Infection with which organism may result in vitamin B12 deficiency and megaloblastic anemia?

• A. Diphyllobothrium latum
• B. Hookworm
• C. Hymenolepis diminuta
• D. Taenia saginata

Answer: (D)

Vitamin B12 deficiency with megaloblastic anemia occurs when a parasite steals or blocks the host’s available B12 in the gut. Diphyllobothrium latum, the fish tapeworm, lives in the small intestine and has a high affinity for vitamin B12, taking it up from the lumen. This depletes the host’s B12 supply, impairing DNA synthesis in hematopoietic cells and leading to ineffective erythropoiesis with macrocytic (megaloblastic) anemia. Clinically, this can present with fatigue, pallor, and glossitis, along with a high mean corpuscular volume and hypersegmented neutrophils on blood smear.

The other organisms listed do not typically cause this deficiency: hookworms cause iron-deficiency anemia from chronic blood loss; Hymenolepis diminuta is usually asymptomatic in humans; Taenia saginata does not cause B12 deficiency.