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

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.

Koch's postulates: Confirming Nannizziopsis guarroi as the cause of yellow fungal disease in Pogona vitticeps.

Nannizziopsis guarroi is an ascomycete fungus associated with a necrotizing dermatitis in captive green iguanas (Iguana iguana) and bearded dragons (Pogona vitticeps) across both Europe and North America. Clinical signs of the disease include swelling and lesion formation. Lesions develop from white raised bumps on the skin and progress into crusty, yellow, discolored scales, eventually becoming necrotic. The clinical signs are the basis of a colloquial name yellow fungal disease (YFD). However, until now, N. guarroi has not been confirmed as the primary agent of the disease in bearded dragons. In this experiment, we fulfill Koch's postulates criteria of disease, demonstrating N. guarroi as the primary agent of YFD in bearded dragons.

A precise relationship among Buller's drop, ballistospore, and gill morphologies enables maximum packing of spores within gilled mushrooms.

Basidiomycete fungi eject basidiospores using a surface tension catapult. A fluid drop forms at the base of each spore and, after reaching a critical size, coalesces with the spore and launches it from the gill surface. It has long been hypothesized that basidiomycete fungi pack the maximum number of spores into a minimal investment of biomass. Building on a nascent understanding of the physics underpinning the surface tension catapult, we modeled a spore's trajectory away from a basidium and demonstrated that to achieve maximum packing the size of the fluid drop, the size of the spore, and the distance between gills must be finely coordinated. To compare the model with data, we measured spore and gill morphologies from wild mushrooms and compared measurements with the model. The empirical data suggest that in order to pack the maximum number of spores into the least amount of biomass, the size of Buller's drop should be smaller but comparable to the spore size. Previously published data of Buller's drop and spore sizes support our hypothesis and also suggest a linear scaling between spore radius and Buller's drop radius. Morphological features of the surface tension catapult appear tightly regulated to enable maximum packing of spores. If mushrooms are maximally packed and Buller's drop radii scale linearly with spore radii, we predict that intergill distance should be proportional to spore radius to the power 3/2.