Health officials have recently released a study that salmon caught here in North America are sometimes contaminated with tapeworm larvae. Specifically looking at salmon caught in Alaska, researchers have been able to find a specific tapeworm, known as Diphyllobothrium nihonkaiense in raw salmon. More commonly known as the Japanese broad tapeworm, it is the second most common cause of diphyllobrothriosis across the world. There have been about 2000 cases of illness reported, and most of these illnesses were located in northeastern Asia. However, it is possible that the amount of illnesses that have been reported may be underestimated. The Japanese broad tapeworm was first separated from other tapeworm species in 1986, due to its different genetic makeup. The Japanese tapeworm has been identified as the contaminant for several different types of salmon, including chum salmon, masu salmon, pink salmon, and sockeye salmon. Contaminated salmon has been found in Russia, Japan, the United States,and South Korea. Thus, health officials have warned consumers that salmon from the American and Asian Pacific coasts may be contaminated with the Japanese broad tapeworm. The study took a look at a total of 64 wild salmon, spread across 5 species. There was 1 chinook salmon, 1 coho salmon, 23 pink salmon, 8 rainbow trout, and 31 sockeye salmon. Larva was found in one of the samples, from Resurrection Creek. The samples of larvae taken from these salmon, which were usually found near the spinal cord of the fish, were tested in a laboratory. It was discovered that these larvae were a near perfect match to Japanese broad tapeworm.
Although tapeworm infections have not been closely watched in the Pacific Northwest, because of molecular testing it appears that illnesses have been occurring since 2008. There are a few factors responsible for this rise in tapeworm cases in humans. First and foremost, the amount of raw fish being consumed is exponentially rising, due to the popularity of sushi. Researchers have concluded that this is probably the source of tapeworm cases in places where they are uncommon. Also, the way that these salmon are transported does not prevent contamination. Salmon from the Pacific Ocean are usually transported unfrozen, but on ice. This method of shipping does not eliminate tapeworm larva, though, so the larva can survive to cause illness in areas where it is not common, like China, Europe, New Zealand, and the United States.
Raw fish has caused foodborne illness outbreaks in the past. Most recently, raw scallops imported from the Philippines, and sold at Genki Sushi, caused a major outbreak of Hepatitis A. This outbreak began in mid June 2016, and continued to infect people until October 2016. The final update for that outbreak was not until early January 2017. Nearly 300 people were sickened in that outbreak, most of whom were from the Hawaiian island of Oahu. Many people from the other islands reported illness, as well as 7 people from the contiguous United States. The contaminated scallops were able to be embargoed and held at warehouses, helping to reduce the chance of further infection. In 2015, frozen raw tuna was the cause of a Salmonella outbreak. This multistate outbreak was investigated by the CDC, who found that there had been 65 people sickened in 11 different states. Eleven people were hospitalized because of their illnesses. The majority of people interviewed said that they had eaten raw tuna sushi prior to being sick.
The CDC has warned that anyone who has certain risk factors, including those over the age of 65, pregnant women, people with weakened or suppressed immune systems, and those under the age of 5 should not consume any raw fish or shellfish. Foodborne illnesses can be much worse in members of these groups, so it is important for them to avoid raw seafood even when there is no ongoing outbreak. Thankfully, most pathogens, including tapeworms, can be eliminated from any food items by thoroughly cooking food items. The FDA recommends that most seafood needs to be cooked to an internal temperature of 145 degrees fahrenheit. In the event that a food thermometer is unavailable, fish should be cooked until the flesh is opaque and easily separated by fork. In the case of shrimp and lobsters, their flesh will turn pearly and opaque when they are done cooking. Scallops will become firm, as well as turn opaque. Lastly clams, mussels, and oysters will open their shells during cooking. The FDA states that an ammonia odor will be present with spoiled seafood. This odor will get worse if the seafood is cooked. Seafood should never be left out of the refrigerator for more than 2 hours. Pathogens can also be eliminated by freezing food items. Although this may not kill hardy bacteria such as Listeria monocytogenes, other bacteria, viruses, and tapeworms can be killed by freezing temperatures. Because some pathogens can still survive, thorough cooking is considered to be the best way to prevent infection.
The Japanese broad tapeworm, Diphyllobothrium nihonkaiense, is a member of the Diphyllobothrium family of tapeworms. The most common species of this family is Diphyllobothrium latum, but there are several different species of broad tapeworm. Tapeworms from this family are some of the largest tapeworms to infect humans, and can grow to be up to 30 feet long. Most cases of illness caused by these tapeworms tend to come from contaminated freshwater fish, including perch, salmon, walleye pike, trout, and others. Diphyllobothrium infections usually occur in the northern hemisphere, although cases of illness have been reported in Chile and Uganda. Unfortunately, most cases of Diphyllobothrium infection are asymptomatic, meaning that the symptoms of infections will not be easily seen. If symptoms appear, however, they will likely include abdominal pain, diarrhea, vomiting, anemia because of vitamin B12 deficiency, and weight loss. In serious cases, intestinal obstruction or gallbladder disease may occur. A tapeworm infection is usually diagnosed through the testing of a stool sample for tapeworm eggs. Once a diagnosis is made, there are several medications that a doctor may prescribe to treat the infection. If you or a loved one begins to show the symptoms of a Diphyllobothrium infection, contact a medical professional.