HEALTH NEWS

Warning About New Parasite in Raw Seafood

Written by Elizabeth Pratt on May 25, 2017

sushi

You may want to think twice before eating sushi and other raw seafood.

Doctors are warning that with the rise in popularity of sushi in the Western world, there has been a rise in a parasitic infection known as anisakiasis.

According to the U.S. Centers for Disease Control and Prevention (CDC), anisakiasis can occur when fish or squid containing the infected larvae is eaten raw.  

The worms in the infected food can then invade the stomach wall or intestine.

Symptoms of the disease include abdominal pain, nausea, diarrhea, vomiting, abdominal distention, blood and mucus in the stool, and a mild fever.

In a report recently published in BMJ Case Reports, Dr. Joana Carmo and colleagues described the case of a previously healthy 32-year-old man who started to experience stomach pain, low grade fever, and vomiting.

“After a careful interview, he revealed that he recently ate sushi. An upper gastrointestinal endoscopy was performed, and showed on the gastric body, a filiform parasite,” they wrote.

The larva was removed and the patient’s health improved immediately.

Most cases of anisakiasis occur in Japan, where sushi is commonly eaten, but cases of the parasite have been increasingly reported in Western countries.

Read more: Get the facts on food poisoning »

Is it safe to eat raw fish?

Lauri Wright, PhD, assistant professor in public health at the University of South Florida, and a spokesperson for the Academy of Nutrition and Dietetics, said it’s best to avoid raw fish.

“Raw fish does not provide any additional health benefits over cooked fish, so it is not worth the risk of contaminants or foodborne illness to consume raw,” she told Healthline.

In particular, Wright said, those at high-risk for foodborne illness could suffer severe and life-threatening illness from consuming raw or undercooked fish or shellfish.

“These individuals include those with compromised immune systems or with decreased stomach acidity, as well as pregnant women, infants, young children, and older adults. Raw fish and shellfish consumption is never advised for high-risk individuals. If you're in this category, thoroughly cook fish and shellfish,” she said.

Katie Ferraro, a registered dietitian, and assistant clinical professor at the University of San Diego and the University of California San Francisco, holds a similar view.

“If you look at different types of foodborne illness, one of the common threads is that raw and undercooked fish and shellfish are often the culprits. Not to say that there aren’t very safe versions of these foods, but for high risk populations … it is wise to avoid these foods,” she told Healthline.

Read more: The worst foodborne illness outbreaks in recent US history »

More than parasites

Wright says it’s not just parasitic infections like anisakiasis that people should be concerned about. Other foodborne illness from eating raw or undercooked seafood poses a significant hazard.

“Major types of food poisoning that can result from eating raw or undercooked fish and shellfish include salmonella and Vibrio vulnificus. For raw shellfish connoisseurs, especially raw oyster lovers, you specifically need to know about the risk for V. vibrio infections. V. vulnificus is a bacterium that lives in warm seawater and is not caused by pollution,” she explained.

Despite popular myth, Wright said neither hot sauce nor alcohol will kill bacteria and protect you from food poisoning.

“The best rule of thumb is to follow good food safety practices and properly cook all seafood,” she said. “One other safety tip of interest: If you do decide to eat raw fish, choose fish that has been previously frozen. That's because freezing will kill any potential parasites present.”

But freezing won’t protect you from everything.

“Unfortunately, freezing doesn't kill every harmful organism,” she said.

Read more: Best types of fish to eat »

Tips on cooking, storing fish

Both Ferraro and Wright suggested that fish and shellfish can provide valuable nutrients and are good sources of protein, vitamins, and minerals.

These foods are also rich in omega-3 fatty acids, and can help in the reduction of common diseases.

Both suggested it is best to stick to fish and shellfish in cooked varieties, to obtain the benefits without the risk of infection.  

Wright said there are some easy ways to avoid foodborne illness and infections from fish and seafood.

At the market, buy fish that is properly refrigerated below 40°F (4°C) or well-packed with ice, and look for fish with shiny, firm flesh that doesn’t have a strong “fishy” odor.

In your fridge, keep fresh fish in airtight containers or well-wrapped for no more than two days. Store fresh, pasteurized, or smoked seafood between 32°F (0°C) and 38°F (4°C), and store live shellfish in well-ventilated containers.

During preparation, keep raw and cooked seafood separate, including using separate chopping boards. Hands, cuttings boards, plates, and utensils should be thoroughly cleaned between holding raw seafood and food that is ready to eat.  

As for eating out, if you really want to eat sushi or raw seafood, Wright recommended taking sensible precautions.

“There are a plethora of well-liked raw and undercooked fish and shellfish items on menus today. For healthy individuals, these foods can generally be consumed safely when they're from reputable restaurants or markets that use fresh, high-quality ingredients and follow proper food safety practices,” she said.

But she emphasized the risks of eating raw fish and seafood far outweigh the benefits.

“There are no health benefits of consuming raw fish or sushi over cooked fish. Therefore, we do not recommend consuming sushi or any raw fish/seafood,” she said.

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