Virus detected even in tumor-free turtles — Genomic signals from 8 individuals in Singapore

Sea turtle virus in Singapore The study revealed something unprecedented. Upon re-examining genomic data from eight green and hawksbill sea turtles—including individuals showing no visible tumors—DNA signals of a virus linked to neoplastic disease were identified in all of them.

However, interpreting these results to mean that “the presence of the virus inevitably leads to tumors” would be completely incorrect. This is because no significant difference in the number of viral sequences was found between individuals with tumors and those without. The core message of the paper is less about the presence of the infection itself, but rather under what conditions the infection manifests as disease.(continued from above)

30-Second Summary

• Whole-genome sequencing data from four green sea turtles and four hawksbill sea turtles obtained in Singapore between 2020 and 2022 were analyzed.
• Both methods—reference genome alignment and metagenomic analysis— Scutavirus chelonidalpha5 detected the relevant sequences in all eight individuals.
• While visible tumors were observed in only two green sea turtles, viral signals were detected even in asymptomatic individuals.
• The difference in the number of viral sequences based on the presence or absence of tumors was not statistically significant (p=0.1905).
• Due to the small sample size (eight individuals) and the lack of histological confirmation of the lesions, it is impossible to draw definitive conclusions regarding the overall regional infection rate or causal relationships.

What happened?

On August 18, 2026, researchers at Nanyang Technological University Frontiers in Amphibian and Reptile Science reported the first molecular detection of the virus in wild sea turtles in Singapore. Scutavirus chelonidalpha5 This virus was formerly known as chelonid alphaherpesvirus 5 (ChHV5) and is associated with fibropapillomatosis (FP), a condition that causes tumors in sea turtles.

Target Species Information

“Research method: Searching for viral traces in the host genome

Samples were obtained from individuals that had stranded or come ashore to nest between 2020 and 2022. Among the four green sea turtles, two exhibited visible external tumors on their necks and flippers, as well as internal lung tumors. No visible tumors were found on the four hawksbill sea turtles. The research team utilized whole-genome data from six blood samples and one sample each of liver and muscle tissue.

The first analysis employed the BWA-MEM method to align DNA fragments against a viral reference genome. The second was a Kraken2 metagenomic analysis, which classified sequences against a viral database after removing host sequences. A key strength of this study is the comparison of whether these two distinct approaches detected the same signals.

Key Results and Figures

Reference alignment detected virus-related sequences in all eight individuals; normalized values ​​(adjusted for total read count) ranged from 30,869 to 98,326. Normalized values ​​from the metagenomic analysis ranged from 178 to 488. The results from both methods showed a positive correlation (Spearman ρ=0.79, p=0.048).

However, differences between green sea turtles and hawksbill sea turtles (p=0.057) and between individuals with and without tumors (p=0.1905) did not reach statistical significance. Notably, one muscle sample was excluded from statistical analysis due to an excessive number of unclassified sequences.

Why is this important?

Surveys based solely on visual inspection may overlook asymptomatic infections. This is because the virus can remain latent, and detection levels vary depending on the tissue type or stage of infection. Repurposing whole-genome data demonstrates the potential to extract pathogen surveillance information from existing genomic datasets.

NOAA explains that fibropapillomatosis causes tumors not only on the skin but also on internal organs; in severe cases, this can interfere with vision, feeding, and swimming. This implies that in urbanized coastal areas like Singapore, factors such as pollution, nutrient levels, water temperature, immune status, and microbial communities must be monitored alongside the presence of the virus.

Points to avoid overinterpreting

This study is neither a prevalence survey claiming that “most sea turtles in Singapore are infected” nor a causal experiment proving the virus directly caused the tumors. The sample consisted of eight individuals—including stranded ones—selected for convenience, so it is not representative of the entire population. Tumors were classified only by visual appearance; without access to histopathological records, they could not be definitively diagnosed as FP. It is also unknown whether individuals without tumors developed the disease later.

4 Key Takeaways

• Viral DNA was detected in all eight individuals.
• Individuals without tumors also tested positive, making it difficult to determine infection status based on visual observation alone.
• The mere presence of the virus The onset of the tumor cannot be explained.
• Larger organ samples, histological diagnoses, and data on water quality, immunity, and microbiota are required.

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• Study of 48 relocated sea turtle nests
• Temperature-dependent sex determination in turtles and primary cilia
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Original source, DOI, and references

• Tanabe et al. (2026), Frontiers in Amphibian and Reptile Science — DOI 10.3389/famrs.2026.1814588
• IUCN 2025 Red List update: Global assessment of green sea turtles (LC) “— Populations in certain regions have separate threat classifications
• NOAA Fisheries: Fibropapillomatosis FAQ
• Singapore NParks: Hawksbill Turtles