Saccharomycotina yeasts in humans, animals and the environment: A call for integrated one health action

Subphylum Saccharomycotina includes yeasts with broad ecological, manufacturing, medical and veterinary clinical significance and encompasses Candida spp. and related genera. While some, like Candida albicans, are frequently encountered as opportunistic pathogens in people, their ecological niches and significance beyond the clinical setting are unclear. However, evidence is emerging that transmission can occur between the three One-Health compartments of the human population, animal population and the environment. Using a One-Health approach, the presence of World Health Organization Saccharomycotina priority pathogens in these different niches is reviewed, including evaluation of evidence for genetic similarities between isolates from different ecological backgrounds. The Saccharomycotina yeasts that colonise healthy humans vary by anatomical site, age, ethnicity and geographic region. These same species of yeasts, including those of medical importance, colonise a diversity of vertebrate hosts, especially birds. Shorebirds, such as gulls, that feed on human refuse in urban environments can be carriers, reservoirs and disseminators of azole resistant isolates of yeasts including Candida tropicalis, C. parapsilosis and Nakaseomyces glabratus likely of anthropogenic origin. Saccharomycotina yeasts are also abundant in natural and built environments. Multilocus sequence typing (MLST) and other methods of genotyping combined with population analyses of C. albicans and non- albicans yeasts have revealed that human clinical isolates have some degree of separation from, but also significantly overlap with, animal and environmental isolates, supporting transboundary transmission. In conclusion, transmission of Saccharomycotina yeasts can occur between these niches. Further research into the directionality and risk of inter-niche transmission using a coordinated One Health approach is required.