Novel disease state model finds most juvenile green turtles develop and recover from fibropapillomatosis

Abstract

Fibropapillomatosis (FP) is a sea turtle disease characterized by benign tumor development on the skin, eyes, and/or internal organs. It primarily affects juvenile green turtles (Chelonia mydas) in coastal foraging sites. The Indian River Lagoon (IRL), Florida, USA, is a coastal green turtle foraging site where the observed FP annual rate averaged 49% between 1983 and 2018. While FP is no longer considered a major cause of sea turtle mortality and most individuals fully recover, the overall dynamics of this disease are poorly understood because prior disease history is unknown for individuals without FP at capture time, and future disease outcome is unknown for individuals with FP at capture time. To better evaluate FP dynamics for green turtles in the IRL, we developed a hierarchical model for predicting disease state change. We used data from 4149 captures of 3700 individual green turtles captured in the IRL. The hierarchical disease state model contained two levels: Level 1 modeled whether an individual would develop FP, and Level 2 modeled disease state progression, including states for pre-FP affliction, active FP affliction, and full recovery from FP. From the hierarchical model, we estimated 99.8% (95% credibility intervals 99.1%-100%) of juvenile green turtles in the IRL developed FP, indicating that nearly every individual in the IRL is affected by this disease. The model also suggested that turtles quickly developed FP upon recruitment to the IRL and then recovered at different rates, with most completely recovering before emigrating from the IRL as they mature. This is the first analysis of long-term sea turtle data suggesting nearly every turtle in an aggregation both develops and recovers from FP.

Exploring the relationship between environmental drivers and the manifestation of fibropapillomatosis in green turtles (Chelonia mydas) in eastern Brazil

“…Assuming a similar growth rate in FP-affected and FP-free turtles, as documented in previous studies [ 67 ], this suggests that the FP-affected turtles were on average slightly older than FP-free turtles in this cohort, possibly reflecting the time lapse associated with the onset and growth of FP tumors upon arrival to the neritic habitat. On the other hand, FP occurrence gradually decreased in turtles with CCL greater than 70 cm, which is consistent with tumor remission (as suggested by disease state modelling studies [ 68 ]), development of disease resistance, or death/removal of affected individuals.…”

Spatial distribution of fibropapillomatosis in green turtles along the Queensland coast and an investigation into the influence of water quality on prevalence

“…Alternatively, upon recruitment to inshore areas from their pelagic existence, green turtles in Australia undergo an ontogenetic shift in diet (Arthur, Boyle, & Limpus, 2008). It may be possible that stress from the dietary shift from an omnivorous to herbivorous diet in new recruits is associated with the increase in susceptibility to FP (Bolten et al, 2003; Jones & Seminoff, 2013; Kelley et al, 2022). Moreover, as green turtles consume macroalgae, mangrove fruit, and seagrass (Arthur et al, 2009; Brand‐Gardner et al, 1999; Prior et al, 2015; Read & Limpus, 2002), either food source or the combination of both could be contributing to this susceptibility.…”

“…The tumors may limit or obstruct the vision, feeding, and locomotive ability of affected turtles (Jones et al, 2016) and as a result, these turtles may be at increased risk of predation, starvation, and boat‐strike. The consequences of tumors on infected individuals can vary, with both mortality (Chaloupka et al, 2008) and complete recovery reported (Limpus et al, 2016; Machado Guimarães et al, 2013) and modeled (Kelley et al, 2022). In depth understanding of the effects of this disease on marine turtle populations as a whole is still a missing piece in the evidence‐based management of this endangered species.…”

Green Turtle Fibropapillomatosis: Tumor Morphology and Growth Rate in a Rehabilitation Setting

“…Differences between progression and regression patterns were previously found among different age cohorts of green turtles in Hawaii, with adult nesters reporting a significantly higher rate of FP tumor regression compared to juveniles [ 10 ]. There are further reports of spontaneous tumor regression [ 11 ], and some modeling studies suggest that most affected individuals eventually recover from FP [ 12 ]. However, this recovery assessment was based on 72 animals captured with FP and subsequently re-captured without FP, and there was no firm input in the modelling of how many turtles with FP subsequently died and therefore were not recaptured, as this is an unknown variable in the dataset [ 12 ].…”

“…There are further reports of spontaneous tumor regression [ 11 ], and some modeling studies suggest that most affected individuals eventually recover from FP [ 12 ]. However, this recovery assessment was based on 72 animals captured with FP and subsequently re-captured without FP, and there was no firm input in the modelling of how many turtles with FP subsequently died and therefore were not recaptured, as this is an unknown variable in the dataset [ 12 ]. Therefore, there is generally a lack of published data on turtles that had FP but were not monitored or re-captured in the wild, potentially skewing any modelling or observation towards only those individuals that survived to be re-captured.…”