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Note. From Martínez-Ríos et al. (2025), Trachemys scripta eggs as part of a potential in vivo model for studying sea turtle egg fusariosis, licensed under CC BY 4.0. https://creativecommons.org/licenses/by/4.0/
Dermochelys coriacea
Caretta caretta
Chelonia mydas
Eretmochelys imbricata
Lepidochelys kempii
Lepidochelys olivacea
Natator depressus
Trachemys scripta
(Gleason et al., 2020:
Sea turtle egg fusariosis (STEF) is an emerging fungal disease that infects sea turtle eggs worldwide and is strongly associated with increased embryo mortality and reduced hatching success. The disease is caused by fungi belonging to the Fusarium solani species complex (FSSC), particularly Fusarium keratoplasticum (Fk) and Fusarium falciforme (Ff). These have been identified as the primary pathogens of STEF [11,5]. Certain Fusarium species, including Fk and Ff, can infect not only eggs but also multiple life stages of sea turtles [10]. Additionally, Fk and Ff can infect plants, marine animals, and humans [10,11,19]. These fungi have been detected in hospital environments and are known to cause infections such as keratitis, onychomycosis, and, in severe cases, widespread systemic infections [4,16].
The FSSC is a diverse fungal lineage that contains well over 60 species. These fungi are described as environmental saprophytes commonly found in soil, freshwater habitats, and plant debris. They obtain nutrients by decomposing organic matter [5,19]. Some species within this complex can act as pathogens by degrading eggshells and killing developing embryos. These fungi infect sea turtle eggs by forming a mycelial network (i.e., a web-like structure created by interconnecting hyphae) over the eggshell surface. These can degrade organic substrates and calcium carbonate, which weaken the eggshell and enable fungal hyphae to penetrate the egg and reach internal tissues. This is how necrotic lesions may develop, and certain species may produce mycotoxins that can diffuse into egg tissues, contributing to embryo mortality [9].
History
Initial reports of pathogenic Fusarium species in the United States were mainly linked with plant diseases. The earliest occurrence was reported in 1953, when Fusarium root rot was affecting soybeans in Iowa [1]. Research later revealed that certain Fusarium species could also infect humans and animals. For example, Fk was among the species responsible for an outbreak of contact lens-associated fungal keratitis affecting users in Southeast Asia and North America from 2005 to 2006 [21].
Solomon and Baird (1980), later cited in subsequent studies, provided one of the first reported correlations between fungal colonization of sea turtle eggs and developmental abnormalities [18]. Shortly after, a study looking into the causes of hatching failure within artificial and natural nests of sea turtle eggs, indicated the involvement of bacterial and fungal pathogens [22]. This led to the identification of Fusarium solani and others in the FSSC primary fungal pathogen [6,22]. Additionally, samples collected on Jekyll Island, Georgia between 2010 and 2012 detected FSSC species, predominantly Fk and Ff, in loggerhead sea turtle eggs. This represented the first detection in North America, providing further evidence for the global distribution of these fungal pathogens [2].
Clinical Signs and Progression
Note. From Carranco et al. (2022), Transcending sea turtles: First report of hatching failure in eggs of an Amazonian freshwater turtle with symptoms of the fungal emerging disease fusariosis, licensed under CC BY-NC 4.0. https://creativecommons.org/licenses/by-nc-nd/4.0/
STEF initial signs of infection include discoloration on the surface of eggshells (e.g., red, blue, grey, and yellow areas). Progression of infection may be indicated by the presence of hyphal mats on the outer shell and eventual penetration into internal tissue and embryos [14,16,21]. The spread into internal tissues and embryos is strongly influenced by necrotic lesions. As the embryo becomes increasingly compromised, hatching success declines significantly and often fails (Figure 1) [9]. Although signs of infection can sometimes be visible, some eggs may show no clear signs, meaning they are asymptomatic (Figure 1) [16,21]. As certain Fusarium species can also infect hatchlings, juveniles, and adults, clinical signs have also been observed in these life stages. These clinical signs include discoloration, loss, and lesions of the shell and skin [10].
Transmission and Epidemiology
Note. From Martinez-Rios et al. (2025), Trachemys scripta eggs as part of a potential in vivo model for studying sea turtle egg fusariosis, licensed under CC BY 4.0. https://creativecommons.org/licenses/by/4.0/
Certain environmental factors have been linked to increased Fusarium species infection in nests, such as areas with regular tidal flooding and higher slit and clay content [18]. Additional factors that can contribute to infection include temperature, moisture, and pH. For example, like other microorganisms, higher nest temperatures can not only promote microbial growth and infection but also increase the vulnerability of affected species [11]. Fusarium sp. infection in sea turtles is found globally across Asia, Africa, Australia, North and South America, and Europe [9]. The highest incidence of STEF has been reported in coastal regions bordering the Indian, Pacific, and Atlantic Oceans. Additionally, the disease has also been observed in both the Caribbean and Mediterranean Sea [10]. In the United States, Florida and Georgia have been reported to have STEF infections [2,11]. Locations where these pathogens can be found include plant tissues, human tissues, plastics, contact lenses, sink drains, and plumbing systems [9,11]. Because their environmental presence is widespread, FSSC can also be difficult to identify and prevent their emergence.
Diagnosis
The initial diagnosis of STEF is made through a physical examination, especially by looking for discoloration and hyphal mats within the outer shell. A microscopic examination is then performed on samples collected from the eggshell, shell fragments, or embryonic fluid of the affected individual. Structures such as hyphae and conidia are highly associated with fungal infection. A histological examination involves staining of affected tissue to observe extensive fungal growth [4,20]. Fungal isolation and deoxyribonucleic acid (DNA) extraction are performed before polymerase chain reaction (PCR) testing. PCR testing is used to identify specific pathogens [8].
Treatment and Prevention
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Although treatment options are limited prevention methods could offer better management of this disease. In captive settings, basic hygiene should be enforced, such as frequent disinfection, handwashing, and the use of masks and gloves [8]. However, studies have noted that washing eggs is not enough to fully prevent infection. Environmental reservoirs, such as soil or sand, play a significant role in transmission [7,14]. Therefore, in captive settings, regularly replacing these substrates can help reduce exposure. Additionally, humidity and temperature should be maintained within optimal ranges to prevent stress in embryos [7]. Other preventive measures can be implemented to reduce the disposal of trash near nesting habitats, particularly given the risk that plastic harbors fungal pathogens (Figure 3) [9,11].
Further Research
Research is needed on the following topics: treatment and prevention strategies; the effects of Fusarium keratoplasticum (Fk) and Fusarium falciforme (Ff) infections on hatching success; and how environmental factors influence infection [21]. Since the pathogens responsible for STEF can affect a wide range of hosts, from humans to plants, many areas require further research. Additionally, while research has largely focused on STEF, bacterial communities in sea turtle eggs should be further studied and differentiated to determine their impact on hatching success [15]. Continuous surveillance of STEF is also essential for managing and controlling the spread of this emerging disease, as it can significantly improve hatching success and reduce egg mortality.
Readings
1. Arias, M. M. D., Munkvold, G. P., Ellis, M. L., & Leandro, L. F. S. (2013). Distribution and frequency of Fusarium species associated with soybean roots in Iowa. Plant Disease, 97(12), 1557-1562. https://doi.org/10.1094/PDIS-11-12-1059-RE
2. Bailey, J. B., Lamb, M., Walker, M., Weed, C., & Craven, K. S. (2018). Detection of potential fungal pathogens Fusarium falciforme and F. keratoplasticum in unhatched loggerhead turtle eggs using a molecular approach. Endangered Species Research, 36, 111-119. https://doi.org/10.3354/esr00895
3. Cabanes, F. J., Alonso, J. M., Castella, G., Alegre, F., Domingo, M., & Pont, S. (1997). Cutaneous hyalohyphomycosis caused by Fusarium solani in a loggerhead sea turtle (Caretta caretta L.). Journal of Clinical Microbiology, 35(12), 3343-3345. https://doi.org/10.1128/jcm.35.12.3343-3345.1997
4. Cafarchia, C., Paradies, R., Figueredo, L. A., Iatta, R., Desantis, S., Di Bello, A.V. F., Zizzo, N., & van Diepeningen, A. D. (2020). Fusarium spp. in loggerhead sea turtles (Caretta caretta): From colonization to infection. Veterinary Pathology, 57(1), 139-146. https://doi.org/10.1177/030098581988
5. Carranco, A. S., Gillingham, M. A. F., Wilhelm, K., Torres, M. de L. T., Sommer, S., & Romo, D. (2022). Transcending sea turtles: First report of hatching failure in eggs of an Amazonian freshwater turtle with symptoms of the fungal emerging disease fusariosis. Transboundary and Emerging Diseases, 69(5), e3282-88. https://doi.org/10.1111/tbed.14596
6. Fisher, M. C., Henk, D. A., Briggs, C. J., Brownstein, J. S., Madoff, L. C., McCraw, S. L., & Gurr, S. J. (2012). Emerging fungal threats to animal, plant, and ecosystem health. Nature, 484(7393), 186-194. https://doi.org/10.1038/nature10947
7. Garcia-Hartmann, M., Hennequin, C., Catteau, S., Beatini, C., & Blanc, V. (2017). Clusters of Fusarium solani infection in juvenile captive – born Caretta caretta sea turtles. Journal Of Medical Mycology, 27(1), 113-118. https://doi.org/10.1016/j.mycmed.2016.12.001
8. García-Martín, J. M., Sarmiento-Ramírez, J. M., & Diéguez-Uribeondo, J. (2021). Beyond sea turtles: Fusarium keratoplasticum in eggshells of Podocnemis unifilis, a threatened Amazonian freshwater turtle. Journal of Fungi, 7(9), 742. https://doi.org/10.3390/jof7090742
9. Gleason, F. H., Allerstorfer, M., & Lilje, O. (2020). Newly emerging diseases of marine turtles, especially sea turtle egg fusariosis (SEFT), caused by species in the Fusarium solani complex (FSSC). Mycology, 11(3), 184-194. https://doi.org/10.1080/21501203.2019.1710303
10. Greeff-Laubscher, M. R., & Jacobs, K. (2022). Fusarium species isolated from post-hatchling loggerhead sea turtles (Caretta caretta) in South Africa. Scientific Reports, 12, 5874. https://doi.org/10.1038/s41598-022-06840-1
11. Kuschke, S. G., Wyneken, J., Cray, C., Turla, E., Kinsella, M., & Miller, D.L. (2023). Fusarium spp. an emerging fungal threat to leatherback (Dermochelys coriacea) eggs and neonates. Frontiers in Marine Science, 10, id.1170376. https://doi.org/10.3389/fmars.2023.1170376
12. Lo, P.-H., Huang, J.-H., Chang, C.-C., Namisy, A., Chen, C.-Y., & Chung, W.-H. (2025). Diversity and characteristics of Fusarium solani species complex (FSSC) isolates causing collar rot and fruit rot of passion fruit in Taiwan. Plant Disease, 109(1), 170-182. https://doi.org/10.1094/PDIS-06-24-1161-RE
13. Martínez-Rois, M., Martín-Torrijos, L., & Dieguez-Uribeondo, J. (2022). The invasive alien red-eared slider turtle, Trachemys scripta, as a carrier of STEF-disease pathogens. Fungal Biology, 126(2), 113-121. https://doi.org/10.1016/j.funbio.2021.11.003
14. Martínez-Ríos, M., Martín-Torrijos, L., & Diéguez-Uribeondo, J. (2025). Trachemys scripta eggs as part of a potential in vivo model for studying sea turtle egg fusariosis. Journal of Fungi, 11(1), 23-34. https://doi.org/10.3390/jof11010023
15. McMaken, C. M., Burkholder, D. A., Milligan, R. J., & Lopez, J. V. (2023). Potential impacts of environmental bacteria on the microbiota of loggerhead (Caretta caretta) and green (Chelonia mydas) sea turtle eggs and their hatching success. Microbiology Open, 12(3), e1363. https://doi.org/10.1002/mbo3.1363
16. Nardoni, S., & Mancianti, F. (2023). Mycotic diseases in chelonians. Journal of Fungi, 9(5), 518. https://doi.org/10.3390/jof9050518
17. Nucci, M., & Anaissie, E. (2007). Fusarium infections in immunocompromised patients. Clinical Microbiology Reviews, 20(4), 695-704. https://doi.org/10.1128/CMR.00014-07
18. Phillott, A. D., Parmenter, C J., & McKillup, S. C. (2006). Calcium depletion of eggshell after fungal invasion of sea turtle eggs. Chelonian Conservation and Biology, 5(1), 146-149. https://scispace.com/pdf/calcium-depletion-of-eggshell-after-fungal-invasion-of-sea-34ox7sqaiq.pdf
19. Sarmiento-Ramírez, J. M., Abella-Pérez, E., Phillott, A. D., Sim, J., van West, P., Martín, M. P., Marco, A., & Dieguez-Uribeondo, J. (2014). Global distribution of two fungal pathogens threatening endangered sea turtles. PLoS ONE, 9(1), e85853. https://doi.org/10.1371/journal.pone.0085853
20. Saenz, V., Lizcano-Salas, A. F., Pabon, K., Jauregui, A., Caballero, S. & Ramirez, A. M. C. (2025). Sea turtle egg fusariosis (STEF): A possible threat to species of sea turtle in Colombia. One Health Mycology, 1(2), 79-90. https://doi/10.63049/OHM.24.12.3
21. Smyth, C. W., Sarmiento-Ramírez, J. M., Short, D. P. G., Diéguez-Uribeondo, J., O'Donnell, K., Geiser, D. M. (2019). Unraveling the ecology and epidemiology of an emerging fungal disease, sea turtle egg fusariosis (STEF). PLoS Pathogens, 15(5), e1007682. https://doi.org/10.1371/journal.ppat.1007682
22. Wyneken, J., Burke, T. J., Salmon, M., & Pedersen, D. K. (1988). Egg failure in natural and relocated sea turtle nests. Journal of Herpetology, 22(1), 88-96. https://www.jstor.org/stable/1564360