Abstract

Since the 1980's, sea turtle fibropapillomas have emerged as a significant cause of morbidity and mortality of sea turtles worldwide. Fibropapillomatosis is considered a visible marker of sea turtle health and is associated with damaged marine ecosystems. While late stage disease is well described, there is controversy in the literature regarding causative agents and early skin changes are poorly understood. The objective of this study was to histologically examine grossly normal skin biopsies of loggerhead sea turtles off Bahia Magdalena, Baja California Sur, Mexico for changes suggestive of early cutaneous lesions. Biopsies were collected from 58 live caught loggerhead turtles (Caretta caretta).

Histologic changes were restricted to the epidermis. Mild histologic changes were observed in 38 (62%) of the biopsies. The most common observation was a variable amount of cytoplasmic vacuolation that was most prominent in areas of acanthosis or papillary projections. Epidermal thickness was variable both within and between samples. Acanthosis, up to 20 cell layers thick, was observed in 29 biopsies. Animals with cytoplasmic vacuolation were nine times more likely to also have areas of hyperplasia than those without. Of these sections in which epidermal hyperplasia were present, the number of papillary projections was increased in 11 animals; however, this was not statistically associated with cytoplasmic vacuolation. Keratin was mildly thickened in 29 animals. Hyperkeratosis was 15 times more likely to be present in animals with cytoplasmic vacuolation than animals without. Other histologic changes identified included aggregates of superficial bacteria and fungi devoid of associated inflammatory response and one animal with superficial, heterophilic pustules. Rare apoptotic keratinocytes were occasionally observed. Papillomavirus was detected in 2 of the skin biopsy samples by polymerase chain reaction (PCR).

In many species, preneoplastic epidermal changes including hyperplasia and dysplasia are well understood. Similar changes are also well described in other species with papillomavirus infection. Histologic changes identified in the present study were subtle and the significance of these changes is difficult to interpret. Given the ecological significance of sea turtle fibropapillomatosis, further investigation of the early dermal changes may elucidate important information regarding the pathogenesis of the disease.