Development of Snake Fungal Disease after Experimental Challenge with Ophidiomyces ophiodiicola in Cottonmouths (Agkistrodon piscivorous)

Abstract

Snake fungal disease (SFD) is a clinical syndrome associated with dermatitis, myositis, osteomyelitis, and pneumonia in several species of free-ranging snakes in the US. The causative agent has been suggested as Ophidiomyces ophiodiicola, but other agents may contribute to the syndrome and the pathogenesis is not understood. To understand the role of O. ophiodiicola in SFD, a cottonmouth snake model of SFD was designed. Five cottonmouths (Agkistrodon piscivorous) were experimentally challenged by nasolabial pit inoculation with a pure culture of O. ophiodiicola. Development of skin lesions or facial swelling at the site of inoculation was observed in all snakes. Twice weekly swabs of the inoculation site revealed variable presence of O. ophiodiicola DNA by qPCR in all five inoculated snakes for 3 to 58 days post-inoculation; nasolabial flushes were not a useful sampling method for detection. Inoculated snakes had a 40% mortality rate. All inoculated snakes had microscopic lesions unilaterally on the side of the swabbed nasolabial pit, including erosions to ulcerations and heterophilic dermatitis. All signs were consistent with SFD; however, the severity of lesions varied in individual snakes, and fungal hyphae were only observed in 3 of 5 inoculated snakes. These three snakes correlated with post-mortem tissue qPCR evidence of O. ophiodiicola. The findings of this study conclude that O. ophiodiicola inoculation in a cottonmouth snake model leads to disease similar to SFD, although lesion severity and the fungal load are quite variable within the model. Future studies may utilize this model to further understand the pathogenesis of this disease and develop management strategies that mitigate disease effects, but investigation of other models with less variability may be warranted.

Fig 1. Sample collection for Snake Fungal Disease.

Collection of nasolabial swab (A) and flush (B) samples from cottonmouth (Agkistrodon piscivorous) experimentally challenged with Ophidiomyces ophiodiicola.

Fig 2. Facial swelling in Cottonmouths with Snake Fungal Disease.

Facial swelling observed in cottonmouths (Agkistrodon piscivorous) experimentally challenged with Ophidiomyces ophiodiicola. Severity ranged from severe (A, B), moderate (C), and mild (D).

Fig 3. Clinical signs of Snake Fungal Disease.

Graphs demonstrating the probability of facial swelling (A), skin lesions (B), and lethargy (C) in cottonmouths (Agkistrodon piscivorous) after experimental inoculation of the nasolabial pit with Ophidiomyces ophiodiicola. Solid line indicates the estimate, dashed lines indicate the 95% confidence interval, and open circles represent the presence or absence of the clinical sign.

Fig 4. Skin lesions in cottonmouths with Snake Fungal Disease.

Non-facial skin lesions observed in a cottonmouth (Agkistrodon piscivorous) experimentally challenged with Ophidiomyces ophiodiicola.

Fig 5. Snake Fungal Disease Histopathology.

Microscopic lesions in cottonmouth snakes inoculated with Ophidiomyces ophiodiicola. A. Normal nasolabial pit. HE stain. B. Nasolabial pit with epithelial thickening and crusts (arrowheads), erosion, ulceration, and dermatitis. Deeper in the head, there is osteomyelitis (asterisk). HE stain. C. Nasolabial pit with crusts and heterophilic dermatitis (arrowheads). HE stain. D. Granuloma deep to the nasolabial pit that contains intralesional fungal hyphae (black linear branching). GMS stain.