Mycotic Diseases of Reptiles

Excessively high humidity, low environmental temperature, concurrent disease, malnutrition, inappropriate antimicrobial therapy, and other stressors may predispose reptiles to development of various mycoses. Little is known about the pathogenesis of systemic mycoses, which can develop over a long period; however, maintaining proper management and nutrition decreases the frequency of infection.

Members of the phyla Microsporidia, Zoopagomycota, Mucoromycota, Basidiomycota, and Ascomycota (including Ophidiomyces and Nannizziopsis) have been associated with disease in reptiles. Diagnosis requires histological demonstration of a host pathological response and identification of the mycotic agent.

Reports of successful treatment of systemic mycoses in reptiles are few. Suggested treatments for deep fungal respiratory infections include amphotericin B, itraconazole, fluconazole, and voriconazole (see image of tortoise being treated with amphotericin B). For superficial or localized mycotic infections, surgical removal of the granuloma with local wound treatment is advised. Basidiobolus spp, which are pathogenic for mammals, are found in feces of healthy reptiles.

Pulmonary candidiasis, tortoise

Image

Courtesy of Dr. Stephen Divers.

Nannizziopsis spp, in the order Onygenales, family Nannizziopsiaceae, have been recognized as a major concern in squamates. They are commonly known by reptile hobbyists as the causative organisms of “yellow fungus disease,” although nannizziomycosis may be a better term. Patients initially develop crusting dermatitis; however, invasion of deeper tissues is common, and fatality rates are high. In much of the literature, unfortunately, the fungal species involved were initially misidentified as “Chrysosporium anamorph of Nannizziopsis vriesii (CANV),” resulting in confusion. The term CANV should not be used.

Ophidiomyces ophiodiicola has been recognized as a major concern in North American snakes. The clinical presentation of the organism is commonly called “snake fungal disease,” although ophidiomycosis is a better term. Also initially misidentified in reports as Chrysosporium anamorph of Nannizziopsis vriesii, O ophiodiicola was first characterized in 2009, with snakes developing crusting dermatitis, often distributed around the head. Invasion of deeper tissues is possible. The disease is capable of causing population-level impacts on some free-ranging populations. Normal cutaneous flora inhibit the growth of O ophiodiicola, so antimicrobial use may predispose animals to developing ophidiomycosis.

Dermatophytosis has been described in all orders of reptiles. Geotrichum, Fusarium, and Trichosporon are the genera most frequently isolated. In most cases, cutaneous injury precedes a secondary fungal infection. Chelonians with fungal infections of the shell can be treated by local debridement and topical application of Lugol solution or povidone-iodine. Exposure to UV light also may be beneficial.

Ulceration of GI tissues has been associated with infections by Mucor and Fusarium spp. Chronic visceral granulomatous disease of liver, kidneys, and spleen has been caused by Metarhizium and Paecilomyces spp. Few clinical signs other than weight loss are observed before death. Animals may continue to feed until a few days before death.

The most frequent sites of mycotic infection are the skin and respiratory tract. Metarhizium, Mucor, and Paecilomyces spp are frequent isolates. Aspergillus and Candida spp have been isolated from pulmonary lesions of lizards and chelonians. Most infections involve granuloma or plaque formation with resultant clinical signs of respiratory distress before death. Candidiasis in large snakes has been treated with nystatin (100,000 U, PO, for 10 days).