If your dog's intestines contain the yeast Cyniclomyces guttulatus -- also known as Saccharomycopsis guttulatus -- it's generally not a problem. However, if your dog suffers from chronic diarrhea, it's possible that Cyniclomyces guttulatus is the culprit. It may not be the most common reason for long-term loose bowels, but it's something your veterinarian should consider if testing for other causes comes up negative.
Scientists don't all agree on whether Cyniclomyces guttulatus is always harmless in canine intestines. A minority of researchers consider the yeast pathogenic, or capable of causing disease. In rabbits, Cyniclomyces guttulatus lives in the intestines and stomachs, but in dogs it is the bile ducts, along with the intestines. As long as the yeast causes the dog no harm, it isn't considered a parasite in veterinary terms.
Means of Transmission
Since Cyniclomyces guttulatus is commonly found in the intestines of rabbits and rodents, the primary means of its transmission into a dog's intestines is via consumption of such carcasses or their feces.
A study by researchers at the University of Utrecht in the Netherlands, published in Volume 172 of the journal "Veterinary Microbiology," sampled the numbers of Cyniclomyces guttulatus in the fecal samples of healthy dogs and those with chronic diarrhea and found no "clinical significance." After the initial study, 57 dogs suffering from chronic diarrhea and with large amounts of Cyniclomyces guttulatus in their feces were treated because nothing else in the various tests gave any indication of a reason for their chronic diarrhea. Thirty-six dogs did not respond when given the antifungal antibiotic nystatin, although the yeast was no longer shed in their feces. For 13 dogs, the diarrhea ceased for more than two weeks, with no yeast in the feces. However, 11 of these dogs suffered a relapse of chronic diarrhea, with most of them no longer shedding the yeast. The study concludes that in a very few cases, Cyniclomyces guttulatus could cause chronic diarrhea. (ref 1)
A 2011-2012 study conducted in an emergency veterinary hospital in a suburb of Rio de Janeiro represented the initial isolation of Cyniclomyces guttulatus in canines suffering from chronic gastrointestinal issues in the Southern Hemisphere. Like the Dutch study, the Brazilian study concludes that the yeast was not a major factor in canine chronic diarrhea, and that "the association between Cyniclomyces guttulatus and gastrointestinal disturbances in dogs most likely reflects a breakdown in the innate defense mechanisms of the host." (ref 2)
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