Eating raw fish raises potential health concerns

Two case studies from Japan presented at the 72nd Annual Meeting of the American College of Gastroenterology point to a potential health problem in the United States, as more Americans consume raw fish in the form of sushi and sashimi. Anisakiasis (round worm) is a human parasitic infection caused by the consumption of raw or undercooked seafood containing Anisakis larvae.

Consumers should be aware that while larvae for the parasitic worm Anisakis cannot survive in a human host, the ingested larvae can produce severe intestinal problems warranting a visit to the emergency room.

When ingested by humans, the larvae attach themselves to the tissues lining the stomach and intestines, resulting in sudden abdominal pain, nausea, vomiting, and diarrhea. Since the larvae cannot survive in humans and eventually die, intestinal anisakiasis usually resolves on its own.

Researchers in Japan examined two cases of intestinal anisakiasis presenting as an obstruction of the small intestine. In each case, both patients, ages 64 and 70, were rushed to the emergency room with sudden abdominal pain and vomiting after eating raw sardines as sashimi two days earlier. The diagnosis of anisakiasis in the stomach can easily be confirmed by endoscopy. However, small intestinal anisakiasis is difficult to diagnose. Both patients had abdominal X-rays showed air-fluid levels suggesting a small intestinal obstruction. Using a multidetector-row computed tomography (MDCT), doctors obtained high quality images of the small bowel, and found the intestinal blockage was caused by the presence of Anisakis larvae. Fluid replacement and resting immediately relieved the patients' symptoms.

Because the symptoms of anisakiasis can mimic other gastrointestinal diseases, it might potentially be misdiagnosed as appendicitis, acute abdomen (peritonitis) or stomach ulcers. According to Mashahiro Matshushita, MD of Haibara General Hospital, “Anisakiasis should be considered in the differential diagnosis of small intestinal obstruction.”