Fibropapillomatosis (FP) is a disease specific to sea turtles. The condition is characterized by benign but ultimately debilitating epithelial tumours on the surface of biological tissues. A herpesvirus is believed to be the causative agent of the disease, while turtle leeches are suspected mechanical vectors, transmitting the disease to other individuals. The disease is thought to have a multifactorial cause, including a tumour-promoting phase that is possibly caused by biotoxins or contaminants. FP exists all over the world, but it is most prominent in warmer climates, affecting up to 50%-70% of some populations.
Fibropapillomatosis is a benign tumor disease of marine turtles, predominantly in the green sea turtle, Chelonia mydas, but it has also been reported in the
Loggerhead Caretta Caretta,
Olive Ridley Lepidochelys Olivacea,
Kemp’s Ridley Lepidochelys Kempii, and
Leatherbacks Dermochelys coriacea.
This neoplastic disease causes proliferation of papillary cells (hyperplasia) and gives rise to excess fibrous connective tissue in both epidermal and dermal skin layers – or more specifically, proliferation of dermal fibroblasts and epidermal keratinocytes. This causes tumorigenesis in sizes less than 1 cm up to more than 30 cm in diameter. FP is most often found externally around the armpits, genitals, neck, eyes, and tails of turtles, but also occur in and around the mouth, and rarely in internal organs or on the carapace. This, in turn, impedes vision, feeding, and movement. Around 25-30% of turtles with external tumours also have internal tumours, primarily in heart, lungs and kidneys.
FP incidence is highest among immature and juvenile green turtles, while it is rare in adults. The suggestions for this pattern include the tumours can regress and be cured, which has been documented in some individuals, even when tumours were severe. However, the responses that cause these tumor regressions are unknown. Secondly, the juvenile individuals with FP might die before reaching adulthood.
The first documented case of the disease was in 1938 in Key West, Florida. Recent research has found that FP is caused by stress and tumours have been observed in turtles that are part of turtle tourism tours. It is thought that the presence of tourists causes the turtles stress The FP is an infectious disease with horizontal transmission. An alphaherpesvirus called fibropapilloma-associated turtle herpesvirus (FPTHV) is believed to be the causative agent of the disease, though no real proof of its causality exists. The reason for this belief is that nearly all tissue samples tested from turtles with lesions carry genetic material of this herpesvirus, varying between 95 and 100% depending on different studies and locations.
The leech genus Ozobranchus is thought to be the mechanical vector of the herpesvirus, transmitting the virus from one turtle to another. These leeches are common turtle ectoparasites that exclusively feed on turtle blood, and some leeches have been found carrying more than 10 million copies of the herpesvirus DNA. The green sea turtle is an herbivore and feeds primarily on seagrass and macroalgae. Two toxins which are suspected to be associated with FP are found epiphytically on these plants. First, the toxic compound lyngbyatoxin from the cyanobacterium Lyngbya majuscule, and second the toxin okadaic acid – a documented tumour-promoting toxin - from the dinoflagellate Prorocentrum. Again, causality has not been concluded, but an association seems to exist between the distribution of especially the dinoflagellates and the occurrence of FP, and as they are found on weeds, they can be ingested by foraging green sea turtles. Turtles with FP are found to have a compromised immune system.
Surgical removal of tumors caused by FP is the most common treatment method. Photodynamic therapy and electrochemotherapy are also used, as is CO2 laser surgery.Very expensive procedures. FP affects green sea turtle populations all over the world, making it a panzootic. It is especially found in warmer climates, such as the Caribbean, Hawaii, Japan, and Australia, where up to 70% of individuals in a population have FP.