A Fishy Tale of Macrocytosis

Abstract

Diphyllobothriasis is a rare fish tapeworm infection, yet one of the most important fish-borne human diseases due to the high morbidity and commonly missed diagnosis. It occurs by ingesting infected uncooked fish. Several fish tapeworm species can affect humans, with the most prevalent of these being Diphyllobothrium latum found in pike, perch, and arctic char. In humans, the worm attaches to the small bowel where it can live undetected for 10 to 15 years and can grow as long as 15 meters. While in the small bowel, it competes with the host for vitamin B12, leading to vitamin B12 deficiency and macrocytosis. The signs and symptoms of infestation are often vague and non-specific, making for a challenging diagnosis. Furthermore, physical examination and laboratory investigations are typically unremarkable. We describe only the fourth case report of D. latum in Canada. It occurred in an otherwise healthy patient with a two-year history of vague abdominal pain, diarrhea, low B12, and macrocytosis. The patient was an avid sushi eater and remained symptomatic and undiagnosed during this time. Spontaneous passage of the worm and treatment with praziquantel ultimately led to resolution of her symptoms.