In vitro biology of fibropapilloma-associated turtle herpesvirus and host cells in Hawaiian green turtles (Chelonia mydas)

Evaluation of anthropogenic impacts on marine turtle populations in Lençóis Maranhenses National Park

Currently, one of the most significant threats to marine turtle populations is incidental capture, which can occur on a large scale due to industrial, coastal, or artisanal fishing practices, such as gillnets, fish corrals, longlines, and trawl nets. Other threats exacerbate the situation for these animals, including environmental degradation, global warming, and noise pollution associated with navigation, oil and gas exploration and production, naval sonars, military operations, fishing, and marine seismic research. Our objective was to evaluate and identify anthropogenic impacts on marine turtle populations in the Lençóis Maranhenses National Park. Between 2015 and 2019, systematic monitoring recorded 173 marine turtle strandings, including 164 dead and nine live individuals of E. imbricata, predominantly of C. mydas (46.2 %, n = 80), L. olivacea (38.2 %, n = 66), E. imbricata (5.2 %, n = 9), C. caretta (0.6 %, n = 1), and 9.8 % (n = 17) unidentified. Among the 44 individuals with determined causes of death, 79.5 % (n = 35) were linked to anthropogenic actions, 9 % (n = 4) to natural causes, and 11.3 % (n = 5) to mixed anthropogenic/natural factors. The remaining 129 cases were classified as indeterminate. A significant increase in strandings was observed during the 3D seismic survey period (mean = 34.4 strandings/bimester) compared to periods without seismic activity (mean = 4.8 strandings/bimester). These results underscore that cumulative threats, particularly human-driven pressures, severely impact marine turtle populations. An enhanced understanding of these dynamics is critical for developing targeted conservation strategies at Lençóis Maranhenses National Park. The findings provide actionable insights to mitigate anthropogenic impacts and inform regional management plans.

Preparation of recombinant glycoprotein B (gB) of Chelonid herpesvirus 5 (ChHV5) for antibody production and its application for infection detection in sea turtles

The Chelonid herpesvirus 5 (ChHV5) infection possibly associated to the fibropapillomatosis (FP) disease in sea turtles worldwide remains largely unknown and limited studies have used serological approaches to detection of antibodies against ChHV5 in sea turtles with or without FP. We aimed to develop diagnostic platforms based on the viral glycoprotein B (gB) for ChHV5 infection. In this study, five recombinant sub-fragments of the gB protein were successfully expressed and subsequently served as antigens for both seroprevalence and antibody production. The results indicated that the five expressed proteins harbored antigenicity, shown by the results of using sera from sea turtles that were PCR-positive for ChHV5. Moreover, seropositive sea turtles were significantly associated with FP (p < 0.05). We further used the expressed protein to produce antibodies for immunohistochemical analysis, and found that the in-house-generated sera specifically stained FP lesions while normal epithelium tissues remained negative. Of major importance, the reactivity in the ballooning degeneration area was much stronger than that in other regions of the FP lesion/tumour, thus indicating ChHV5 viral activities. In summary, the developed serological test and specific anti-gB antibodies for IHC analysis could be applied for further understanding of epidemiological distributions of ChHV5 infection in sea turtles, and studies of ChHV5 pathogenesis.

High Occurrence of Chelonid Alphaherpesvirus 5 (ChHV5) in Green Sea Turtles Chelonia mydas with and without Fibropapillomatosis in Feeding Areas of the São Paulo Coast, Brazil

Chelonid alphaherpesvirus 5 (ChHV5) has been consistently associated with fibropapillomatosis (FP), a neoplastic disease that affects sea turtles globally. The DNA of ChHV5 has been detected in cutaneous and noncutaneous tissues (e.g., lung) of green sea turtles Chelonia mydas with (FP+) and without (FP-) clinical signs of FP, indicating a persistent ChHV5 infection. Previously published and custom primer pairs were used to amplify the fragments of ChHV5 unique long (UL) partial genes (UL30 and UL18) through end-point PCR from cutaneous tumors (n = 31), nontumored skin (n = 49), and lungs (n = 26) from FP+ (n = 31) and FP- (n = 18) green sea turtles. The DNA of ChHV5 was detected in cutaneous tumors (80.6%, 25/31), nontumored skin (74.2%, 23/31 FP+; 27.8%, 5/18 FP-), and lung samples (91.7%, 11/12 FP+; 100%, 14/14 FP-). The high occurrence of ChHV5 observed in lung samples from FP- individuals was unexpected (14/14), providing the first evidence of ChHV5 DNA presence in lungs of individuals without FP. Our results also revealed high ChHV5 occurrence among the tested cohort (93.9%, 46/49) and suggested that a large proportion (83.4%, 15/18) of FP- green sea turtles had subclinical ChHV5 infections. Hence, our findings support the hypothesis that ChHV5 requires one or more possibly environmental or immune-related co-factors to induce FP.

First Evidence of Chelonid Herpesvirus 5 (ChHV5) Infection in Green Turtles (Chelonia mydas) from Sabah, Borneo

Fibropapillomatosis (FP) of sea turtles is characterised by cutaneous tumours and is associated with Chelonid herpesvirus 5 (ChHV5), an alphaherpesvirus from the family Herpesviridae. Here, we provide the first evidence of ChHV5-associated FP in endangered Green turtles (Chelonia mydas) from Sabah, which is located at the northern region of Malaysian Borneo. The aims of our study were firstly, to determine the presence of ChHV5 in both tumour exhibiting and tumour-free turtles using molecular techniques and secondly, to determine the phylogeography of ChHV5 in Sabah. We also aim to provide evidence of ChHV5 infection through histopathological examinations. A total of 115 Green turtles were sampled from Mabul Island, Sabah. We observed three Green turtles that exhibited FP tumours and were positive for ChHV5. In addition, six clinically healthy turtles (with no presence of tumours) were also positive for the virus based on Polymerase Chain Reaction of three viral genes (Capsid protein gene UL18, Glycoprotein H gene UL22, and Glycoprotein B gene UL27). The prevalence of the ChHV5 was 5.22% in asymptomatic Green turtles. Epidermal intranuclear inclusions were identified in tumour lesions upon histopathological examination. In addition, phylogenetic analyses of the UL18, UL22, UL27, and UL30 gene sequences showed a worldwide distribution of the ChHV5 strain with no clear distinction based on geographical location suggesting an interoceanic connection and movement of the sea turtles. Thus, the emergence of ChHV5 in Green turtles in the waters of Sabah could indicate a possible threat to sea turtle populations in the future and requires further monitoring of the populations along the Bornean coast.

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.

Genetic Analysis of Chelonid Herpesvirus 5 in Marine Turtles from Baja California Peninsula

The Chelonid herpesvirus 5 (ChHV5) is the primary etiological agent associated with fibropapillomatosis (FP), a neoplastic disease in marine turtles. In this study, we report for the first time ChHV5 in marine turtles and a leech from Baja California Peninsula. Eighty-seven black, olive or loggerhead turtle species, one FP tumor and five leeches were analyzed. The tumor sample from an olive, a skin sample from a black and a leech resulted positive of ChHV5 for conventional PCR. Two viral variants were identified and grouped within the Eastern Pacific phylogenetic group, suggesting a possible flow of the virus in this region.

Differences in Antibody Responses against Chelonid Alphaherpesvirus 5 (ChHV5) Suggest Differences in Virus Biology in ChHV5-Seropositive Green Turtles from Hawaii and ChHV5-Seropositive Green Turtles from Florida

Fibropapillomatosis (FP) is a tumor disease associated with a herpesvirus (chelonid herpesvirus 5 [ChHV5]) that affects mainly green turtles globally. Understanding the epidemiology of FP has been hampered by a lack of robust serological assays to monitor exposure to ChHV5. This is due in part to an inability to efficiently culture the virus in vitro for neutralization assays. Here, we expressed two glycoproteins (FUS4 and FUS8) from ChHV5 using baculovirus. These proteins were immobilized on enzyme-linked immunosorbent assay plates in their native form and assayed for reactivity to two types of antibodies, full-length 7S IgY and 5.7S IgY, which has a truncated Fc region. Turtles from Florida were uniformly seropositive to ChHV5 regardless of tumor status. In contrast, in turtles from Hawaii, we detected strong antibody reactivity mainly in tumored animals, with a lower antibody response being seen in nontumored animals, including those from areas where FP is enzootic. Turtles from Hawaii actively shedding ChHV5 were more seropositive than nonshedders. In trying to account for differences in the serological responses to ChHV5 between green turtles from Hawaii and green turtles from Florida, we rejected the cross-reactivity of antibodies to other herpesviruses, differences in viral epitopes, or differences in procedure as likely explanations. Rather, behavioral or other differences between green turtles from Hawaii and green turtles from Florida might have led to the emergence of biologically different viral strains. While the strains from turtles in Florida apparently spread independently of tumors, the transmission of the Hawaiian subtype relies heavily on tumor formation.IMPORTANCE Fibropapillomatosis (FP) is a tumor disease associated with chelonid herpesvirus 5 (ChHV5) that is an important cause of mortality in threatened green turtles globally. FP is expanding in Florida and the Caribbean but declining in Hawaii. We show that Hawaiian turtles mount antibodies to ChHV5 mainly in response to tumors, which are the only sites of viral replication, whereas tumored and nontumored Floridian turtles are uniformly seropositive. Tumor viruses that depend on tumors for replication and spread are rare, with the only example being the retrovirus causing walleye dermal sarcoma in fish. The Hawaiian strain of ChHV5 may be the first DNA virus with such an unusual life history. Our findings, along with the fundamental differences in the life histories between Floridian turtles and Hawaiian turtles, may partly explain the differential dynamics of FP between the two regions.

Towards the development of standardised sea turtle primary cell cultures for toxicity testing

Chemical contaminants are known to accumulate in marine megafauna globally, but little is known about how this impacts animal health. In vitro assays offer an ethical, reproducible and cost-effective alternative to live animal toxicity testing on large, long-lived or threatened species, such as sea turtles. However, using a cell culture from a single animal raise the question of whether the toxicity observed adequately represents the toxicity in that species. This study examined variation in the cytotoxic response of primary skin fibroblasts established from seven green (Chelonia mydas) and five loggerhead (Caretta caretta) sea turtles. Cell viability using resazurin dye was examined in response to exposure to five contaminants. The variation in cytotoxicity was generally low (within a factor of five) for both independent analyses of the same cell culture, and cell cultures from different individuals. This low within and between cell culture variation indicates that primary sea turtle cell cultures can provide a suitable approach to understanding toxicity in sea turtles. In addition, green and loggerhead turtle cells showed similar toxicity to the compounds tested, indicating that only subtle differences in chemical sensitivity may exist between sea turtle species. This study provides a framework for using species-specific cell cultures in future toxicological studies on sea turtles. Although in vivo studies are the gold standard for toxicological studies and species-specific risk assessments, the development of in vitro tools can provide important information when in vivo studies are not possible or practical. For large, endangered species such as sea turtles that are exposed to, and accumulate, a large number of contaminants, using validated cell cultures may facilitate the rapid assessment of chemical risk to these animals.

Cytotoxicity of organic and inorganic compounds to primary cell cultures established from internal tissues of Chelonia mydas

Chemical contaminants have been found in the tissues of sea turtles from all over the world; however, very little is known about the effects. Recently, in vitro alternatives to live animal testing have been applied to sea turtles due to their ethical and practical benefits. While primary skin fibroblasts have been established for several species of sea turtle, cells from internal organs are lacking, though they may be more relevant due to the well documented accumulation of contaminants within internal tissues. This study established primary cell cultures from the small intestine, heart, liver, ovary and skin of green turtles (Chelonia mydas). Cells were exposed to ten contaminants typically found in sea turtles to examine potential variations in sensitivity among cells established from different organs. Differences between cells established from different animals were also examined, including a comparison of cells established from a turtle with fibropapillomatosis (FP) and healthy turtles. Loggerhead (Caretta caretta) primary skin cells were also included for species comparisons. Significant differences were found between the organ types, with liver and heart being the least sensitive, and skin being the most sensitive. Overall, variation between the organ types was low. Primary skin fibroblasts may be a suitable and representative cell type for in vitro turtle toxicology research, as it is relatively easy to obtain from healthy live animals. Skin cultures provide a more sensitive indication of effect, and could be used as an early warning of the potential effects of chemical contamination. Some species differences were found but no differences were found between cell cultures from an FP turtle and healthy turtles. When EC₅₀ values were compared to accumulation values from the literature, inorganic contaminants, such as Zn, Cd, Cr, Hg, and Cu were identified as posing a potential risk to sea turtle populations around the world.

Molecular evolution of fibropapilloma-associated herpesviruses infecting juvenile green and loggerhead sea turtles

Chelonid Alphaherpesvirus 5 (ChHV5) has long been associated with fibropapillomatosis (FP) tumor disease in marine turtles. Presenting primarily in juvenile animals, FP results in fibromas of the skin, connective tissue, and internal organs, which may indirectly affect fitness by obstructing normal turtle processes. ChHV5 is near-universally present in tumorous tissues taken from affected animals, often at very high concentrations. However, there is also considerable asymptomatic carriage amongst healthy marine turtles, suggesting that asymptomatic hosts play an important role in disease ecology. Currently, there is a paucity of studies investigating variation in viral genetics between diseased and asymptomatic hosts, which could potentially explain why only some ChHV5 infections lead to tumor formation. Here, we generated a database containing DNA from over 400 tissue samples taken from green and loggerhead marine turtles, including multiple tissue types, a twenty year time span, and both diseased and asymptomatic animals. We used two molecular detection techniques, quantitative (q)PCR and nested PCR, to characterize the presence and genetic lineage of ChHV5 in each sample. We found that nested PCR across multiple loci out-performed qPCR and is a more powerful technique for determining infection status. Phylogenetic reconstruction of three viral loci from all ChHV5-positive samples indicated widespread panmixia of viral lineages, with samples taken across decades, species, disease states, and tissues all falling within the same evolutionary lineages. Haplotype networks produced similar results in that viral haplotypes were shared across species, tissue types and disease states with no evidence that viral lineages associated significantly with disease dynamics. Additionally, tests of selection on viral gene trees indicated signals of selection dividing major clades, though this selection did not divide sample categories. Based on these data, neither the presence of ChHV5 infection nor neutral genetic divergence between viral lineages infecting a juvenile marine turtle is sufficient to explain the development of FP within an individual.

Sea turtle fibropapilloma tumors share genomic drivers and therapeutic vulnerabilities with human cancers

Wildlife populations are under intense anthropogenic pressures, with the geographic range of many species shrinking, dramatic reductions in population numbers and undisturbed habitats, and biodiversity loss. It is postulated that we are in the midst of a sixth (Anthropocene) mass extinction event, the first to be induced by human activity. Further, threatening vulnerable species is the increased rate of emerging diseases, another consequence of anthropogenic activities. Innovative approaches are required to help maintain healthy populations until the chronic underlying causes of these issues can be addressed. Fibropapillomatosis in sea turtles is one such wildlife disease. Here, we applied precision-medicine-based approaches to profile fibropapillomatosis tumors to better understand their biology, identify novel therapeutics, and gain insights into viral and environmental triggers for fibropapillomatosis. We show that fibropapillomatosis tumors share genetic vulnerabilities with human cancer types, revealing that they are amenable to treatment with human anti-cancer therapeutics.

David Duffy et al. use a precision-medicine-based approach to study fibropapillomatosis tumors in sea turtles to identify environmental triggers and potential therapeutics. They show that these tumors share genetic similarities with human cancer types, and may be treatable using human anti-cancer therapies.

Concentrations of polycyclic aromatic hydrocarbons in liver samples of juvenile green sea turtles from Brazil: Can these compounds play a role in the development of fibropapillomatosis?

Fibropapillomatosis (FP) poses a significant threat to the conservation of green sea turtles (Chelonia mydas). Polycyclic aromatic hydrocarbons-PAHs are considered mutagenic, carcinogenic and toxic, and can act as cofactor of this disease. In order to evaluate possible differences between green sea turtles with and without FP, we monitored 15 PAHs in liver samples of 44 specimens (24 with FP) captured in Brazil. We detected eight PAHs and quantified phenanthrene in all green sea turtles with FP. Specimens without FP presented lower values than the tumored ones (1.48 ng g^-1 and 17.35 ng g^-1, respectively; p < 0.0001). There were no significant differences between tumored and non-tumored specimens, among studied areas, or Southwest Atlantic Fibropapillomatosis Score. Even though we found higher concentrations in the liver samples of green sea turtles with FP, further studies are necessary to confirm if these pollutants are involved in the pathogenesis of the disease.

Discovery of an Australian Chelonia mydas papillomavirus via green turtle primary cell culture and qPCR

The number of reptilian viruses detected are continuously increasing due to improvements and developments of new diagnostic techniques. In this case we used primary cell culture and qPCR to describe the first Australian Chelonia mydas papillomavirus. Commercial chelonian cell lines are limited to one cell line from a terrestrial turtle (Terrapene Carolina). To establish primary cultures from green turtles (Chelonia mydas), turtle eggs were collected from Heron Island, Queensland, Australia. From day 35 of incubation at 29°, the embryos were harvested to establish primary cultures. The primary cell cultures were grown in Dulbecco's Modified Eagle Medium, 90% and foetal bovine serum, 10%. The cells became uniformly fibroblastic-shaped after 15 passages. The growth rate resembled that of cells originating from other cold-blooded animals and the average doubling time was ∼5 days from the 20th passage. Karyotyping and molecular analysis of mitochondrial DNA D-loop gene were carried out for cell authentication. The primary cell cultures were screened to exclude mycoplasma contamination. Two primary cell lineages were found to be susceptible to Bohle iridovirus. The primary cell cultures were used to screen samples from green turtles foraging along the East Coast of Queensland for the presence of viruses. Homogenates from eight skin tumour samples caused cytopathic effects and were confirmed by qPCR to be infected with papillomavirus.

Genomic evolution, recombination, and inter-strain diversity of chelonid alphaherpesvirus 5 from Florida and Hawaii green sea turtles with fibropapillomatosis

Chelonid alphaherpesvirus 5 (ChHV5) is a herpesvirus associated with fibropapillomatosis (FP) in sea turtles worldwide. Single-locus typing has previously shown differentiation between Atlantic and Pacific strains of this virus, with low variation within each geographic clade. However, a lack of multi-locus genomic sequence data hinders understanding of the rate and mechanisms of ChHV5 evolutionary divergence, as well as how these genomic changes may contribute to differences in disease manifestation. To assess genomic variation in ChHV5 among five Hawaii and three Florida green sea turtles, we used high-throughput short-read sequencing of long-range PCR products amplified from tumor tissue using primers designed from the single available ChHV5 reference genome from a Hawaii green sea turtle. This strategy recovered sequence data from both geographic regions for approximately 75% of the predicted ChHV5 coding sequences. The average nucleotide divergence between geographic populations was 1.5%; most of the substitutions were fixed differences between regions. Protein divergence was generally low (average 0.08%), and ranged between 0 and 5.3%. Several atypical genes originally identified and annotated in the reference genome were confirmed in ChHV5 genomes from both geographic locations. Unambiguous recombination events between geographic regions were identified, and clustering of private alleles suggests the prevalence of recombination in the evolutionary history of ChHV5. This study significantly increased the amount of sequence data available from ChHV5 strains, enabling informed selection of loci for future population genetic and natural history studies, and suggesting the (possibly latent) co-infection of individuals by well-differentiated geographic variants.

In Vitro Replication of Chelonid Herpesvirus 5 in Organotypic Skin Cultures from Hawaiian Green Turtles (Chelonia mydas)

Fibropapillomatosis (FP) is a tumor disease of marine turtles associated with chelonid herpesvirus 5 (ChHV5), which has historically been refractory to growth in tissue culture. Here we show, for the first time, de novo formation of ChHV5-positive intranuclear inclusions in cultured green turtle cells, which is indicative of active lytic replication of the virus. The minimal requirements to achieve lytic replication in cultured cells included (i) either in vitro cultures of ChHV5-positive tumor biopsy specimens (plugs) or organotypic cultures (rafts) consisting of ChHV5-positive turtle fibroblasts in collagen rafts seeded with turtle keratinocytes and (ii) keratinocyte maturation induced by raising raft or biopsy cultures to the air-liquid interface. Virus growth was confirmed by detailed electron microscopic studies that revealed intranuclear sun-shaped capsid factories, tubules, various stages of capsid formation, nuclear export by budding into the perinuclear space, tegument formation, and envelopment to complete de novo virus production. Membrane synthesis was also observed as a sign of active viral replication. Interestingly, cytoplasmic particles became associated with keratin filaments, a feature not seen in conventional monolayer cell cultures, in which most studies of herpesvirus replication have been performed. Our findings draw a rich and realistic picture of ChHV5 replication in cells derived from its natural host and may be crucial not only to better understand ChHV5 circulation but also to eventually complete Koch's postulates for FP. Moreover, the principles described here may serve as a model for culture of other viruses that are resistant to replication in conventional cell culture.IMPORTANCE A major challenge in virology is the study of viruses that cannot be grown in the laboratory. One example is chelonid herpesvirus 5 (ChHV5), which is associated with fibropapillomatosis, a globally distributed, debilitating, and fatal tumor disease of endangered marine turtles. Pathological examination shows that ChHV5 is shed in skin. Here we show that ChHV5 will grow in vitro if we replicate the complex three-dimensional structure of turtle skin. Moreover, lytic virus growth requires a close interplay between fibroblasts and keratinocytes. Finally, the morphogenesis of herpesviral growth in three-dimensional cultures reveals a far richer, and likely more realistic, array of capsid morphologies than that encountered in traditional monolayer cell cultures. Our findings have applications to other viruses, including those of humans.

Challenges in Evaluating the Severity of Fibropapillomatosis: A Proposal for Objective Index and Score System for Green Sea Turtles (Chelonia mydas) in Brazil

Fibropapillomatosis (FP) is a neoplastic disease that affects marine turtles worldwide, especially green sea turtles (Chelonia mydas). FP tumors can develop on the body surface of marine turtles and also internally in the oral cavity and viscera. Depending on their quantity, size and anatomical distribution, these tumors can interfere with hydrodynamics and the ability to feed, hence scoring systems have been proposed in an attempt to quantify the clinical manifestation of FP. In order to establish a new scoring system adapted to geographic regions, we examined 214 juvenile green sea turtles with FP caught or rescued at Brazilian feeding areas, counted their 7466 tumors and classified them in relation to their size and anatomical distribution. The patterns in quantity, size and distribution of tumors revealed interesting aspects in the clinical manifestation of FP in specimens studied in Brazil, and that FP scoring systems developed for other areas might not perform adequately when applied to sea turtles on the Southwest Atlantic Ocean. We therefore propose a novel method to evaluate the clinical manifestation of FP: fibropapillomatosis index (FPI) that provides the Southwest Atlantic fibropapillomatosis score (FPSSWA). In combination, these indexing and scoring systems allow for a more objective, rapid and detailed evaluation of the severity of FP in green sea turtles. While primarily designed for the clinical manifestation of FP currently witnessed in our dataset, this index and the score system can be adapted for other areas and compare the characteristics of the disease across regions. In conclusion, scoring systems to classify the severity of FP can assist our understanding on the environmental factors that modulate its development and its impacts on the individual and population health of green sea turtles.

Further evidence of Chelonid herpesvirus 5 (ChHV5) latency: high levels of ChHV5 DNA detected in clinically healthy marine turtles

The Chelonid herpesvirus 5 (ChHV5) has been consistently associated with fibropapillomatosis (FP), a transmissible neoplastic disease of marine turtles. Whether ChHV5 plays a causal role remains debated, partly because while FP tumours have been clearly documented to contain high concentrations of ChHV5 DNA, recent PCR-based studies have demonstrated that large proportions of asymptomatic marine turtles are also carriers of ChHV5. We used a real-time PCR assay to quantify the levels of ChHV5 Glycoprotein B (gB) DNA in both tumour and non-tumour skin tissues, from clinically affected and healthy turtles drawn from distant ocean basins across four species. In agreement with previous studies, higher ratios of viral to host DNA were consistently observed in tumour versus non-tumour tissues in turtles with FP. Unexpectedly however, the levels of ChHV5 gB DNA in clinically healthy turtles were significantly higher than in non-tumour tissues from FP positive turtles. Thus, a large proportion of clinically healthy sea turtle populations worldwide across species carry ChHV5 gB DNA presumably through persistent latent infections. ChHV5 appears to be ubiquitous regardless of the animals’ clinical conditions. Hence, these results support the theory that ChHV5 is a near ubiquitous virus with latency characteristics requiring co-factors, possibly environmental or immune related, to induce FP.

A review of fibropapillomatosis in Green turtles (Chelonia mydas)

Despite being identified in 1938, many aspects of the pathogenesis and epidemiology of fibropapillomatosis (FP) in marine turtles are yet to be fully uncovered. Current knowledge suggests that FP is an emerging infectious disease, with the prevalence varying both spatially and temporally, even between localities in close proximity to each other. A high prevalence of FP in marine turtles has been correlated with residency in areas of reduced water quality, indicating that there is an environmental influence on disease presentation. Chelonid herpesvirus 5 (ChHV5) has been identified as the likely aetiological agent of FP. The current taxonomic position of ChHV5 is in the family Herpesviridae, subfamily Alphaherpesvirinae, genus Scutavirus. Molecular differentiation of strains has revealed that a viral variant is typically present at specific locations, even within sympatric species of marine turtles, indicating that the disease FP originates regionally. There is uncertainty surrounding the exact path of transmission and the conditions that facilitate lesion development, although recent research has identified atypical genes within the genome of ChHV5 that may play a role in pathogenesis. This review discusses emerging areas where researchers might focus and theories behind the emergence of FP globally since the 1980s, which appear to be a multi-factorial interplay between the virus, the host and environmental factors influencing disease expression.

Case descriptions of fibropapillomatosis in rehabilitating loggerhead sea turtles Caretta caretta in the southeastern USA

Fibropapillomatosis (FP) is a debilitating neoplastic disease that affects all species of hard-shelled sea turtles, including loggerhead turtles Caretta caretta. FP can represent an important clinical concern in rehabilitating turtles, since managing these infectious lesions often requires special husbandry provisions including quarantine, and FP may affect clinical progression, extend rehabilitation duration, and complicate prognoses. Here we describe cases of rehabilitating loggerhead turtles with FP (designated FP+). Medical records of FP+ loggerhead cases from 3 sea turtle rehabilitation facilities in the southeastern USA were reviewed. Between 2001 and 2014, FP was observed in 8 of 818 rehabilitating loggerhead turtles (0.98% overall prevalence in admitted patients). FP+ loggerhead size classes represented were large juvenile (straight carapace length, SCL: 58.1-80 cm; n=7) and adult (SCL>87 cm; n=1). Three turtles presented with FP, and 5 developed tumors during rehabilitation within a range of 45 to 319 d. Sites of new tumor growth included the eyes, sites of trauma, neck, and glottis. FP+ turtles were scored as mildly (3/8), moderately (4/8), or heavily (1/8) afflicted. The mean total time in rehabilitation was 476±355 d (SD) (range: 52-1159 d). Six turtles were released without visible evidence of FP, 1 turtle was released with mild FP, and 1 turtle with internal FP was euthanized. Clinical decision-making for FP+ loggerhead patients can be aided by such information as time to tumor development, anatomic locations to monitor for new tumor growth, husbandry considerations, diagnostic and treatment options, and comparisons to FP in rehabilitating green turtles Chelonia mydas.

Establishment, characterization, and toxicological application of loggerhead sea turtle (Caretta caretta) primary skin fibroblast cell cultures

Pollution is a well-known threat to sea turtles but its impact is poorly understood. In vitro toxicity testing presents a promising avenue to assess and monitor the effects of environmental pollutants in these animals within the legal constraints of their endangered status. Reptilian cell cultures are rare and, in sea turtles, largely derived from animals affected by tumors. Here we describe the full characterization of primary skin fibroblast cell cultures derived from biopsies of multiple healthy loggerhead sea turtles (Caretta caretta), and the subsequent optimization of traditional in vitro toxicity assays to reptilian cells. Characterization included validating fibroblast cells by morphology and immunocytochemistry, and optimizing culture conditions by use of growth curve assays with a fractional factorial experimental design. Two cell viability assays, MTT and lactate dehydrogenase (LDH), and an assay measuring cytochrome P4501A (CYP1A) expression by quantitative PCR were optimized in the characterized cells. MTT and LDH assays confirmed cytotoxicity of perfluorooctanoic acid at 500 μM following 72 and 96 h exposures while CYP1A5 induction was detected after 72 h exposure to 0.1-10 μM benzo[a]pyrene. This research demonstrates the validity of in vitro toxicity testing in sea turtles and highlights the need to optimize mammalian assays to reptilian cells.

Dynamics of Virus Shedding and In Situ Confirmation of Chelonid Herpesvirus 5 in Hawaiian Green Turtles With Fibropapillomatosis

Cancers in humans and animals can be caused by viruses, but virus-induced tumors are considered to be poor sites for replication of intact virions (lytic replication). Fibropapillomatosis (FP) is a neoplastic disease associated with a herpesvirus, chelonid herpesvirus 5 (ChHV5), that affects green turtles globally. ChHV5 probably replicates in epidermal cells of tumors, because epidermal intranuclear inclusions (EIIs) contain herpesvirus-like particles. However, although EIIs are a sign of herpesvirus replication, they have not yet been firmly linked to ChHV5. Moreover, the dynamics of viral shedding in turtles are unknown, and there are no serological reagents to confirm actual presence of the specific ChHV5 virus in tissues. The investigators analyzed 381 FP tumors for the presence of EIIs and found that overall, about 35% of green turtles had lytic replication in skin tumors with 7% of tumors showing lytic replication. A few (11%) turtles accounted for more than 30% cases having lytic viral replication, and lytic replication was more likely in smaller tumors. To confirm that turtles were actively replicating ChHV5, a prerequisite for shedding, the investigators used antiserum raised against F-VP26, a predicted capsid protein of ChHV5 that localizes to the host cell nucleus during viral replication. This antiserum revealed F-VP26 in EIIs of tumors, thus confirming the presence of replicating ChHV5. In this light, it is proposed that unlike other virus-induced neoplastic diseases, FP is a disease that may depend on superspreaders, a few highly infectious individuals growing numerous small tumors permissive to viral production, for transmission of ChHV5.

Factors influencing survivorship of rehabilitating green sea turtles (Chelonia mydas) with fibropapillomatosis

Marine turtle fibropapillomatosis (FP) is a debilitating, infectious neoplastic disease that has reached epizootic proportions in several tropical and subtropical populations of green turtles (Chelonia mydas). FP represents an important health concern in sea turtle rehabilitation facilities. The objectives of this study were to describe the observed epidemiology, biology, and survival rates of turtles affected by FP (FP+ turtles) in a rehabilitation environment; to evaluate clinical parameters as predictors of survival in affected rehabilitating turtles; and to provide information about case progression scenarios and potential outcomes for FP+ sea turtle patients. A retrospective case series analysis was performed using the medical records of the Georgia Sea Turtle Center (GSTC), Jekyll Island, Georgia, USA, during 2009-2013. Information evaluated included signalment, morphometrics, presenting complaint, time to FP onset, tumor score (0-3), co-morbid conditions, diagnostic test results, therapeutic interventions, and case outcomes. Overall, FP was present in 27/362 (7.5%) of all sea turtles admitted to the GSTC for rehabilitation, either upon admittance or during their rehabilitation. Of these, 25 were green and 2 were Kemp's ridley turtles. Of 10 turtles that had only plaque-like FP lesions, 60% had natural tumor regression, all were released, and they were significantly more likely to survive than those with classic FP (P = 0.02 [0.27-0.75, 95% CI]). Turtles without ocular FP were eight times more likely to survive than those with ocular FP (odds ratio = 8.75, P = 0.032 [1.21-63.43, 95% CI]). Laser-mediated tumor removal surgery is the treatment of choice for FP+ patients at the GSTC; number of surgeries was not significantly related to case outcome.

Global distribution of Chelonid fibropapilloma-associated herpesvirus among clinically healthy sea turtles

Background

Fibropapillomatosis (FP) is a neoplastic disease characterized by cutaneous tumours that has been documented to infect all sea turtle species. Chelonid fibropapilloma-associated herpesvirus (CFPHV) is believed to be the aetiological agent of FP, based principally on consistent PCR-based detection of herpesvirus DNA sequences from FP tumours. We used a recently described PCR-based assay that targets 3 conserved CFPHV genes, to survey 208 green turtles (Chelonia mydas). This included both FP tumour exhibiting and clinically healthy individuals. An additional 129 globally distributed clinically healthy individual sea turtles; representing four other species were also screened.

Results

CFPHV DNA sequences were obtained from 37/37 (100%) FP exhibiting green turtles, and 45/300 (15%) clinically healthy animals spanning all five species. Although the frequency of infected individuals per turtle population varied considerably, most global populations contained at least one CFPHV positive individual, with the exception of various turtle species from the Arabian Gulf, Northern Indian Ocean and Puerto Rico.

Haplotype analysis of the different gene markers clustered the CFPHV DNA sequences for two of the markers (UL18 and UL22) in turtles from Turks and Caicos separate to all others, regardless of host species or geographic origin.

Conclusion

Presence of CFPHV DNA within globally distributed samples for all five species of sea turtle was confirmed. While 100% of the FP exhibiting green turtles yielded CFPHV sequences, surprisingly, so did 15% of the clinically healthy turtles. We hypothesize that turtle populations with zero (0%) CFPHV frequency may be attributed to possible environmental differences, diet and/or genetic resistance in these individuals. Our results provide first data on the prevalence of CFPHV among seemingly healthy turtles; a factor that may not be directly correlated to the disease incidence, but may suggest of a long-term co-evolutionary latent infection interaction between CFPHV and its turtle-host across species. Finally, computational analysis of amino acid variants within the Turks and Caicos samples suggest potential functional importance in a substitution for marker UL18 that encodes the major capsid protein gene, which potentially could explain differences in pathogenicity. Nevertheless, such a theory remains to be validated by further research.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-014-0206-z) contains supplementary material, which is available to authorized users.

Fibropapillomatosis in green turtles Chelonia mydas in Brazil: characteristics of tumors and virus

Fibropapillomatosis (FP) is a benign neoplasia that affects physiological functions of sea turtles and may lead to death. High prevalence of FP in sea turtle populations has prompted several research groups to study the disease and the associated herpesvirus, chelonid herpesvirus 5 (ChHV5). The present study detected and quantified ChHV5 in 153 fibropapilloma samples collected from green turtles Chelonia mydas on the Brazilian coast between 2009 and 2010 to characterize the relationship between viral load and tumor characteristics. Of the tumor samples collected, 73 and 87% were positive for ChHV5 in conventional PCR and real-time PCR, respectively, and viral loads ranged between 1 and 118.62 copies cell⁻¹. Thirty-three percent of turtles were mildly, 28% were moderately and 39% were severely affected with FP. Skin samples were used as negative control. High viral loads correlated positively with increasing FP severity in turtles sampled on the Brazilian coast and with samples from turtles found dead in the states of São Paulo and Bahia. Six viral variants were detected in tumor samples, 4 of which were similar to the Atlantic phylogenetic group. Two variants were similar to the western Atlantic/eastern Caribbean phylogenetic group. Co-infection in turtles with more than one variant was observed in the states of São Paulo and Bahia.

Validation of a sensitive PCR assay for the detection of Chelonid fibropapilloma-associated herpesvirus in latent turtle infections

The Chelonid fibropapilloma-associated herpesvirus (CFPHV) is hypothesized to be the causative agent of fibropapillomatosis, a neoplastic disease in sea turtles, given its consistent detection by PCR in fibropapilloma tumours. CFPHV has also been detected recently by PCR in tissue samples from clinically healthy (non exhibiting fibropapilloma tumours) turtles, thus representing presumably latent infections of the pathogen. Given that template copy numbers of viruses in latent infections can be very low, extremely sensitive PCR assays are needed to optimize detection efficiency. In this study, efficiency of several PCR assays designed for CFPHV detection is explored and compared to a method published previously. The results show that adoption of a triplet set of singleplex PCR assays outperforms other methods, with an approximately 3-fold increase in detection success in comparison to the standard assay. Thus, a new assay for the detection of CFPHV DNA markers is presented, and adoption of its methodology is recommended in future CFPHV screens among sea turtles.

Hematological and histopathological evaluation of wildlife green turtles (Chelonia mydas) with and without fibropapilloma from the north coast of São Paulo State, Brazil

Blood profiles were determined in 47 juvenile green turtles, Chelonia mydas, from São Paulo northern coast, Brazil. Twenty-nine were affected by fibropapillomas and 18 were tumor free. Complete gross and histopathologic examinations of the fibropapillo were performed in 21 green turtles. Biometrical data, size, location and amount of tumors were recorded. The papillomas varied in morphology, location, size, color and texture. We found hyperplastic stroma, rich in blood vessels and connective tissue with increase in thickness of the dermis. The tumors w0ere classified as papillomas or fibropapillomas according to their epithelial and/or stromal proliferation. The lowest Mean Corpuscular Hemoglobin (HCM) values were observed in affected turtles.

A novel investigation of a blister-like syndrome in aquarium Echinopora lamellosa

This study investigates potential causes of a novel blister-like syndrome in the plating coral Echinopora lamellosa. Visual inspections of this novel coral syndrome showed no obvious signs of macroparasites and the blisters themselves manifested as fluid-filled sacs on the surface of the coral, which rose from the coenosarc between the coral polyps. Histological analysis of the blisters showed that there was no associated necrosis with the epidermal or gastrodermal tissues. The only difference between blistered areas and apparently healthy tissues was the presence of proliferated growth (possible mucosal cell hyperplasia) directly at the blister interface (area between where the edge of the blister joined apparently healthy tissue). No bacterial aggregates were identified in any histological samples, nor any sign of tissue necrosis identified. We conclude, that the blister formations are not apparently caused by a specific microbial infection, but instead may be the result of irritation following growth anomalies of the epidermis. However, future work should be conducted to search for other potential casual agents, including viruses.

Rana grylio virus (RGV) envelope protein 2L: subcellular localization and essential roles in virus infectivity revealed by conditional lethal mutant

Rana grylio virus (RGV) is a pathogenic iridovirus that has resulted in high mortality in cultured frog. Here, an envelope protein gene, 2L, was identified from RGV and its possible role in virus infection was investigated. Database searches found that RGV 2L had homologues in all sequenced iridoviruses and is a core gene of iridoviruses. Western blotting detection of purified RGV virions confirmed that 2L protein was associated with virion membrane. Fluorescence localization revealed that 2L protein co-localized with viral factories in RGV infected cells. In co-transfected cells, 2L protein co-localized with two other viral envelope proteins, 22R and 53R. However, 2L protein did not co-localize with the major capsid protein of RGV in co-transfected cells. Meanwhile, fluorescence observation showed that 2L protein co-localized with endoplasmic reticulum, but did not co-localize with mitochondria and Golgi apparatus. Moreover, a conditional lethal mutant virus containing the lac repressor/operator system was constructed to investigate the role of RGV 2L in virus infection. The ability to form plaques and the virus titres were strongly reduced when expression of 2L was repressed. Therefore, the current data showed that 2L protein is essential for virus infection. Our study is the first report, to our knowledge, of co-localization between envelope proteins in iridovirus and provides new insights into the understanding of envelope proteins in iridovirus.

Presence of chelonid fibropapilloma-associated herpesvirus in tumored and non-tumored green turtles, as detected by polymerase chain reaction, in endemic and non-endemic aggregations, Puerto Rico

Fibropapillomatosis (FP), a transmissible neoplastic disease of marine turtles characterized by a likely herpesviral primary etiology, has emerged as an important disease in green sea turtles (Chelonia mydas) over the past three decades. The objectives of this study were to determine the suitability of three different chelonid fibropapilloma-associated herpesvirus (CFPHV) gene targets in polymerase chain reaction (PCR) assays of affected tissues; to explore the presence of CFPHV in non-affected skin from turtles with and without tumors; and to better understand tissue localization of the CFPHV genome in a tumor-free turtle by evaluating CFPHV presence in microanatomic tissue sites. Two aggregations of green sea turtles (Chelonia mydas) in Puerto Rico were evaluated, with six sampling intervals over the three-year period 2004–2007. Primary and nested PCR for three different herpesviral gene targets- DNA polymerase, capsid maturation protease, and membrane glycoprotein B- were performed on 201 skin biopsies taken from 126 turtles with and without external tumors. Laser capture microdissection and nested PCR were used to identify tissue localizations of CFPHV in skin from a normal turtle. Of the turtles sampled in Manglar Bay, 30.5% had tumors; at the relatively more pristine Culebrita, 5.3% of turtles sampled had tumors. All three PCR primer combinations successfully amplified CFPHV from tumors, and from normal skin of both tumored and tumor-free turtles. Via nested PCR, the polymerase gene target proved superior to the other two gene targets in the positive detection of CFPHV DNA. CFPHV infection may be common relative to disease incidence, supporting the idea that extrinsic and/or host factors could play a transforming role in tumor expression. Laser capture microdissection revealed CFPHV in skin from a tumor-free turtle, harbored in both epidermal and dermal tissues. Identification of CFPHV harbored in a non-epidermal site (dermis) of a tumor-free turtle indicates that virus is latent in a non-tumored host.

The genome of Chelonid herpesvirus 5 harbors atypical genes

The Chelonid fibropapilloma-associated herpesvirus (CFPHV; ChHV5) is believed to be the causative agent of fibropapillomatosis (FP), a neoplastic disease of marine turtles. While clinical signs and pathology of FP are well known, research on ChHV5 has been impeded because no cell culture system for its propagation exists. We have cloned a BAC containing ChHV5 in pTARBAC2.1 and determined its nucleotide sequence. Accordingly, ChHV5 has a type D genome and its predominant gene order is typical for the varicellovirus genus within the alphaherpesvirinae. However, at least four genes that are atypical for an alphaherpesvirus genome were also detected, i.e. two members of the C-type lectin-like domain superfamily (F-lec1, F-lec2), an orthologue to the mouse cytomegalovirus M04 (F-M04) and a viral sialyltransferase (F-sial). Four lines of evidence suggest that these atypical genes are truly part of the ChHV5 genome: (1) the pTARBAC insertion interrupted the UL52 ORF, leaving parts of the gene to either side of the insertion and suggesting that an intact molecule had been cloned. (2) Using FP-associated UL52 (F-UL52) as an anchor and the BAC-derived sequences as a means to generate primers, overlapping PCR was performed with tumor-derived DNA as template, which confirmed the presence of the same stretch of “atypical” DNA in independent FP cases. (3) Pyrosequencing of DNA from independent tumors did not reveal previously undetected viral sequences, suggesting that no apparent loss of viral sequence had happened due to the cloning strategy. (4) The simultaneous presence of previously known ChHV5 sequences and F-sial as well as F-M04 sequences was also confirmed in geographically distinct Australian cases of FP. Finally, transcripts of F-sial and F-M04 but not transcripts of lytic viral genes were detected in tumors from Hawaiian FP-cases. Therefore, we suggest that F-sial and F-M04 may play a role in FP pathogenesis.

Health surveillance of stranded green turtles in southern Queensland, Australia (2006-2009): an epidemiological analysis of causes of disease and mortality

Causes of disease and mortality in marine turtles are frequently based on opportunistic investigations producing results that may not contribute to knowledge on how to protect their survival rate. Over a 4-year period (2006-2009), the major causes of stranding and morbidity in 100 green turtles (Chelonia mydas) from southern Queensland on the east coast of Australia were determined by comprehensive postmortem examination. Lesions were characterized for analysis using descriptive and probability statistics. Spirorchiid parasitism was found to be the most frequently occurring cause of mortality (41.8%), followed by gastrointestinal impaction (11.8%), microbiological infectious diseases (5.2%), and trauma (5.2%). Spirorchiid parasitism with associated inflammation (75%) was the most frequently occurring disease, followed by gastrointestinal impaction (5.1%). All other diseases were observed at a low prevalence. Assessment of the likelihood of disease being influenced by risk factors (season, maturity, and gender) showed that: (i) there were more observed cases of spirorchiid infection in summer when compared with the other seasons (P = 0.029); (ii) immature turtles had more severe spirorchiid parasite infections than mature turtles (P = 0.032); and (iii) respiratory disorders were more likely (P = 0.01) in summer and autumn than winter or spring. Number of observed cases and severity of spirorchiid lesions were highest in the brain compared with other histologically examined organ systems (all P > 0.1). Further investigation is required to build on these findings, aid management decisions, and determine the significance of these diseases for green turtle survivorship in Queensland.

Corneal fibropapillomatosis in green sea turtles (Chelonia mydas) in Australia

Chelonid corneal fibropapillomatosis has not previously been recorded in Australian waters. During 2008, 724 green sea turtles (Chelonia mydas) were examined in Queensland, Australia at two sites, Moreton Bay (n=155) and Shoalwater Bay (n=569), during annual monitoring. In the same calendar year, 63 turtles were submitted from various sites in southern Queensland for post-mortem examination at the University of Queensland. Four of the 787 animals (0.5%) were found to have corneal fibropapillomas of varying size, with similar gross and microscopical features to those reported in other parts of the world. Two animals with corneal fibropapillomas also had cutaneous fibropapillomas. Clinical assessment indicated that these lesions had detrimental effects on the vision of the turtles and therefore their potential ability to source food, avoid predators and interact with conspecifics. Importantly, these findings represent an emergence of this manifestation of fibropapillomatosis in green sea turtle populations in the southern Pacific Ocean.