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

ABSTRACT: 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.

SUBMITTER: Loganathan AL

PROVIDER: S-EPMC8624793 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Fibropapillomatosis (FP) is a debilitating tumor disease affecting all species of sea turtles globally. The most probable etiological agent for FP is the chelonid herpesvirus 5 (ChHV5). A 2015-2016 field survey of the sea turtles at Mabul Island, Sabah, Malaysia, found three green turtles (Chelonia mydas) with FP tumors. However, the presence of ChHV5 was confirmed in 7.8% (9/115) green turtles and was absent (0/16) in the hawksbill (Eretmochelys imbricata) turtles, as determined through molecular approaches. Subsequent to this, we managed to conduct field sampling of sea turtles in November 2019, just prior to the pandemic lockdown. Here, we aim to determine the extent of ChHV5 infection, and whether the virus has spread to other species of sea turtles around Mabul Island after the first reports of ChHV5 and FP. A total of 69 tissue samples were obtained from green (63), hawksbill (5), and olive ridley (Lepidochelys olivacea) (1) turtles in November 2019. We observed only one green turtle that exhibited FP tumors. To determine the presence of ChHV5, viral DNA was isolated from all the tissue samples, and polymerase chain reaction (PCR) analysis targeting three highly conserved regions of the virus, i.e., the capsid protein gene, glycoprotein H gene, and glycoprotein B gene, was performed. Out of 63 green turtles, 27 were positive for the presence of the virus. The prevalence of ChHV5 in the green turtles showed an increase of 42.9% as compared to the previous sampling conducted in 2015-2016. Additionally, for the first time, three out of the five hawksbill turtles, and one olive ridley turtle, were also PCR-positive for the virus. In conclusion, this study reveals that there has been an increase in ChHV5 infection among turtles in Mabul Island over the last 3 years. ChHV5 should be considered a potential threat, and mitigation efforts should be taken to prevent the spread of infection among the endangered sea turtles of Mabul Island and surrounding islands within the Coral Triangle.

Project description: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.

Project description:Fibropapillomatosis is associated with chelonid alphaherpesvirus 5 (ChHV5) and tumor formation in sea turtles. We collected blood samples from 113 green (Chelonia mydas) and 112 loggerhead (Caretta caretta) turtles without fibropapillomatosis, including 46 free-ranging turtles (20 green turtles, 26 loggerheads), captured in Core Sound, North Carolina, and 179 turtles (93 green turtles, 86 loggerheads) in rehabilitative care in North Carolina. Blood samples were analyzed for ChHV5 DNA using quantitative polymerase chain reaction (qPCR), and for antibodies to ChHV5 peptides using an enzyme-linked immunosorbent assay (ELISA). None of the samples from foraging turtles tested positive for ChHV5 by qPCR; ELISA was not used for foraging turtles. Samples from 18/179 (10.1%) rehabilitating turtles tested positive for ChHV5 using qPCR, and 32/56 (57.1%) rehabilitating turtles tested positive for antibodies to ChHV5 using ELISA. Five turtles that tested positive by qPCR or ELISA at admission converted to being undetectable during rehabilitation, and five that initially tested negative converted to being positive. Both sea turtle species were significantly more likely to test positive for ChHV5 using ELISA than with qPCR (p < 0.001). There was no difference in the proportions of green turtles versus loggerheads that tested positive for ChHV5 using qPCR, but loggerheads were significantly more likely than green turtles to test positive for ChHV5 using ELISA. This finding suggests that loggerheads infected with ChHV5 at some point in their life may be more able than green turtles to mount an effective immune response against recrudescent infection, pointing to species-specific genetic differences in the two species' immune response to ChHV5 infection. This is the first study to analyze antibodies to ChHV5 in loggerhead turtles and represents the most complete dataset on ChHV5 DNA detection in sea turtles encountered in the more northern latitudes of their western Atlantic habitat.

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

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