Capnocytophaga canimorsus is a fastidious, capnophilic, fusiform, and filamentous gram-negative rod. It is part of the normal oral flora of dogs and cats and can cause an infection in humans, but is of generally low virulence in healthy individuals. A case of fatal sepsis due to Capnocytophaga canimorsus in a 46-year-old woman with clinically silent cystic echinococcosis discovered postmortem is present. She had been bitten by a dog 3 days before the symptoms appeared. The family had owned the dog for 4 years. A preliminary diagnosis of septic shock of unknown etiology with multisystem organ failure was established. Despite all the efforts, the patient died on the seventh day of hospitalization. Laboratory findings received postmortem showed Capnocytophaga canimorsus isolated from the blood culture after 7 incubation days. Autopsy showed a cyst in the liver with a fibrotic wall and necrotic eosinophilic interiors containing fragments of Echinococcus granulosus scolices. In conclusion, an interaction possibly established long ago between the host and Echinococcus granulosus conditioned immunosuppression mechanisms developed by the parasite in this case, which can explain such an aggressive course of the infection with Capnocytophaga. Two dog-related infections were fatal in the middle-aged dog owner considered healthy before this hospitalization. Vigilance concerning recent exposure to dogs or cats and potential immunosuppression risk factors must be maintained in a patient presenting with clinical features of fulminant sepsis.