Giardia duodenalis (Giardia) is a worldwide cause of acute diarrheal disease both in humans and animals. The primary aim of this study was to investigate possible variations in gut microbiota in a population of asymptomatic dogs (n = 31), naturally infected or not by Giardia. Gut microbiota and the hematological, biochemical, and fecal parameters related to intestinal function were investigated. Giardia infection was associated with a significant shift of beta diversity, showing a relevant reduction of Gammaproteobacteria and an increase of Fusobacteria in male-positive dogs if compared with negatives. A significant imbalance of different bacterial taxa, with particular reference to the Erysipelotrichales, Lactobacillales, Clostridiales, and Burkholderiales orders, was observed, with the first two being higher in Giardia-positive dogs. Giardia-positive males displayed significantly higher values of cCRP than negative males as well as positive females, supporting the presence of a pro-inflammatory state. Taken together, these results indicate that the presence of Giardia does not substantially modify the microbial ecology of the intestine nor the hematological markers of disease. Thus treatments against Giardia should be considered with caution in asymptomatic subjects.
