Changes in the fecal microbiota in dogs with acute hemorrhagic diarrhea during an outbreak in Norway.

BACKGROUND A severe form of acute hemorrhagic diarrhea syndrome (AHDS) occurred in dogs in the Oslo region of Norway during autumn 2019. OBJECTIVES To characterize the fecal microbiota of dogs with AHDS during the outbreak and compare it to that of healthy dogs from the same period and before the outbreak. ANIMALS Dogs with AHDS (n = 50), dogs with nonhemorrhagic diarrhea (n = 3), and healthy dogs (n = 11) were sampled during the outbreak. In addition, 78 healthy dogs from the same region were sampled before the outbreak between 2017 and 2018. METHODS Retrospective case-control study. The fecal microbiotas were characterized using 16S rRNA gene amplicon sequencing. RESULTS Dogs with AHDS had significantly different microbiota composition (R2  = .07, P < .001) and decreased intestinal diversity relative to healthy dogs from the outbreak period (median, 2.7; range, 0.9-3.5 vs median, 3.2; range, 2.6-4.0; P < .001). The microbiota in dogs with AHDS was characterized by a decrease of Firmicutes and an outgrowth of Proteobacteria, with increased numbers of Clostridium perfringens and Providencia spp. Among the Providencia spp., 1 showed 100% sequence identity with a Providencia alcalifaciens strain that was cultivated and isolated from the same outbreak. No Providencia spp. was found in healthy dogs sampled before the outbreak. CONCLUSIONS AND CLINICAL IMPORTANCE Dogs with AHDS had marked changes in fecal microbiota including increased numbers of Providencia spp. and C. perfringens, which may have contributed to the severity of this illness.