Diphyllobothrium latum infection is associated with which nutritional deficiency, and what is the mechanism?

• A. Vitamin A deficiency due to fat malabsorption
• B. Vitamin B12 deficiency due to competition for B12 absorption
• C. Iron deficiency due to blood loss
• D. Folate deficiency due to intestinal loss

Answer: (D)

Diphyllobothrium latum infection is classically linked to vitamin B12 deficiency because the tapeworm takes up vitamin B12 from the host’s intestinal lumen. As the worm feeds in the small intestine, especially the ileum, it absorbs substantial amounts of the host’s B12, reducing what is available for absorption by the gut lining. Over time, this depletion leads to megaloblastic (macrocytic) anemia due to impaired DNA synthesis in hematopoietic cells, and patients may develop fatigue, pallor, and sometimes neuropathic symptoms. This mechanism—competition for B12 absorption by the parasite—is the key reason B12 deficiency occurs in this infection. Folate deficiency or iron deficiency are not the characteristic findings here; while folate deficiency can cause macrocytosis in other contexts, the hallmark with this tapeworm is B12 depletion from the parasite’s uptake.