Filamentous fungi in cold-blooded animals
Most of us are used to deal with fungal diseases on humans and other mammals. The spectrum of etiologic agents between hosts is mostly relatively comparable; Candida, Aspergillus and dermatophytes are prevalent on humans as well as on dogs (Guillot et al. 2023), cats (Danesi et al. 2022) and ruminants (Jensen & Becker 2022). However, when we go lower down into the vertebrate phylogenetic tree, entirely different fungi are encountered, most of which are as yet still poorly investigated. Well-known examples are the reptile diseases by members of Nannizziopsis (Bertelsen et al. 2005; McEntire et al. 2021) and Paranannizziopsis (Sigler et al. 2013), or the Platypus having the single species Mucor amphibiorum as a prevalent pathogen (Connolly 2022).
Two groups of human opportunists behave entirely different on non-human animals. Fusarium and black yeast-like infections, known as hyalo- and phaeohyphomycoses, respectively, are important human disease entities. A wide range of Fusarium species is involved in human onychomycoses (Yang et al. 2011) and keratitis (Tupaki-Sreepurna et al. 2017), and fungemia are noted in severely immunocompromised patients (Yun et al. 2007). For black fungi. The numerous disseminated cases in patients with CARD9-related immunodeficiency are remarkable (Wang et al. 2019), in addition to brain infections (Garg et al. 2007) and mutilating chromoblastomycosis (Queiroz-Telles et al. 2017), but on other mammals these fungi are quite exceptional. This kind of infections is practically unknown in other warm-blooded animals.
Janse et al. (2024) recently provided an overview of fungal diseases in fish. Only a limited number of species is concerned. Remarkably, a significant difference was noted in host choice of hyaline versus melanized fungi. Fusarium and some other hyaline fungi were nearly exclusively found in cartilaginous fish (sharks and allies), while black yeast-like fungi (Exophiala and allies) and Scolecobasidium species almost only infected bony fish. The selective preference is even more pronounced if other cold-blooded animals are compared. Fusarium, and another hyaline fungus, Purpureocillium lilacinum are often found infecting turtles; even a specific, named disease on turtle eggs (STEF: sea turtle egg fusariosis) has been described (Martínez-Ríos et al. 2022). In contrast, black yeast-like fungi are known to infect and kill toads and frogs (Stupar et al. 2017). The reason for this bipartition in cold-blooded host choice is unknown.
All above fungal genera, with numerous representing species with further reading can be found in the Atlas of Clinical Fungi. The general search function provides a wealth of information. For example, the keyword ‘keratitis’ delivered 171 species, and ‘CARD9’ 25 species. Subscribers also have access to some chapters of the future Atlas of Veterinary Fungi.
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