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fibropapillomatosis of sea turtles

Pictures Top of page Picture Title Caption Copyright Title Hawaiian green turtle severely afflicted with Fibropapillomatosis (FP) Caption Hawaiian green turtle (Chelonia mydas) severely afflicted with Fibropapillomatosis (FP) tumours. The mouth tumors, which are unique to Hawaiian greens, can occur inside the mouth and throat, impairing both breathing and feeding. Eye tumors impair vision and can blind the turtle. The large tumors around the flippers can impair swimming. Although FP tumors are benign, they can easily be a significant factor in a turtle's demise and result in death. Copyright ©Peter Bennett & Ursula Keuper-Bennett-1992 - CC BY 3.0 Hawaiian green turtle severely afflicted with Fibropapillomatosis (FP) Hawaiian green turtle (Chelonia mydas) severely afflicted with Fibropapillomatosis (FP) tumours. The mouth tumors, which are unique to Hawaiian greens, can occur inside the mouth and throat, impairing both breathing and feeding. Eye tumors impair vision and can blind the turtle. The large tumors around the flippers can impair swimming. Although FP tumors are benign, they can easily be a significant factor in a turtle's demise and result in death. ©Peter Bennett & Ursula Keuper-Bennett-1992 - CC BY 3.0 Title Green sea turtle with significant Fibropapilloma (FP) tumors Caption Green sea turtle (Chelonia mydas) with significant Fibropapilloma (FP) tumors. Basking on a beach, north of Hale'iwa, Hawaii, USA. November, 2011. Copyright ©Andrew Danielson-2011 - CC BY-SA 3.0 Green sea turtle with significant Fibropapilloma (FP) tumors Green sea turtle (Chelonia mydas) with significant Fibropapilloma (FP) tumors. Basking on a beach, north of Hale'iwa, Hawaii, USA. November, 2011. ©Andrew Danielson-2011 - CC BY-SA 3.0

Identity Top of page Preferred Scientific Name fibropapillomatosis of sea turtles International Common Names English: FP; green turtle fibropapillomatosis; marine turtle fibropapillomatosis; sea turtle virus

Overview Top of page Fibropapillomatosis (FP) is a disease of sea turtles that results in the production of tumours, both external and internal (i.e., visceral), that are considered benign, but may obstruct crucial functions, such as swimming, feeding, sight, and buoyancy, and can lead to death. It is presumed to be caused by Chelonid herpesvirus 5, although Koch’s postulates for proving the causal relationship have not yet been fulfilled due to the inability of the virus to grow in cell culture and the difficulties of experimentally infecting protected endangered species. It occurs most commonly in the green turtle (Chelonia mydas), which is currently listed as Endangered by the IUCN, but it has also been reported in the other six species of sea turtle, which (except for one for which there is insufficient data) are all classified as Vulnerable, Endangered or Critically Endangered. It was first reported in the 1930s in green turtles in Florida; it now has a worldwide, circumtropical distribution and is considered a pandemic, with infection rates above 70% in some regions.

Hosts/Species Affected Top of page Sea turtles, along with other turtles and tortoises, are part of the order Testudines. The seven living species include the green (Chelonia mydas), loggerhead (Caretta caretta), Kemp’s ridley (Lepidochelys kempii), hawksbill (Eretmochelys imbricata), flatback (Natator depressus), olive ridley (Lepidochelys olivacea), and the leatherback (Dermochelys coriacea). All species are in the family Cheloniidae, except the leatherback which belongs to the family Dermochelyidae. Fibropapillomatosis was first reported over 75 years ago in green turtles from Key West, Florida, USA (Smith and Coates, 1938). Initially, it was thought that it was confined to green turtles, but in recent years it has been found in all other species; however, prevalence is still greatest in C. mydas (Aguirre and Lutz, 2004; Foley et al., 2005).

Distribution Top of page Marine turtle fibropapillomatosis was first reported in the 1930s in green turtles (Chelonia mydas) in Key West, Florida, USA (Smith and Coates, 1938). C. mydas is globally distributed in tropical and subtropical oceans, normally between latitudes 40° N and 40° S (Hirth, 1997), nests in more than 80 countries and is believed to inhabit coastal waters of over 140 countries (Groombridge and Luxmoore, 1989). Fibropapillomatosis now has a worldwide, circumtropical distribution (Aguirre and Lutz, 2004) in C. mydas and other hosts, and has been reported from every major ocean basin in which green turtles are found, particularly in near-shore habitats.

Diagnosis Top of page Diagnosis of cutaneous fibropapillomatosis is made by gross pathological and histological examination of the tumours. Visceral fibropapillomas can be detected by radiography, MRI, and/or endoscopy. Several molecular polymerase chain reaction assays have been developed for the detection of Chelonid herpesvirus DNA from tumour tissues (Lu et al., 2000a; Lu et al., 2003; Quackenbush et al., 2001). Recently, a sensitive PCR assay was developed and validated for detecting the virus in clinically healthy turtles, presumably representing latent infection (Alfaro-Nunez and Gilbert, 2014). A serodiagnostic enzyme-linked immunosorbent assay to detect virus-specific antibodies has been developed; however, antibodies were detected only in samples collected after cutaneous fibropapillomas appeared (Herbst et al., 2008). Virus isolation is not currently possible as the virus has remained refractory to in vitro cultivation (Work et al., 2009).

Impact: Environmental Top of page Although fibropapillomatosis (FP) in sea turtles may have little environmental impact in and of itself, it is clear that there is a strong link between this disease and the environmental health of the coastal habitat (Santos et al., 2010, 2011). Sea turtles are often considered sentinels of ecosystem health (Aguirre and Lutz, 2004). In addition to infectious agents, they are particularly vulnerable to a variety of environmental insults such as high water temperature, pollutants, and marine biotoxins, all of which can impair their immune functions, making them more susceptible to a wide range of pathogens. In fact, it has been suggested that the epidemiology of FP could serve as an effective tool to monitor ecosystem health in near-shore marine habitats (Aguirre and Lutz, 2004). Unfortunately, all sea turtle species are in danger of becoming extinct in the near future. According to the IUCN Red List of Threatened Species, the hawksbill (Eretmochelys imbricata) and Kemp’s ridley (Lepidochelys kempii) turtles are listed as ‘critically endangered’; the loggerhead (Caretta caretta) and green (Chelonia mydas) turtles are listed as ‘endangered’; and the olive ridley (Lepidochelys olivacea) and leatherback (Dermochelys coriacea) turtles are listed as ‘vulnerable’ (IUCN, 2014). The flatback turtle (Natator depressus) is listed as ‘data deficient’, meaning that its conservation status is unclear due to lack of data; it was previously listed as ‘vulnerable’ (IUCN, 2014). There are many factors that contribute to the population decline of these animals. Some of these factors include harvesting for food, the illegal sea turtle shell trade, ingestion and entanglement of marine debris, artificial lighting, beach erosion, invasive species predation, marine pollution including oil spills, and warming of the oceans due to climate change (Sea Turtle Conservancy, 2015). FP and other diseases further add to the threats. Having said this, studies in Hawaii to date have failed to show a link between disease and effect on somatic growth rates (Chaloupka and Balazs, 2005), or adverse effects on population growth (Chaloupka et al., 2007).

Zoonoses and Food Safety Top of page Fibropapillomatosis is not zoonotic. However, the presence of the disease may suggest an ecological imbalance in the near-shore coastal environment that may directly or indirectly affect the human population.

Disease Treatment Top of page Surgical removal of the tumours is the most common treatment of affected turtles. Unfortunately, surgical excision is associated with a high rate of disease recurrence and secondary bacterial infections. Recently alternative therapies have been attempted. For example, Sellera et al. (2014) successfully used photodynamic therapy to remove lesions. For this procedure, the animal is given a systemic or local administration of a non-toxic photosensitizer - in this case, methylene blue. Then, the photosensitized target tissue is irradiated by visible or near-infrared low-intensity light at a specific wavelength and time to ‘activate’ the methylene blue molecules. In a trial of five affected green turtles (Chelonia mydas) that were treated twice at 15-day intervals, the treated lesions showed obvious tissue necrosis at 30 days post treatment, were totally or partially detached from the epidermis, and were easily removed using tweezers (Sellera et al., 2014). The potential for disease recurrence when this method is used is not known, however. Another promising treatment option for fibropapillomatosis is electrochemotherapy (Brunner et al., 2014). This technique uses a combination of chemotherapy, usually with bleomycin or cisplatin, and electroporation. It consists of a series of short, high-voltage electric pulses that lead to increased membrane permeability and more efficient transport of antineoplastic drugs through the cellular membrane. In a small study two green turtle fibropapillomas were treated in two sessions with a 33-day interval between sessions. In both animals, complete regression of the lesions occurred without side effects or complications (Brunner et al., 2014). Importantly, there was no sign of local recurrence, even one year after the end of treatment.

Prevention and Control Top of page Currently no prevention or control measures for wild populations of turtles are available, although the disease has been on a secular decline in Hawaii (Chaloupka et al., 2009), where turtles that strand with tumours are removed from the population (which is not the case in places where the disease persists). Given the association with environmentally polluted, near-shore coastal regions, it would make sense to attempt to clean up these areas as much as practical (which would benefit coastal marine ecosystems as a whole). In captivity, strict hygiene and quarantine procedures should be followed, including the use of separate water sources. Newly acquired animals should be kept isolated for a minimum of 3 months and should undergo thorough physical examinations both before and after quarantine. Preventive measures to reduce stress experienced by the animals in captivity may also help reduce mortality. Reduction in the number of animals per tank, high water quality, and optimal water temperature will help to reduce the number of animals affected in captivity.

Organizations Top of page USA: Sea Turtle Conservancy (STC), 4424 NW 13th St, Suite B-11, Gainesville, FL 32609, http://www.seaturtle.org/

Contributors Top of page 27/02/2015 Original text by: Chris A. Whitehouse, U.S. Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, Maryland 21702, USA

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