Giardia duodenalis Colonization Slightly Affects Gut Microbiota and Hematological Parameters in Clinically Healthy Dogs

SIMPLE SUMMARY: Giardia is a worldwide cause of acute diarrheal disease both in humans and animals. Domestic dogs may be either asymptomatic or may show clinical signs. Here, we report a study comparing two groups of clinically healthy German shepherd dogs differing for G. duodenalis colonization. Gut microbiota and the hematological, biochemical, and fecal parameters related to intestinal function were investigated. The results display a scenario in which G. duodenalis exerts an effect upon the gut microbiota affecting the proportion of a few bacterial taxa known to be associated with improved lipids metabolism and protection from gut inflammation. This also suggests that the antiparasitic treatments that are usually administered to G. duodenalis-positive dogs might be avoided in clinically healthy subjects since the presence of G. duodenalis does not substantially modify the microbial ecology of the intestinal lumen nor the hematological markers of disease. ABSTRACT: 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.