(CNN) — Anisakiasis, an illness caused by eating parasite-contaminated fish or seafood, is on the rise in Western countries where eating sushi and other raw or undercooked fish and seafood dishes has gained popularity, according to a report published Thursday in BMJ Case Reports.
The authors draw a portrait of the illness from the experience of a previously healthy 32-year-old man who developed severe upper gut pain, vomiting and fever that lasted a week before he entered the hospital.
Dr. Joana Carmo, lead author and a physician in the gastroenterology department of the Hospital of Egas Moniz in Lisbon, Portugal, and her co-authors say a physical examination indicated tenderness in the abdomen, while the lab results showed an increase in white blood cells, which is a typical sign of infection.
During an interview, the man said he had recently eaten sushi.
Based on this dietary information, his doctors performed an upper gastrointestinal endoscopy: a non-surgical examination of the digestive tract, using a flexible tube with a light and camera on the end. This inner vision revealed a swollen intestinal membrane with a firmly attached parasite, its end penetrating the stomach.
The first case of human infection with anisakiasis was described by scientists in the Netherlands during the 1960s. Because this first record occurred after the patient had consumed some lightly salted herring, the infection was originally referred to as “herring worm disease.”
Since then, cases have appeared in many other countries, though “mainly in Japan because of the frequent ingestion of raw fish,” Carmo said.
Although the anisakis parasite can live as a larva for several weeks in a human stomach, it will die before developing into an adult. But before it dies, it produces an inflamed mass in the esophagus, stomach or intestine.
Untreated gastric disease can lead to chronic, ulcer-like symptoms lasting for weeks to months, Bao said.
Though treatment is not always necessary, removal by endoscopy may be necessary to alleviate symptoms. No specific drug has been identified to kill the live parasites, Bao said, adding that “surgical removal is occasionally required.”
There are other ways of getting rid of the worm.
“Some people experience a tingling sensation after or while eating raw or undercooked fish or squid. This is actually the worm moving in the mouth or throat,” reads the CDC website. In such cases, it is possible to cough up the worm or remove it by hand. Sometimes, vomiting expels the worm.
To help reduce the risk of illness caused by eating fish or squid, the Food and Drug Administration has food safety programs and hazard reduction procedures (PDF) that distributors of fish and squid are expected to follow.
“For example, freezing fish to the appropriate temperature and for the appropriate duration can kill parasites,” Rowland said. The European Union follows similar practices, according to Carmo.
Along with avoiding raw fish, the CDC recommends that seafood be cooked to an internal temperature of at least 145° F (about 63° C). Carmo said freezing to minus-20 degrees Celsius for a minimum of 72 hours also kills the parasite.
Some people, though, will never give up eating their beloved sushi or other raw fish delights.
“Properly trained sushi chefs can detect anisakis larvae,” Carmo said. “They are grossly visible in the fish.”