Abstract
Fibropapillomatosis (FP) is a tumorigenic panzootic disease of sea turtles, most common in green turtles (Chelonia mydas). FP is linked to the chelonid alphaherpesvirus 5 (ChAHV5) and to degraded habitats and, though benign, large tumours can hinder vital functions, causing death. We analyse 108 green turtles, captured in 2018 and 2019, at key foraging grounds in Guinea-Bissau and Mauritania, West Africa, for the presence of FP, and use real-time PCR to detect ChAHV5 DNA, in 76 individuals. The prevalence of FP was moderate; 33% in Guinea-Bissau (n = 36) and 28% in Mauritania (n = 72), and most turtles were mildly affected, possibly due to low human impact at study locations. Juveniles had higher FP prevalence (35%, n = 82) compared to subadults (5%, n = 21), probably because individuals acquire resistance over time. ChAHV5 DNA was detected in 83% (n = 24) of the tumour biopsies, consistent with its role as aetiological agent of FP and in 26% (n = 27) of the ‘normal’ skin (not showing lesions) from FP turtles. Notably, 45% of the asymptomatic turtles were positive for ChAHV5, supporting multifactorial disease expression. We report the first baselines of FP and ChAHV5 prevalence for West Africa green turtles, essential to assess evolution of disease and future impacts of anthropogenic activities.
Highlights
In the past two decades, the human population has grown exponentially surpassing seven billion individuals in the year 2019 (United Nations 2019), leading to increased interactions between humans and wildlife, and to higher anthropogenic pressure on natural ecosystems, threatening the long-term survival of several species (Deem 2015)
Fibropapillomatosis (FP) is a tumorigenic disease that has been reported in all seven species of sea turtles; it is more frequent among green turtles (Chelonia mydas)
The minimal adequate generalized additive modelling (GAM) showed that the carapace length (CCL) was significantly correlated with FP risk at both sites (U&U: p = 0.023, Parc National du Banc d’Arguin (PNBA): GAM, p = 0.0003), at U& U the probability of developing FP was lower for smaller individuals increasing and peaking for turtles with CCL between 50–55 cm, decreasing thereafter ( Fig. 3a)
Summary
In the past two decades, the human population has grown exponentially surpassing seven billion individuals in the year 2019 (United Nations 2019), leading to increased interactions between humans and wildlife, and to higher anthropogenic pressure on natural ecosystems, threatening the long-term survival of several species (Deem 2015). Some infectious diseases with known major impacts on wildlife populations are chytridiomycosis in amphibians (Scheele et al 2017), canine distemper in carnivores (Kennedy et al 2000) and fibropapillomatosis in sea turtles (Work et al 2004). Fibropapillomatosis (FP) is a tumorigenic disease that has been reported in all seven species of sea turtles; it is more frequent among green turtles (Chelonia mydas). It was first reported in 1938 in a captive green turtle (Smith and Coates 1938), and ever since, it has been documented in sea turtle aggregations worldwide (Jones et al 2016)
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