Avian Candidiasis: A Comprehensive Review of Pathogenesis, Diagnosis, and Control

This review is a comprehensive investigation of avian candidiasis, mainly caused by Candida albicans, although the prevalence of non-albicans Candida species has increased in domestic and wild birds. Avian candidiasis causes significant economic losses in poultry production through increased mortality, cost of treatments, and reduced growth rates, particularly in young birds and intensive farming operations. The pathogenesis section provides a description of the molecular virulence factors such as adhesin-mediated attachment (ALS, Agglutinin-Like Sequence family; HWP1, Hyphal Wall Protein 1), yeast-to-hypha morphogenesis, tissue damage by Candidalysin, biofilm formation on mucosal and abiotic surfaces, and secreted hydrolytic enzymes including secreted aspartyl proteinases (SAPs) and phospholipases. The identified predisposing factors include immunosuppression, malnutrition, abuse of antibiotics, bad husbandry, and crop stasis. The diagnostic methods discussed encompass cytological analysis and fungal culture on selective media to more sophisticated methods of molecular analysis (PCR, MALDI-TOF MS, and NGS). Antifungal susceptibility investigations indicate that nystatin and amphotericin B are still very effective against most avian isolates and that resistance to the azoles is on the rise, especially with respect to the non-albicans Candida species. Nystatin is still the first-line treatment of localized infections; azoles are still used for resistant or systemic infections despite their hepatotoxicity. Sanitation, proper nutrition, and proper use of antimicrobials are essential to prevent diseases. The knowledge gaps comprise the absence of avian-specific pharmacokinetic information, poor knowledge of species-species virulence phenotypes, and the lack of point-of-care diagnostics. The need to have integrated One Health surveillance systems is emphasized by the zoonotic potential of the avian Candida reservoirs.