Introduction
Most fungi that cause disease in humans can also cause invasive infections in different animal species and may be associated with significant morbidity and mortality (Fisher et al.
2012; Kohler et al. 2015). In addition, infections of the hair, skin, and nails, allergy, and mycotoxicoses may also occur in animals (Yanong 2003; Seyedmousavi et al. 2013a, 2015a), although often caused by related but nonidentical species.Antifungal therapy remains a central component of protecting human and animals against fungal infections (Rochette et al. 2003). An ideal antifungal agent is a drug that selectively destroys fungal pathogens with minimal side effects to the host (Seyedmousavi et al. 2017). Depending on the strategy chosen, topical and/or systemic antifungal drugs can be used based on the clinical picture and the species identification of the etiologic agent (Seyedmousavi et al. 2017).
Despite recent advances in antifungal pharmacology, therapeutic options against fungal infections in animals are limited, because (a) very few options are available in the existing chemical drug classes with antifungal activity (Kathiravan et al. 2012) and (b) only a few products are licensed for animals. However, off-label use of antifungals is quite common, and many of the antifungal agents that are used in humans are also used in animals (Foy and Trepanier 2010). These drugs include the polyenes (e.g., amphotericin B and nystatin), the azoles including both the imidazoles and triazoles, the allylamines (e.g., terbinafine), the echinocandins and the nucleoside analogs. Many of the limitations observed for these drugs in humans also occur in some animal species, including variable pharmacokinetics, adverse effects, and drug interactions (Lewis 2011). However, differences for these agents are also observed between humans and animals. Resistance to antifungals can also occur in different animal species that receive these drugs (Beernaert et al. 2009a; Wang et al. 2013; Singer et al. 2014; Ziolkowska et al. 2014; Cafarchia et al. 2015), although the true epidemiology of antifungal resistance in animals is unknown, and options to treat infections by resistant fungi are limited.
The present chapter discusses the currently available classes and representatives of systemic antifungal drugs used in both human and animals. The development and epidemiology of antifungal resistance in animals are also reviewed.
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