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 (R (2) = .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.