A 1 year old bearded dragon developed chronic crusty lesions over the body, face and tail. Skin biopsies were taken and submitted to VPG Histology for examination. This revealed epidermal hyperplasia and prominent hyperkeratosis, areas of superficial epidermal necrosis and a mild inflammatory infiltrate within the epidermis and dermis. Faint outlines of structures suspected to represent fungal hyphae and spores were observed in the keratin layer.

The skin biopsy showing hyperplasia of the epidermis (E) and a prominent keratin layer (K).

A PAS stain revealed numerous fungal hyphae (long arrows) and conidia (short arrows) in the keratin layer.

These findings indicate a fungal infection. The histological features of the fungal organisms, together with the clinical presentation support a diagnosis of “yellow fungus disease”.

‘Yellow fungus disease’ is a dermatomycosis of bearded dragons. The disease presents initially with crusty lesions of hyperkeratosis, progressing to yellow or brown discoloured areas and eventually cutaneous necrosis. Areas of necrosis may slough, resulting in ulcerated lesions. Progression to underlying tissues and systemic dissemination may occur (1).

A fungus previously termed ‘Chrysosporium anamorph of Nannizziopsis vriesii’ (CANV) has been isolated from such lesions (2) . Fungi with similar features have also been identified in other reptile species, including green iguanas, chameleons, snakes and crocodiles. Further analysis of these isolates has led to reclassification of the fungi, and the species most commonly associated with yellow fungus disease in bearded dragons is now considered to be Nannizziopsis guarroi (3,4). Other species previously classified as CANV include Nannizziopsis dermatitidis isolated from chameleons, N. crocodilii (saltwater crocodiles), Paranannizziopsis australasiensis (bearded dragons and snakes) and Ophidiomyces opiodiicola (snakes).

Unlike many other fungi, which act as opportunistic pathogens, fungi of the former CANV-complex are considered primary pathogens of reptiles and are contagious. Stress and overcrowding are predisposing factors.

A minimum of 2 minutes of exposure to a 10% dilution of commercial bleach has been recommended for disinfection of surfaces and instruments contaminated with N. guarroi (5)

Histopathological examination of skin biopsies identifies fungal hyphae and conidia. Further confirmation can be obtained by using fungal culture or PCR analysis.

The zoonotic risk is considered to be very low. Rare cases of infections with fungi, suspected to represent a CANV-like species have been reported in immunocompromised patients, but further analysis indicated that these may represent a distinct lineage, separate from the reptile species. Nevertheless, reptiles may be carriers of a range of pathogens, including Salmonella spp.,  and good hygiene is therefore essential in particular in households with immunocompromised individuals.

1. Pare J., Sigler L. Fungal Diseases in Mader’s Reptile and Amphibian Medicine and Surgery.Saunders Elsevier; St. Louis, Missouri, USA: 2006. pp. 217–226.
2. Bowman MR, Paré JA, Sigler L, Naeser JP, Sladky KK, Hanley CS, Helmer P, Phillips LA, Brower A, Porter R. (2007).Deep fungal dermatitis in three inland bearded dragons (Pogona vitticeps) caused by the Chrysosporium anamorph of Nannizziopsis vriesii. Med Mycol. Jun;45(4):371-6.
3. Schilliger L, Paillusseau C, François C, Bonwitt J. (2023) Major Emerging Fungal Diseases of Reptiles and Amphibians. Pathogens. Mar 8;12(3):429.
4. Sigler L, Hambleton S, Paré JA. (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. J Clin Microbiol. 51(10):3338-57.
5. Jourdan B., Hemby C., Allender M.C., Levy I., Foltin E., Keller K.A. (2023) Effectiveness of Common Disinfecting Agents Against Isolates of Nannizziopsis guarroi.  Herpetol. Med. Surg. 33(1), 40-44.