Mesocestoides vogae Infection in Dogs: Confusion with Echinococcosis.

We describe six independent cases of Mesocestoides infection in dogs presenting with diarrhea. Between November 2022 and August 2024, we were contacted by veterinarians regarding the identification of a species of small tapeworm excreted in dog feces. The veterinarians suspected the organism was Echinococcus multilocularis and believed it should be reported to health centers as a notifiable disease. Segmented and unsegmented worms, approximately 600 to 1,400 µm in length, were recovered from fecal samples. Microscopically, the worms had four suckers on the scolex but no rostellum. Subsequent molecular analysis of the mitochondrial cox1 and 12S rDNA genes revealed that all cases involved Mesocestoides vogae. The affected dogs were treated with an anthelmintic, and the diarrhea disappeared immediately. Possibly owing to the heavy infection load, the host animals had developed diarrhea, with the parasite likely expelled before reaching maturity. These small tapeworms with few proglottids could, therefore, confuse veterinarians.