancer drivers responsible for human cancers. Fibropapillomatosis has been considered benign, but metastatic-related transcriptional signatures are strongly activated in kidney and established external tumors. Tumors in turtles with poor outcomes (died/euthanized) have genes associated with apoptosis and immune function suppressed, with these genes providing putative predictive biomarkers.Together, these results offer an improved understanding of fibropapillomatosis tumorigenesis and provide insights into the origins, inter-tumor relationships, and therapeutic treatment for this wildlife epizootic.

Marine leech parasitism of sea turtles varies across host species, seasons, and the tumor disease fibropapillomatosis

Fibropapillomatosis (FP) is a tumorous disease affecting all species of sea turtles and is associated with the pathogen chelonid alphaherpesvirus 5 (ChHV5). Hypothesized ChHV5 vectors include the marine leeches Ozobranchus branchiatus and O. margoi, but data on their associations with FP and ChHV5 are minimal. To establish relationships between leech parasitism, turtle hosts, and FP, we compared green and loggerhead turtles from the Indian River Lagoon (IRL), Florida, USA, in terms of (1) the presence or absence of ChHV5 within associated leeches, (2) the association between leech parasitism and host FP status, and (3) seasonal variation in leech presence. We identified 55 leeches collected from green turtles as O. branchiatus and 22 leeches collected from loggerhead turtles as O. margoi. Of 77 sequenced leeches, 10 O. branchiatus and 5 O. margoi were ChHV5 positive. ChHV5-positive O. branchiatus trended towards coming from FP-positive hosts. Using 12 yr of turtle capture data from the IRL, we found that leech parasitism was significantly correlated with FP and capture month in green turtles but not in loggerhead turtles. These results suggest that O. branchiatus and O. margoi may differ in their ability to transmit ChHV5 or to encounter and remain on FP-positive hosts. Alternatively, potential immunological differences between green and loggerhead turtles may explain the observed relationships. This study is the first to provide robust statistical evidence of an association between leeches and FP, as well as seasonal fluctuations in leech presence, in green turtles but not in loggerhead turtles.