Signalment:  

2-year-old male inland bearded dragon, Pogona vitticeps.A 2-year-old male bearded dragon was living in a glass terrarium with sand substrate, UVB light, and a basking bulb as a classroom pet. The animal presented with a 3-week history of multifocal raised nodules on its dorsum, ventrum, and head; several of which were exfoliating upon manual examination revealing areas of ulceration. Impression smears obtained from ulcerations on the dorsum, ventrum, neck, and above the left eye were suggestive of fungal infection with evidence of granulomatous inflammation. The owner elected euthanasia due to poor prognosis of medical treatment efficacy.

Gross Description:  

Post mortem examination identified bilaterally symmetrical, circular, oval areas of yellow discoloration on the ventral abdomen that each measured 3.5x3 cm, extending onto the proximal limbs, ventral neck, and head. Multifocally, there were also raised, irregular, firm lesions with thickened epidermis in the left periorbital region (1.5x1.5 cm), on the left caudal mandible (3x2.5x1 cm), on the right dorsal neck (2,5x2 cm), and on the right body wall caudal to the thoracic limb (2x1.5 cm). On cut surface, these raised lesions consisted of poorly defined, firm, whitish nodules, surrounded by pale yellow, soft tissue of gelatinous consistency. The skin also had multiple annular areas of ulceration: above the left eye (2x2 cm), left dorsum (2x2 cm), and ventrally between the thoracic limbs (1.5x1 cm). No other abnormalities were noted at necropsy. 

Histopathologic Description:

Skin: Alterations in all sections of the examined raised skin lesions from different areas are similar and, thus, will be described collectively. There are extensive areas of ulceration flanked by epidermis with extensive chromatophore accumulation just beneath the epidermal basal lamina. The superficial epidermis has multifocal areas of degeneration, characterized by vacuoles filled with eosinophilic, proteinaceous cellular debris and overall loss of cellular stratification. At the interface of the ulcerated and intact epidermis, the stratum corneum is moderately thickened with no retention of nuclei (orthokeratotic hyperkeratosis). The dermis is moderately expanded by edema and inflammatory cell infiltrate, composed of heterophils and macrophages. Underlying the ulcerated regions, the dermis is markedly expanded by multifocal to coalescing granulomas within dense fibrous connective tissue. Granulomas are composed of necrotic centers, surrounded by concentrically arranged epithelioid macrophages interspersed with heterophils and multinucleated giant cells, and encapsulated by fibroblasts. The dense connective tissue surrounding and separating the granulomas is markedly infiltrated by heterophils, macrophages, lymphocytes, and plasma cells. Overlying the granulomas and replacing the epidermis is extensive necrotic cellular debris admixed with hemorrhage, aggregates of dark yellow-to-brown pigment, and dense tufts of arthroconidia and hyphae embedded within dense layers of keratin. Occasional fungal organisms, similar to those described previously, are also identified within the granulomas and loosely within the dermal connective tissue. The subcutis contains mild inflammatory cellular infiltrates, consisting of heterophils, lymphocytes, plasma cells, and mast cells, with random foci of necrosis.

In sections of the ventral abdomen, deep layers of the epidermis contain multifocal, round, expansile aggregates of myriad fungal spores and hyphae. Fungal aggregates are primarily encased in dense keratin, and other times they are found clustered within the superficial stratum corneum. Fungal organisms are similar to those described above in the raised skin lesions. Commonly, arthroconidia are identified among the hyphae as well as free within the nearby epidermis. Epidermal changes surrounding the fungal aggregates include moderate dilation of intercellular spaces (spongiosis), ballooning degeneration, and mild transmigration of heterophils. Segmentally, in close proximity to the fungal organisms, the stratum corneum displays moderate orthokeratotic hyperkeratosis. In the underlying dermis, there is moderate infiltrate composed mainly of heterophils, lymphocytes, plasma cells and macrophages. 

Morphologic Diagnosis:  

Skin: Proliferative and ulcerative dermatitis, granulomatous, multifocal, chronic, severe, with myriad intralesional segmented hyphae and arthroconidia.

Lab Results:  

Mycology culture: Chrysosporium sp. isolate.
PCR: Nannizziopsis guarroi based on DNA sequence analysis of the ITS and D1/D2 regions (performed at the University of Texas Health Sciences Center).

Condition:  

Nannizziopsis guarroi

Contributor Comment:  

While the majority of fungal organisms affecting reptiles are believed to be opportunistic, Nannizziopsis sp. have been suggested as obligate fungal pathogens of reptiles. An infectious model with veiled chameleons fulfilled Koch's postulate in transmitting what is now known to be Nannizziopsis dermatitidis via application of the fungus to intact and abraded skin, with subsequent development of the lesions observed naturally. N. dermatitidis. was also determined to be infectious via direct contact and/or through fomite transmission in the same study.(3)

The Nannizziopsis species seen most commonly in bearded dragons and green iguanas is N. guarroi.(1,2) The disease is often called Yellow Fungus Disease by hobbyists because the crusts found on bearded dragons tend to have yellow discoloration. Thus, crust formation, color change and necrosis are commonly seen in these cases. Lesions tend to be multifocal and may include the head, oral cavity, limbs, ventrum and dorsum. The infection is often aggressive, with extension into the subcutaneous tissues, muscles, and bones.(3) In some cases there is also systemic spread to the lungs and liver after local cutaneous invasion.(3)

This inland bearded dragon had multifocal raised nodules on the skin, with multiple areas of ulceration and an irregular oval area of yellow discoloration on the ventral head, neck and abdomen, with no evidence of extension into underlying muscle and/or bone. Microscopically the raised nodules consisted of granulomatous proliferative dermatitis. Additionally, there was superficial ulceration with myriad intralesional segmented hyphae and arthroconidia, which by mycological culture and PCR were identified as Nannizziopsis guarroi. 

Recently, morphologically similar isolates formerly referred to as members of the CANV complex, have been properly identified into three genera: Nannizziopsis, Paranannizziopsis, and Ophidiomyces, which are not particularly closely related within the Onygenales. The genus Nannizziopsis was split into 8 unique species: N. vriesii, N. dermatitidis, N. crocodili, N. barbata, N. guarroi, N. infrequens, N. hominis, and N. obscura. Benefits of this classification scheme include clarification of the range of susceptible hosts for each fungal species, monitoring trends of infection, determination of the prevalence of specific species in the environment, ability to evaluate species-specific antifungal efficacy, and development of specific strategies for disease prevention.(4)

N. guarroi is a keratinophilic ascomycetous fungus that has been associated with several cases of granulomatous dermatitis in toxicoferan squamates. Due to the inherent stress that may accompany classroom pets related to frequent handling and/or taunting, the role of stress cannot be ruled out in the susceptibility to the fungal infection in this case. N. guarroi do not grow at 40^°C and hospitalizing reptiles at increased temperatures during treatment may help the patient eliminate the fungus. Additionally, laboratories may be underreporting N. guarroi infections if culture protocols call for temperatures in excess of 37^°C (false negatives), stressing the importance of communication with laboratories in suspected N. guarroi cases.(2)

JPC Diagnosis:  

Skin: Ulcerative crusting dermatitis, with granulomatous inflammation and intralesional fungal elements, etiology consistent with Nannizziopsis guarroi.

Conference Comment:  

N. guarroi dermatomycosis is a contagious disease that can have severe consequences for reptile collections. Hyphal proliferation occurs initially within the superficial dead epidermal layers.(3) As with many skin diseases in reptiles, the scale fold becomes an excellent media for infection as keratin becomes impacted. From here, hyphae penetrate downward pushing through the basement membrane. The fungal invasion can continue beyond the dermis into the subjacent musculature.(3) Necrotizing cutaneous infections can progress to systemic disease and may become fatal.(2)

Fungi have used a nomenclature inconsistent with the rest of biology. There are separate genus and species names for asexual anamorph stages and sexual teleomorph stages of the same organism, resulting in multiple species names and paraphyletic taxa. In 2011, it was decided by the Nomenclature Section meeting of the International Botanical Congress that teleomorph names should be used (Hawksworth, 2011). This is problematic for medicine, as nearly all names of systemic fungi routinely used are anamorph names (e.g. Cryptococcus, Blastomyces, Histoplasma, Aspergillus, etc.). The anamorph genus Chrysosporium is widespread across the tree of the fungal order Onygenales, and contains organisms in more than 15 teleomorph genera, including Nannizziopsis. Many Chrysosporium sp. infecting reptiles have been morphologically misidentified as Chrysosporium anamorph of Nannizziopsis vriesii (CANV)

Recent publications have identified Nannizziopsis guarroi as the most common cause of yellow skin disease in bearded dragons.(1,5) This correlates with PCR findings in this case, and further illustrates the inaccuracy of the term CANV for this entity. 

*Special thanks to Dr. Jim Wellehan, Asst. Professor at the University of Florida College of Veterinary Medicine for his contributions to this case*

References:

1. Abarca ML, Castella G, Martorell J, Cabanes FJ. Chrysosporium guarroi sp. nov. a new emerging pathogen of pet green iguanas (Iguana iguana). Med Mycol. 2010;48:365-372.

2. Abarca ML, Martorell J, Castell+�-� G, Ramis A, Caba+�-�es FJ. Der- matomycosis in a pet inland bearded dragon (Pogona vitticeps) caused by a Chrysosporium species related to Nannizziopsis vriesii. Vet. Dermatol. 2009;20:295299.

3. Hawksworth DL. A new dawn for the naming of fungi: impacts of decisions made in Melbourne in July 2011 on the future publication and regulation of fungal names. MycoKeys. 2011;1: 720.

4. Par+�-� JA, et al. Pathogenicity of the Chrysosporium Anamorph of Nannizziopsis vriesii for veiled chameleons (Chamaeleo calyptratus). Medical Mycology. 2006;44:25-31. 

5. Sigler L, et al. Molecular characterization of reptile pathogens currently known as members of Chrysosporium anamorph of Nannizziopsis vriesii complex and relationship with some human-associated isolates. Journal of Clinical Microbiology. 2013;51:3338-3357.

6. Stchigel AM, Sutton DA, Cano-Lira JF, et al. Phylogeny of chrysosporia infecting reptiles: proposal of new family Nannizziopsiaceae and five new species. Persoonia. 2013;31:86-100.