Dogs are infected by eating raw fish containing the infective pleurocercoids.
Although worldwide in distribution, the original heartland of Diphyllobothrium spp spreads across Scandinavia, northern Russia, and western Serbia.
The life cycle invovles both a paratenic and intermediate host. Eggs are shed in dog feces and hatch in water releasing a ciliated, free-swimming coracidium.
A copepod ingests the coracidium and it develops into a procercoid in the body cavity. When a fish ingests the infected copepod, the procercoid will migrate to the muscles or viscera and develop to the pleurocercoid stage. If the second intermediate host is eaten by another fish the pleurocercoid will migrate to the muscles or viscera of the new (paratenic) host. When the host containing the pleurocercoid is ingested by a definitive host the worm attaches to the small intestine wall and begins to develop proglottids. The prepatent period is 3 to 4 weeks. Eggs are released from the gravid proglottids and pass out in the feces.
Dogs are usually asymptomatically infected, although polyphagia and weight loss are commonly observed in urban and wild dogs with heavy burdens.
In humans may cause pernicious anemia due to vitamin B12 uptake by the worm.
Treatment is usually effective with praziquantel given orally as a single treatment.
- Schurer JM et al (2012) Sentinel surveillance for zoonotic parasites in companion animals in indigenous communities of Saskatchewan. Am J Trop Med Hyg 87(3):495-498
- Ramana K et al (2011) Diphyllobothriasis in a nine-year-old child in India: a case report. J Med Case Rep 5:332
- Merck Veterinary Manual