Equine Pulmonary Cryptococcosis: A Comparative Literature Review and Evaluation of Fluconazole Monotherapy

Abstract

Cryptococcus is the most common fungal respiratory pathogen in Australian horses, manifesting primarily as pulmonary granulomas. Disease severity at presentation is dependent on the athletic use of the horse. The diagnosis and estimation of disease severity are centred around clinical findings, cytological evaluation of respiratory tract secretions, diagnostic imaging, and antigen titre testing. Both the lateral flow assay and the latex cryptococcal antigen titre are used, and important similarities and differences between species are discussed. Cryptococcus gattii occurs with greater frequency than Cryptococcus neoformans in equine pulmonic cryptococcosis and can be successfully treated with enteral fluconazole monotherapy, with disease severity determining treatment length.

Antifungal non‐invasive soak under general anaesthetic to treat fungal rhinitis in an Australian Quarter Horse gelding at pasture

“…The pathophysiology of fungal rhinitis is unknown, but in most cases it is associated with predisposing factors such as immunosuppression or disruption of the respiratory defence mechanisms permitting penetration of the mucosa by opportunistic fungal organisms . The underlying predisposition in the present case is unknown and clinically there were no signs of immunosuppression.…”

“…In addition, the release of a generic fluconazole now means that it is both readily available and affordable in comparison to alternative antifungal agents such as itraconazole and voriconazole, which can be cost‐prohibitive when considering the large volumes required for systemic administration or topical flushing and bathing . Hepatotoxicity linked with fluconazole therapy has been described in human literature, but has not been seen in horses . Amphotericin B is an effective antifungal agent, but we did not choose it, because of its potential nephrotoxic effects and associated high costs .…”

“…Hepatotoxicity linked with fluconazole therapy has been described in human literature, but has not been seen in horses . Amphotericin B is an effective antifungal agent, but we did not choose it, because of its potential nephrotoxic effects and associated high costs . Nystatin, natamycin and miconazole were also disregarded, because of their reportedly low efficacy in horses .…”

Severe cryptococcal granulomas of the nasopharynx in a horse treated with standing endoscopic laser surgery and oral fluconazole

“…; Secombe et al . ). The pathogen is considered an opportunistic, saprophytic, basidiomycetous yeast.…”

“…Although definitive predisposing causes of upper respiratory tract fungal infections are not routinely established, infection occurs when one or more criteria are met; there is sufficient infectious dose; exposure to a virulent strain or susceptible host immune status (Secombe et al . ). It is ubiquitous worldwide as is the distribution of clinical cases and although most have been reported from Western Australia (Riley et al .…”