A Cross-Inoculation Experiment Reveals that Ophidiomyces ophiodiicola and Nannizziopsis guarroi Can Each Infect Both Snakes and Lizards

Abstract

Host range and specificity are key concepts in the study of infectious diseases. However, both concepts remain largely undefined for many influential pathogens, including many fungi within the Onygenales order. This order encompasses reptile-infecting genera (Nannizziopsis, Ophidiomyces, and Paranannizziopsis) formerly classified as the Chrysosporium anamorph of Nannizziopsis vriesii (CANV). The reported hosts of many of these fungi represent a narrow range of phylogenetically related animals, suggesting that many of these disease-causing fungi are host specific, but the true number of species affected by these pathogens is unknown. For example, to date, Nannizziopsis guarroi (the causative agent of yellow fungus disease) and Ophidiomyces ophiodiicola (the causative agent of snake fungal disease) have been documented only in lizards and snakes, respectively. In a 52-day reciprocal-infection experiment, we tested the ability of these two pathogens to infect currently unreported hosts, inoculating central bearded dragons (Pogona vitticeps) with O. ophiodiicola and corn snakes (Pantherophis guttatus) with N. guarroi. We confirmed infection by documenting both clinical signs and histopathological evidence of fungal infection. Our reciprocity experiment resulted in 100% of corn snakes and 60% of bearded dragons developing infections with N. guarroi and O. ophiodiicola, respectively, demonstrating that these fungal pathogens have a broader host range than previously thought and that hosts with cryptic infections may play a role in pathogen translocation and transmission. IMPORTANCE Our experiment using Ophidiomyces ophiodiicola and Nannizziopsis guarroi is the first to look more critically at these pathogens' host range. We are the first to identify that both fungal pathogens can infect both corn snakes and bearded dragons. Our findings illustrate that both fungal pathogens have a more general host range than previously known. Additionally, there are significant implications concerning the spread of snake fungal disease and yellow fungus disease in popular companion animals and the increased chance of disease spillover into other wild and naive populations.

Keywords: CANV; Chrysosporium anamorph of Nannizziopsis vriesii; clinical experiment; emerging infectious disease; histopathology; host specificity; mycology; mycoses; snake fungal disease; spillover; yellow fungus disease.

FIG 1

Comparison of clinical signs of Ophidiomyces ophiodiicola and Nannizziopsis guarroi infections in corn snakes. (A) Corn snake infected with O. ophiodiicola. Note the severe swelling and thickening of the skin on the snout (white arrows indicate the extent of the swelling). (B) Corn snake infected with N. guarroi. Note the mild swelling and the lack of apparent scale thickening (white star). (C) Negative-control corn snake with no swelling, thickening, or lesions.

FIG 2

Clinical signs of disease on bearded dragons infected with N. guarroi and O. ophiodiicola. (A and B) One bearded dragon inoculated with N. guarroi with clinical signs 20 days (A) and 35 days (B) after inoculation. (C and D) One bearded dragon inoculated with O. ophiodiicola with clinical signs 20 days (C) and 41 days (D) after inoculation. Black solid arrows indicate areas of infection at abraded inoculated sites, black dashed arrows indicate areas of infection at nonabraded sites, and white stars indicate areas of swelling.

FIG 3

Photomicrographs of corn snakes (Pantherophis guttatus) and central bearded dragons (Pogona vitticeps) infected with Ophidiomyces ophiodiicola or Nannizziopsis guarroi. (A) Skin from the neck of a negative-control corn snake. A thin epidermis (arrow) overlies a sparsely cellular dermis (asterisk) and a deep muscular layer (diamond) (hematoxylin and eosin stain). (B) Skin from the neck of a negative-control bearded dragon. There is a thick stratum corneum (arrow), a thin epidermis, a sparsely cellular dermis (asterisk), and a deep muscular layer (diamond) (hematoxylin and eosin stain). (C) Skin from the head of a corn snake infected with O. ophiodiicola. The superficial epidermis is expanded by necrotic material (arrow), and the epidermis and dermis contain many granulocytic inflammatory cells (arrowheads) (periodic acid-Schiff stain). (D) Emphasized details of panel C at 20 μm of skin from the head of a corn snake infected with O. ophiodiicola. Many periodic acid-Schiff-positive fungal hyphae (arrows) and superficial conidia (arrowhead) are within the area of epidermal necrosis. (E) Skin from the neck of a bearded dragon infected with O. ophiodiicola. There is a large area of epidermal necrosis (asterisk). The dermis is expanded by abundant lymphoplasmacytic to histiocytic inflammatory cells (arrows) and contains a few fungal hyphae (arrowhead) (periodic acid-Schiff stain). (F) Details of the image in panel E of skin from the neck of a bearded dragon infected with O. ophiodiicola. The epidermis contains many fungal hyphae. There is a large cluster of conidia in the superficial epidermis (arrowhead), which underlies an area of discontinuity in the stratum corneum (arrow) (periodic acid-Schiff stain). (G) Skin from the head of a corn snake infected with N. guarroi. There is necrosis of the superficial epidermis (arrows). (Inset) Details of panel G. An area of epidermal necrosis underlies an area of discontinuity in the stratum corneum and contains low numbers of fungal hyphae (arrowhead) (periodic acid-Schiff stain). (H) Skin from the midbody of a bearded dragon infected with N. guarroi. The dermis is expanded by clear space (edema) and contains many fungal hyphae (arrows). There are conidia in the superficial epidermis within the crypt of a scale (arrowhead).