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Note. From Schilliger et al., (2023), Major emerging fungal diseases of reptiles and amphibians, licensed under CC BY 4.0. https://creativecommons.org/licenses/by/4.0/
Pogona vitticeps
Pogona barbata
Iguana iguana
Eumeces inexpectatus
Agama agama
Intellagama lesuerurii
Phelsuma sp.
Calumna parsonii
Furcifer lateralis
Trioceros jacksonii
Eublepharis macularius
Tiliqua multifasciata
(Cabanes et al., 2014; Keller et al., 2023; Sigler et al., 2013)
Nannizziomycosis, formerly known as yellow fungus disease, is caused by various Nannizziopsis species, including N. draconii, N. guarroi, N. barbatae, N. chlamydospore, and N.dermatidis. Although this shows a wide range of causative agents, N. guarroi has primarily been reported in lizards. Nannizziomycosis affects multiple lizard species but is most common in bearded dragons (Pogona vitticeps) [8]. Nannizziopsis spp. has been formerly grouped under the fungal complex, Chrysosporium anamorph of Nannizziopsis vriesii (CANV), which also contained Paranannizziopsis spp. and Ophidiomyces spp. These species contain well-known fungal pathogens that cause disease in reptiles, especially infectious dermatomycosis [2,9]. The CANV complex has primarily been observed to have keratinolytic activity, enabling the fungus to colonize and degrade keratinous substrates, including reptilian skin. Additionally, these species are generally considered primary pathogens that cause disease in healthy individuals but have also been observed to act as opportunistic fungi, causing disease in injured or stressed individuals [5].
Fungal infection from nanizziomycosis begins with hyphae proliferation in the superficial layer of the skin (stratum corneum), followed by progressive invasion into the deeper epidermal layers and dermis [8]. Nannizziopsis species can grow across a range of temperatures. N. guarroi exhibits growth in temperatures between 20 and 35 degrees Celsius, but they often grow faster at 35 degrees Celsius. However, N. chlamydospore growth is inhibited at 35 degrees Celsius, and N. barbatae does not exhibit growth at any temperature above this [3,8].
History
In 1991, species within the CANV complex were first described to cause disease in day geckos (Phelsuma sp.) imported from Madagascar to Germany. Following this, reports of disease in Canada in 1997 affected various chameleon species, including Chamaeleo lateralis, Chamaeleo jacksoni, and Calumma parsonii [6,9]. In the 2000s, the term "yellow fungus disease" was established to refer to the disease caused by CANV, which led to yellow discoloration of the outermost layer of the skin in captive bearded dragons [1,12]. Years later, N. guarroi was first recognized in green iguanas in Spain, which were thought to have acquired the pathogen through the European pet trade. Additionally, examinations of previous fungal infections in bearded dragons found N. guarroi in the United States as early as 1992 in Wisconsin [9]. In 2013, Nannizziopsis species were originally described as infecting free-ranging lizards in Australia; however, by 2020, deadly cases of nannizziomycosis affecting wild lizards were found in Australia. The causative agent of these infections was N. barbatae. These cases represented the first documented infection in a wild population [7].
Clinical Signs and Progression
Note. From Peterson et al., (2020), Cross-continental emergence of Nannizziopsis barbatae disease may threaten wild Australian lizards, licensed under CC BY 4.0. https://creativecommons.org/licenses/by/4.0/
Skin lesions, often distributed throughout the body, limbs, face, and even the tail, are an initial clinical sign of nannizziomycosis (Figure 1). The severity of these lesions often varies, with ulceration, necrotic changes, discoloration, swelling, crusting, and subcutaneous masses (Figure 2) [10]. Discoloration from this disease was often described as yellow to brown, hence the previous name, yellow fungus disease [4]. Further progression of the disease can lead to systemic lesions affecting bone and muscle [5,11]. In some cases, skin lesions are absent, but systemic infection is present [11]. Additional clinical signs associated with nannizziomycosis include anorexia, lethargy, and failure of normal skin shedding [8,12].
Transmission and Epidemiology
Nannizziomycosis is highly contagious among reptiles, as evidenced by its high environmental persistence [2,3,10]. For example, studies have reported that N. guarroi survives on surfaces (e.g., stainless steel, cotton, glass, and hard plastic) and in water-based environments for approximately 14 days [4]. Additionally, direct contact with infected individuals and skin shedding can make species vulnerable to infection. Fungal elements, such as hyphae and spores, of Nannizziopsis species can serve as an additional means of transferring infection. Dispersal methods for these elements include airborne transfer, which can result in direct contact with individuals or the environment [3].
Species belonging to the CANV complex have been recognized as infecting a wide variety of reptiles, including lizards, snakes, and crocodiles [9]. Nannizziomycosis has been identified in affected reptiles in North America, Europe, Africa, Asia, New Zealand, and Australia [8]. Lizard species are the primary hosts affected by Nannizziomycosis. The animal trade has played a significant role in exposing unaffected individuals to infection [9].
Diagnosis
Note. From Peterson et al., (2020), Cross-continental emergence of Nannizziopsis barbatae disease may threaten wild Australian lizards, licensed under CC BY 4.0. https://creativecommons.org/licenses/by/4.0/
The initial diagnosis of nannizziomycosis is based on the appearance of skin lesions and other previously described clinical presentations. Microscopic examination of these skin lesions is used to identify branching fungal hyphae and arthroconidia within the tissues (Figure 3). Additional findings include hyperkeratosis, necrosis, inflammatory cells, and hyperplasia [5,7]. Although fungal cultures do not provide species-level identification, they are used to confirm colony morphological similarities to other fungi (Figure 3) [4]. Radiographs (X-rays) and computed tomography (CT) can be used to examine the spread of infection to the bones [7]. Next-generation sequencing (NGS) is a diagnostic test commonly used in clinical settings and provides more comprehensive results. NGS has been able to detect nannizziomycosis even before lesion development [11,12].
Treatment and Prevention
Similar to other fungal diseases in reptiles, antifungal medications have been used to treat nannizziomycosis. This includes ketoconazole, itraconazole, and voriconazole [2,5]. However, these medications have not always resulted in complete elimination of the disease, as in some cases, skin lesions reappear. If an infected individual presents with subcutaneous masses, surgical removal of the tissue can be performed. Progression of disease, affecting quality of life, can also result in euthanization [10].
Enforced quarantine procedures for sick or infected individuals can help prevent the spread of disease. Additional caution should be practiced when acquiring new animals. Surfaces, equipment, and enclosures should be disinfected using 10% bleach. Disinfectant can also be used on gloves to prevent contamination when handling animals. Persistent monitoring should continue and be enhanced to control the spillover of disease into wild populations and different regions of the world [8].
Further Research
Nannizziomycosis has been around for a long time, but some areas require further research to develop strategies to control its spread. Researchers need to investigate the role of environmental drivers (i.e., persistence of fungus across various environmental parameters), treatment failure (i.e., antifungal medications and the regression of lesions/disease), and the host immune response [4]. Additionally, reptilian natural microbiota should be further explored to identify associations between the roles of different bacterial and fungal organisms in disease [12].
Readings
1. Bowman, M. R., Paré, J. A., Sigler, L., Naeser, J. P., Sladky, K. K., Hanley, C. S., Helmer, P., Phillips, L. A., Brower, A., & Porter, R. (2007). Deep fungal dermatitis in three inland bearded dragons (Pogona vitticeps) caused by the Chrysosporium anamorph of Nannizziopsis vriesii. Medical Mycology, 45(4), 371–376. https://doi.org/10.1080/13693780601188610
2. Cabanes, F. J., Sutton, D. A., & Guarro, J. (2014). Chrysosporium-related fungi and reptiles: A fatal attraction. PLoS pathogens, 10(10), e1004367. https://doi.org/10.1371/journal.ppat.1004367
3. Dalen, J. P., Wong, A. D., Adamovicz, L., Liszka, N. C., & Keller, K. A. (2026). Detection of viable Nannizziopsis guarroi in housing environments prior to dermatological lesion development in bearded dragons (Pogona vitticeps). Animals, 16(2), 275. https://doi.org/10.3390/ani16020275
4. Keller, K. A., Durante, K., Foltin, E., & Cerreta, A. J. (2023). Nannizziopsis guarroi has prolonged environmental persistence on clinically relevant substrates. Journal of the American Veterinary Medical Association, 261(S1), S109–S113. https://doi.org/10.2460/javma.22.12.0575
5. Mitchell, M. A., & Walden, M. R. (2013). Chrysosporium anamorph Nannizziopsis vriesii: An emerging fungal pathogen of captive and wild reptiles. The Veterinary Clinics of North America, 16(3), 659–668. https://doi.org/10.1016/j.cvex.2013.05.013
6. Paré, J. A., Sigler, L., Hunter, D. B., Summerbell, R. C., Smith, D. A., & Machin, K. L. (1997). Cutaneous mycoses in chameleons caused by the Chrysosporium anamorph of Nannizziopsis vriesii (Apinis) Currah. Journal of Zoo and Wildlife Medicine, 28(4), 443–453. http://www.jstor.org/stable/20095688
7. Peterson, N. R., Rose, K., Shaw, S., Hyndman, T. H., Sigler, L., Kurtböke, D. İ., Llinas, J., Littleford-Colquhoun, B. L., Cristescu, R., & Frère, C. (2020). Cross-continental emergence of Nannizziopsis barbatae disease may threaten wild Australian lizards. Scientific Reports, 10(1), 20976. https://doi.org/10.1038/s41598-020-77865-7
8. Schilliger, L., Paillusseau, C., François, C., & Bonwitt, J. (2023). Major emerging fungal diseases of reptiles and amphibians. Pathogens, 12(3), 429. https://doi.org/10.3390/pathogens12030429
9. Sigler, L., Hambleton, S., & Paré, J. A. (2013). Molecular characterization of reptile pathogens currently known as members of the Chrysosporium anamorph of Nannizziopsis vriesii complex and relationship with some human-associated isolates. Journal of Clinical Microbiology, 51(10), 3338–3357. https://doi.org/10.1128/JCM.01465-13
10. Schmidt-Ukaj, S., Loncaric, I., Spergser, J., Richter, B., & Hochleithner, M. (2016). Dermatomycosis in three central bearded dragons (Pogona vitticeps) associated with Nannizziopsis chlamydospora. Journal of Veterinary Diagnostic Investigation, 28(3), 319–322. https://doi.org/10.1177/1040638716636422
11. Wong, A. D., Adamovicz, L., Dalen, J. P., Bender, A. M., Rosser, M. F., Imai, D. M., Terio, K. A., Reinhart, J. M., Allender, M. C., & Keller, K. A. (2025). Multiple diagnostic modalities are appropriate for detecting Nannizziopsis guarroi in experimentally infected bearded dragons (Pogona vitticeps). Frontiers in Amphibian and Reptile Science, 3, 1607686. https://doi.org/10.3389/famrs.2025.1607686
12. Zapanta, K., Kavanagh, M., Keller, K., Nguyen, L., Rosenkrantz, W., & Krumbeck, J. A. (2025). The cutaneous microbiota and nannizziomycosis in bearded dragons (Pogona vitticeps): Associations between infectious Nannizziopsis species and common bacterial pathogens. Veterinary Dermatology, 36(4), 506–515. https://doi.org/10.1111/vde.13360