Snake fungal disease: an emerging threat to wild snakes

Abstract

Since 2006, there has been a marked increase in the number of reports of severe and often fatal fungal skin infections in wild snakes in the eastern USA. The emerging condition, referred to as snake fungal disease (SFD), was initially documented in rattlesnakes, where the infections were believed to pose a risk to the viability of affected populations. The disease is caused by Ophidiomyces ophiodiicola, a fungus recently split from a complex of fungi long referred to as the Chrysosporium anamorph of Nannizziopsis vriesii (CANV). Here we review the current state of knowledge about O. ophiodiicola and SFD. In addition, we provide original findings which demonstrate that O. ophiodiicola is widely distributed in eastern North America, has a broad host range, is the predominant cause of fungal skin infections in wild snakes and often causes mild infections in snakes emerging from hibernation. This new information, together with what is already available in the scientific literature, advances our knowledge of the cause, pathogenesis and ecology of SFD. However, additional research is necessary to elucidate the factors driving the emergence of this disease and develop strategies to mitigate its impacts.This article is part of the themed issue 'Tackling emerging fungal threats to animal health, food security and ecosystem resilience'.

Keywords: North America; Ophidiomyces ophiodiicola; dermatitis; emerging disease; fungal infection; snake.

Figure 1.

Known distribution (as of April 2016) of Ophidiomyces ophiodiicola based on recovery of fungal isolates. Yellow dots depict records from captive snakes; red dots represent isolates from wild snakes. Note that some locations in close proximity may be represented by a single dot.

Figure 2.

Snakes with Ophidiomyces ophiodiicola infections of varying severity. Severe infections include (a) eastern foxsnake (Pantherophis vulpinus) with disfigured head, (b) eastern ratsnake (P. alleghaniensis) with lesions on the eye, snout and lower jaw, (c) timber rattlesnake (Crotalus horridus) with skin ulceration and (d) Lake Erie watersnake (Nerodia sipedon insularis) with areas of thickened, necrotic skin on ventral surface. Mild infections include bullsnakes (Pituophis catenifer sayi) with small lesions on (e) the lower jaw and (f) ventral scale (arrows).

Figure 3.

Moulting appears to be an important host response to infection by Ophidiomyces ophiodiicola. Most of the infected epidermis (seen here as thickened areas of yellow-brown skin) is cast off with the old skin (top). Post-moult, the skin at the site of a previous lesion is often grossly normal with the exception of some misshapen scales (arrow; bottom).