Food Safety Helps Avoid Tapeworm

May 26, 2018 GMT

Q: I read a few years ago that someone wound up with tapeworms after eating raw fish, and now it has apparently happened again. What’s the deal?

A: Because we’re familiar with both incidents you’re referring to, we think it’s a good idea to start by letting any sensitive readers know that we’ll be discussing worms and intestines, with details that may be unsettling.

Six years ago, a Japanese man who frequently ate raw salmon became ill with stomach pains and watery diarrhea. According to an account published in the journal BMJ Case Reports, infectious disease specialists examined the contents of the man’s stool and found Diphyllobothrium nihonkaiense, commonly known as the Japanese broad or fish tapeworm. (And yes, we had to look up the spelling.) It was close to 40 inches long,

Earlier this year, during an episode of a medical podcast, an emergency room physician from Fresno, California, described a similar incident. A patient went to the hospital after he pulled a 5-foot-long worm out of his body during an episode of bloody diarrhea. The man then wrapped the worm around a toilet paper roll and headed for the ER, where he presented the worm to the doctor. As with the Japanese man, it turned out that the California man frequently ate raw salmon. In fact, he ate it every day. Although it was impossible to be certain, doctors involved with the case suspected that the raw salmon was the source of the tapeworm infection.


Cases like this are rare, but the truth is that any time you eat raw or undercooked meat, you run the risk of ingesting whatever parasites may have been present in the fish or animal. These range from minute, single-celled organisms that can be seen only with a microscope to the worms whose unnerving size help these stories of infection go viral. In the case of the Japanese broad tapeworm, it had been believed that it was limited to areas of Asia. But according to a report from the Centers for Disease Control and Prevention published last year, it has now been identified in wild salmon caught in Alaska.

Symptoms of infection include the pain and diarrhea that both of the men reported. Diagnosis is made by a microscopic examination of the patient’s stool for eggs, or for segments of the tapeworm itself.

The good news is that a tapeworm infection can be successfully treated with several safe, effective drugs.

So how do you avoid tapeworm infection in the first place? The easiest and most effective way is to never eat raw or undercooked fish. The CDC wants you to cook your fish to an internal temperature of at least 145 degrees. Freezing fish at minus 4 degrees or lower for seven days or at minus 31 or lower until solid will also kill any parasites.

ASK THE DOCTORS is written by Robert Ashley, M.D., Eve Glazier, M.D., and Elizabeth Ko, M.D. Send questions to askthedoctors@, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095.