Study by Calgary doctors warns home cooks about parasites in raw fish

Calgary doctors say a rare parasite could become more common as uncooked culinary trends such as sushi, sashimi and ceviche grow in popularity. A new report in the Canadian Journal of Infectious Diseases and Medical Microbiology examines the case of a Calgary man stricken by tiny parasitic worms in his stomach after eating raw, wild salmon from a grocery store.

Calgary doctors say a rare parasite could become more common as uncooked culinary trends such as sushi, sashimi and ceviche grow in popularity.

A new report in the Canadian Journal of Infectious Diseases and Medical Microbiology examines the case of a Calgary man stricken by tiny parasitic worms in his stomach after eating raw, wild salmon from a grocery store.

The article says it’s the first time the tiny, toothed worms have been found in a human after consuming Canadian store-bought salmon.

Dr. Stephen Vaughan from Calgary’s South Health Campus led the study and reported the results.

The report says the 50-year-old man arrived in the emergency department with vomiting and upper abdomen pain about one hour after eating raw, wild salmon.

After x-rays and stool tests found nothing remarkable, doctors sent an endoscope camera inside the patient’s stomach and spotted the worms — between one and two centimetres long — wriggling inside several stomach ulcers.

Two worms were removed and identified as anisakis, a parasitic worm that lives in fish and aquatic animals and leads to the condition anisakiasis.

“Although a skilled sushi chef will recognize the distinctive `watch coil’ appearance of the larval worms (approximately 1 centimetres to 2 centimetres) in raw fish, individuals preparing their own sushi may not,” the report’s authors wrote.

Researchers say that raw fish prepared at home can contain anisakis and other dangerous parasites because the fish may not have been frozen — a process typically used by sushi restaurants that kills the tiny larvae.

Several provinces have regulations that ensure that raw fish is frozen before being served at restaurants, but grocery stores are often not included in such regulations.

To err on the side of caution, the report recommends that fish purchased from grocery stores be frozen at -20 C for a week — or at a colder temperature for a shorter period of time — before being eaten raw.

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