Ecology and sources of yeast infection
Yeasts can be found in plants, soil, air, aquatic environment, in invertebrate and vertebrate animals, that is, in almost all ecosystems. These microorganisms can be in their symbiotic state, in mutualism, or in parasitism.
In humans, several species can be part of their natural microbiota, in the gastrointestinal tract, in mucocutaneous tissues and skin. In man, a large part of yeast infections, especially of the genus Candida, are of endogenous origin and are linked to risk factors such as old age, prematurity, avitaminosis, antibiotic therapy, cancer, and other diseases that cause immunodepression of the host [7].Extrinsic factors can also be important, such as the rupture of the natural barrier of the skin and mucous membranes, the use of invasive hospital material and contact with contaminated ecological niches. Direct transmission between people can occur in sexual relations [8].
In dogs, the main yeast found on the skin and mucocutaneous surfaces is Malassezia pachydermatis, which easily recovers in the folds of the skin and especially in the various parts of the ear. The prevalence of some types of yeasts in the oral mucosa of dogs is related to several habits, such as licking, sniffing and exploring environments.
The licking of the paws and other areas of the body explains the considerable presence of Malassezia pachydermatis in the oral cavity of dogs. Considered a saprophyte in the skin of dogs, this microorganism can cause dermatitis in several situations, and in these cases, there is also an increase in its presence in the oral mucosa. Other relevant yeasts of these animals belong to the genera Candida, Rhodotorula and Trichosporon, which are, in most cases, in balance with the dogs’ organism [9].
It is also reported that Cyniclomycesguttulatus, present in the stomach, intestine and feces, which in situations of imbalance with the commensal microbiota, may be related to clinical conditions that affect the gastrointestinal tract [10].
The habit of sniffing the soil, in parks and gardens, hunting in forests and dens, favors the sharing of microorganisms among animals linked to these environments. The organic matter present in these places, mainly in the feces of birds and bats, favors colonization by fungi such as Cryptococcus spp. and Histoplasma capsulatum, which in situations favorable to microorganisms (host immunosuppression; high microbial inoculum load) can cause serious diseases [11].
Advances in veterinary hospital techniques, especially surgical procedures and hospitalizations, also brings new sources of infection for dogs. The ability of microorganisms of the genera Candida and Malassezia to form biofilms makes equipment such as specula, probes and other surgical materials possible sources of transmission of these microorganisms. For this reason, the correct asepsis and sterilization for handling this equipment is extremely important to avoid mycoses and severe cases of fungemia [12].
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