A 43-year-old woman presented to her family physician with a
two-year history of fatigue, diarrhea, and constant dull abdominal
discomfort. Stools were described as normal in frequency and
intermittently loose in consistency. The patient, a marine
biologist with an extensive travel history, noticed that her
symptoms began after a busy year of fieldwork in Iceland, Denmark,
and the Arctic, during which she began regularly consuming raw
sushi and sashimi. Serum vitamin B12 was 157 pmol/ L, compared to a
level...