A basic understanding of the ecology and physiology of fungal pathogens causing emerging infectious diseases in wildlife is lacking. Experiments delineating the host range of pathogens are rare, resulting in inaccurate inferences of a disease’s impact on different species in any given ecosystem. Diseases including snake fungal disease (SFD), caused by Ophidiomyces ophiodiicola, and yellow fungus disease (YFD), caused by Nannizziopsis guarroi, afflict reptile species and, until now, were thought to only infect snakes and lizards, respectively. SFD is currently spreading in North America and causing devastating population declines in wild rattlesnake species. We sought to test if O. ophiodiicola is capable of infecting other animals, potentially causing disease in naïve wild populations and exacerbating spillover effects into domestic populations of reptiles. We ran a cross-inoculation experiment using the two fungal pathogens, and two animal hosts, corn snakes (Pantherophis guttatus) and bearded dragons (Pogona vitticeps).
Results/Conclusions
Ophidiomyces ophiodiicola and N. guarroi were each capable of infecting both corn snakes and bearded dragons, expanding the known host range of both pathogens. Bearded dragons inoculated with O. ophiodiicola exhibited a range of clinical signs in response to infection. Animals ranged from asymptomatic to developing gross lesions. Although the body condition of the bearded dragons did not decline, histological analyses revealed evidence of epidermal invasion by fungal elements (hyphae or conidia), confirming O. ophiodiicola can infect animals other than snakes. Corn snakes inoculated with N. guarroi never developed thickened scales or gross lesions, clinical signs often associated with dermatophytic fungal infections. However, as with bearded dragons, despite appearing asymptomatic, histological analyses revealed epidermal invasion of fungal elements, confirming N. guarroi can infect animals other than lizards. Our experiment is the first to reveal O. ophiodiicola is capable of infecting hosts other than snake species, suggesting a much larger host range exists than previously thought, which validate concerns of spillover effects into domestic reptile populations. Furthermore, our experiment is the first to confirm N. guarroi as the causative agent of YFD in bearded dragons by simultaneously fulfilling Koch’s postulates and revealing YFD is capable of infecting hosts other than lizards.