Jessica A. Farrell

The spreading global sea turtle fibropapillomatosis (FP) epizootic is threatening some of
Earth’s ancient reptiles, adding to the plethora of threats faced by these keystone species. Understanding
this neoplastic disease and its likely aetiological pathogen, chelonid alphaherpesvirus 5
(ChHV5), is crucial to understand how the disease impacts sea turtle populations and species and
the future trajectory of disease incidence. We generated 20 ChHV5 genomes, from three sea turtle
species, to better understand the viral variant diversity and gene evolution of this oncogenic virus.
We revealed previously underappreciated genetic diversity within this virus (with an average of
2035 single nucleotide polymorphisms (SNPs), 1.54% of the ChHV5 genome) and identified genes
under the strongest evolutionary pressure. Furthermore, we investigated the phylogeny of ChHV5 at
both genome and gene level, confirming the propensity of the virus to be interspecific, with related
variants able to infect multiple sea turtle species. Finally, we revealed unexpected intra-host diversity, with up to 0.15% of the viral genome varying between ChHV5 genomes isolated from different
tumours concurrently arising within the same individual. These findings offer important insights
into ChHV5 biology and provide genomic resources for this oncogenic virus.

Fibropapillomatosis (FP), a debilitating, infectious neoplastic disease, is rarely reported
in endangered Kemp’s ridley sea turtles (Lepidochelys kempii). With this study, we describe FP and
the associated chelonid alphaherpesvirus 5 (ChHV5) in Kemp’s ridley turtles encountered in the
United States during 2006–2020. Analysis of 22 case reports of Kemp’s ridley turtles with FP revealed
that while the disease was mild in most cases, 54.5% were adult turtles, a reproductively valuable
age class whose survival is a priority for population recovery. Of 51 blood samples from tumor-free
turtles and 12 tumor samples from turtles with FP, 7.8% and 91.7%, respectively, tested positive for
ChHV5 DNA via quantitative polymerase chain reaction (qPCR). Viral genome shotgun sequencing
and phylogenetic analysis of six tumor samples show that ChHV5 sequences in Kemp’s ridley
turtles encountered in the Gulf of Mexico and northwestern Atlantic cluster with ChHV5 sequences
identified in green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtles from Hawaii, the southwestern Atlantic Ocean, and the Caribbean. Results suggest an interspecific, spatiotemporal
spread of FP among Kemp’s ridley turtles in regions where the disease is enzootic. Although FP is
currently uncommon in this species, it remains a health concern due to its uncertain pathogenesis
and potential relationship with habitat degradation.

Fibropapillomatosis (FP) is a neoplastic disease most often found in green turtles (Chelonia
mydas). Afflicted turtles are burdened with potentially debilitating tumors concentrated externally on
the soft tissues, plastron, and eyes and internally on the lungs, kidneys, and the heart. Clinical signs
occur at various levels, ranging from mild disease to severe debilitation. Tumors can both progress
and regress in affected turtles, with outcomes ranging from death due to the disease to complete
regression. Since its official description in the scientific literature in 1938, tumor growth rates have
been rarely documented. In addition, FP tumors come in two very different morphologies; yet, to
our knowledge, there have been no quantified differences in growth rates between tumor types.
FP tumors are often rugose in texture, with a polypoid to papillomatous morphology, and may or
may not be pedunculated. In other cases, tumors are smooth, with a skin-like surface texture and
little to no papillose structures. In our study, we assessed growth-rate differences between rugose
and smooth tumor morphologies in a rehabilitation setting. We measured average biweekly tumor
growth over time in green turtles undergoing rehabilitation at the University of Florida Whitney
Laboratory Sea Turtle Hospital in St. Augustine, Florida, and compared growth between rugose and smooth tumors. Our results demonstrate that both rugose and smooth tumors follow a similar
active growth progression pattern, but rugose tumors grew at significantly faster rates (p = 0.013)
than smooth ones. We also documented regression across several examined tumors, ranging from
􀀀0.19% up to 􀀀10.8% average biweekly negative growth. Our study offers a first-ever assessment of
differential growth between tumor morphologies and an additional diagnostic feature that may lead
to a more comprehensive understanding and treatment of the disease. We support the importance of
tumor morphological categorization (rugose versus smooth) being documented in future FP hospital and
field-based health assessments.