Amplification and analysis of DNA flanking known sequences of a novel herpesvirus from green turtles with fibropapilloma Brief report

Genotype data not consistent with clonal transmission of sea turtle fibropapillomatosis or goldfish schwannoma

Recent discoveries of transmissible cancers in multiple bivalve species suggest that direct transmission of cancer cells within species may be more common than previously thought, particularly in aquatic environments. Fibropapillomatosis occurs with high prevalence in green sea turtles ( Chelonia mydas) and the geographic range of disease has increased since fibropapillomatosis was first reported in this species. Widespread incidence of schwannomas, benign tumours of Schwann cell origin, reported in aquarium-bred goldfish (Carassius auratus), suggest an infectious aetiology. We investigated the hypothesis that cancers in these species arise by clonal transmission of cancer cells. Through analysis of polymorphic microsatellite alleles, we demonstrate concordance of host and tumour genotypes in diseased animals. These results imply that the tumours examined arose from independent oncogenic transformation of host tissue and were not clonally transmitted. Further, failure to experimentally transmit goldfish schwannoma via water exposure or inoculation suggest that this disease is unlikely to have an infectious aetiology.

The Concurrent Detection of Chelonid Alphaherpesvirus 5 and Chelonia mydas Papillomavirus 1 in Tumoured and Non-Tumoured Green Turtles

Simple Summary

Characterised by benign tumours, fibropapillomatosis is a debilitating disease that predominantly afflicts the endangered green turtle (Chelonia mydas). A growing body of evidence has associated these tumours with a herpesvirus. However, a recent study detected both herpesvirus and papillomavirus in these tumours. This result challenged the idea that the herpesvirus is the sole virus associated with this disease. The present study aimed to better understand the co-occurrence of these viruses in turtles with fibropapillomatosis (in both tumour samples and non-tumoured skin samples), in addition to samples from non-tumoured turtles. Both viruses were detected in all sample types, with the 43.5% of tumours containing both herpesvirus and papillomavirus. Tumour samples were found to contain the most herpesvirus while the highest amount of papillomavirus was detected in non-tumoured skin from turtles with tumours. Collectively, these results pivot the way we think about this disease; as an infectious disease where two separate viruses may be at play.

Abstract

Characterised by benign tumours, fibropapillomatosis (FP) is a debilitating disease that predominantly afflicts the endangered green turtle (Chelonia mydas). A growing body of histological and molecular evidence has associated FP tumours with Chelonid alphaherpesvirus 5 (ChHV5). However, a recent study which detected both ChHV5 and Chelonia mydas papillomavirus 1 (CmPV1) DNA in FP tumour tissues has challenged this hypothesis. The present study aimed to establish a probe-based qPCR to assess the wider prevalence of CmPV1 and co-occurrence with ChHV5 in 275 marine turtles foraging in waters adjacent to the east coast of Queensland, Australia: three categories: Group A (FP tumours), Group B (non-tumoured skin from FP turtles) and Group C (non-tumoured skin from turtles without FP). Concurrent detection of ChHV5 and CmPV1 DNA is reported for all three categories, where Group A had the highest rate (43.5%). ChHV5 viral loads in Group A were significantly higher than loads seen in Group B and C. This was not the case for CmPV1 where the loads in Group B were highest, followed by Group A. However, the mean CmPV1 load for Group A samples was not significantly different to the mean load reported from Group B or C samples. Collectively, these results pivot the way we think about FP; as an infectious disease where two separate viruses may be at play.

Molecular evidence for horizontal transmission of chelonid alphaherpesvirus 5 at green turtle (Chelonia mydas) foraging grounds in Queensland, Australia

Fibropapillomatosis (FP) is a marine turtle disease recognised by benign tumours on the skin, eyes, shell, oral cavity and/or viscera. Despite being a globally distributed disease that affects an endangered species, research on FP and its likely causative agent chelonid alphaherpesvirus 5 (ChHV5) in Australia is limited. Here we present improved molecular assays developed for detection of ChHV5, in combination with a robust molecular and phylogenetic analysis of ChHV5 variants. This approach utilised a multi-gene assay to detect ChHV5 in all FP tumors sampled from 62 marine turtles found at six foraging grounds along the Great Barrier Reef. Six distinct variants of ChHV5 were identified and the distribution of these variants was associated with host foraging ground. Conversely, no association between host genetic origin and ChHV5 viral variant was found. Together this evidence supports the hypothesis that marine turtles undergo horizontal transmission of ChHV5 at foraging grounds and are unlikely to be contracting the disease at rookeries, either during mating or vertically from parent to offspring.

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.

Herpesvirus in a captive Australian Krefft's river turtle (Emydura macquarii krefftii)

CASE REPORT

A mature, captive Krefft's river turtle (Emydura macquarii krefftii) was presented with severe proliferative and ulcerative lesions of the skin and shell. The areas were biopsied and histopathological examination demonstrated orthokeratotic hyperkeratosis with keratinocytes containing eosinophilic intranuclear inclusions. Molecular diagnostics confirmed the presence of a herpesvirus in the affected tissues.

CONCLUSION

This is the first recorded case of herpesvirus infection in an Australian freshwater turtle species.

[T-DNA integration patterns in transgenic plants mediated by Agrobacterium tumefaciens]

The genetic transformation mediated by Agrobacterium tumefaciens has been widely applied to research of transgenic plants. As the vector of the exotic genes, the integration patterns of T-DNA fragments affects not only transformation efficiency and stability, but also expression properties of the transgenes. This review summaries the two major patterns and the rules of T-DNA integration in Agrobacterim-mediated transformation, rules of T-DNA mediated by Agrobacterium tumefaciens, as well as research tools for flanking sequence amplification. It is attempted to provide references for researches on transformation and T-DNA integration mutation mediated by Agrobacterium tumefaciens.

Viruses in reptiles

The etiology of reptilian viral diseases can be attributed to a wide range of viruses occurring across different genera and families. Thirty to forty years ago, studies of viruses in reptiles focused mainly on the zoonotic potential of arboviruses in reptiles and much effort went into surveys and challenge trials of a range of reptiles with eastern and western equine encephalitis as well as Japanese encephalitis viruses. In the past decade, outbreaks of infection with West Nile virus in human populations and in farmed alligators in the USA has seen the research emphasis placed on the issue of reptiles, particularly crocodiles and alligators, being susceptible to, and reservoirs for, this serious zoonotic disease. Although there are many recognised reptilian viruses, the evidence for those being primary pathogens is relatively limited. Transmission studies establishing pathogenicity and cofactors are likewise scarce, possibly due to the relatively low commercial importance of reptiles, difficulties with the availability of animals and permits for statistically sound experiments, difficulties with housing of reptiles in an experimental setting or the inability to propagate some viruses in cell culture to sufficient titres for transmission studies. Viruses as causes of direct loss of threatened species, such as the chelonid fibropapilloma associated herpesvirus and ranaviruses in farmed and wild tortoises and turtles, have re-focused attention back to the characterisation of the viruses as well as diagnosis and pathogenesis in the host itself.

1. Introduction

2. Methods for working with reptilian viruses

3. Reptilian viruses described by virus families

3.1. Herpesviridae

3.2. Iridoviridae

3.2.1 Ranavirus

3.2.2 Erythrocytic virus

3.2.3 Iridovirus

3.3. Poxviridae

3.4. Adenoviridae

3.5. Papillomaviridae

3.6. Parvoviridae

3.7. Reoviridae

3.8. Retroviridae and inclusion body disease of Boid snakes

3.9. Arboviruses

3.9.1. Flaviviridae

3.9.2. Togaviridae

3.10. Caliciviridae

3.11. Picornaviridae

3.12. Paramyxoviridae

4. Summary

5. Acknowledgements

6. Competing interests

7. References

Wildlife cancer: a conservation perspective

Until recently, cancer in wildlife was not considered to be a conservation concern. However, with the identification of Tasmanian devil facial tumour disease, sea turtle fibropapillomatosis and sea lion genital carcinoma, it has become apparent that neoplasia can be highly prevalent and have considerable effects on some species. It is also clear that anthropogenic activities contribute to the development of neoplasia in wildlife species, such as beluga whales and bottom-dwelling fish, making them sensitive sentinels of disturbed environments.

Localization of fibropapilloma-associated turtle herpesvirus in green turtles (Chelonia mydas) by in-situ hybridization

Fibropapilloma-associated turtle herpesvirus (FPTHV) is the presumed aetiological agent of sea turtle fibropapillomatosis (FP). Intralesional DNA and RNA of the virus have been detected by polymerase chain reaction (PCR) and reverse transcriptase-PCR (RT-PCR), respectively, but the exact location and distribution of the virus within the tumours have not been addressed. In this study, in-situ hybridization (ISH) was used to investigate viral transcriptional activity and localization of FPTHV. Twenty-five tumours were obtained from the skin or conjunctiva of 105 green turtles (Chelonia mydas) examined on two islands in Puerto Rico (Culebra and Culebrita). These lesions comprised 19 fibropapillomas and six fibromas. FPTHV mRNA transcripts were detected by ISH in three fibropapillomas, with positive reactions confined to the nuclei of clusters of epithelial cells. Viral DNA was detected by riboprobe ISH combined with denaturation in 14 tumours, including both fibropapillomas and fibromas. Signals were confined to the nuclei of acanthotic epithelial cells and were not seen in the subepithelial fibrous areas of the tumours. These results suggest that FPTHV is present in epithelial cells and transcriptionally active in fibropapillomas.

Viruses of lower vertebrates

Viruses of lower vertebrates recently became a field of interest to the public due to increasing epizootics and economic losses of poikilothermic animals. These were reported worldwide from both wildlife and collections of aquatic poikilothermic animals. Several RNA and DNA viruses infecting fish, amphibians and reptiles have been studied intensively during the last 20 years. Many of these viruses induce diseases resulting in important economic losses of lower vertebrates, especially in fish aquaculture. In addition, some of the DNA viruses seem to be emerging pathogens involved in the worldwide decline in wildlife. Irido-, herpes- and polyomavirus infections may be involved in the reduction in the numbers of endangered amphibian and reptile species. In this context the knowledge of several important RNA viruses such as orthomyxo-, paramyxo-, rhabdo-, retro-, corona-, calici-, toga-, picorna-, noda-, reo- and birnaviruses, and DNA viruses such as parvo-, irido-, herpes-, adeno-, polyoma- and poxviruses, is described in this review.