Diphyllobothriasis: fish tapeworm disease in the circumpolar north

Although fish tapeworm infections in arctic and subarctic residents are often attributed to the cestode Diphyllobothrium latum, other Diphyllobothrium species are frequently responsible. D. dendriticum, for example, occurs throughout the circumpolar area at high latitudes beyond the range of D. latum. Several additional species are also implicated in human infections in northern communities bordering the Pacific: D. ursi from northern Canada and Alaska, D. dalliae from Alaska and Siberia, and D. klebanovskii from Siberia. Routine diagnosis of diphyllobothriasis by coprology does not allow designation of the Diphyllobothrium species involved as their eggs cannot be differentiated and identification of the proglottids from adult worms requires a taxonomic specialist. On the other hand, relevant information on the Diphyllobothrium species most likely to infect the inhabitants of a particular region can be derived from a knowledge of the fish consumed. Larvae of D. dendriticum occur predominantly in salmonid fishes (e.g. arctic char, salmon, trout, whitefish), and this parasite has never been found in pike and perch, the usual intermediate hosts of D. latum. Conversely, D. latum is rarely found in salmonids. D. ursi and D. klebanovskii predominantly occur in Pacific salmon, and D. dalliae in Alaskan blackfish. Species other than D. latum probably constitute transitory intestinal infections in humans, usually lasting for only a few months. Although many carriers are asymptomatic, overt clinical manifestations of diphyllobothriasis can include diarrhea, epigastric pain, nausea and vomiting. There are no reports of anaemia associated with any of the northern species except D. latum. Effective control for diphyllobothriasis originating from D. latum has been achieved in many areas by a combination of selective drug therapy and improved sewage treatment.(ABSTRACT TRUNCATED AT 250 WORDS)