Anisakis is a parasitic roundworm found in marine fish and squids. It can infect humans who consume raw or undercooked seafood. The infection, known as anisakiasis, can lead to gastrointestinal and allergic reactions. It is a global concern, particularly where raw seafood is a common part of the diet.
Anisakis and Transmission
Anisakis nematodes have a complex life cycle involving several hosts. Adult worms live in the stomachs of marine mammals, laying eggs expelled into the water through feces. These eggs hatch into free-swimming larvae, ingested by small crustaceans.
When fish or squid consume these infected crustaceans, the larvae transfer to them, developing into an infective stage within their tissues. Humans become accidental hosts by consuming raw, undercooked, or improperly prepared seafood containing these larvae. Common dishes like sushi, sashimi, ceviche, or lightly cured fish pose a risk. Fish types frequently carrying Anisakis include cod, herring, mackerel, salmon, and squid.
Symptoms and Health Effects
Symptoms of anisakiasis appear within hours to a few days after consuming infected seafood. Gastric anisakiasis, the most common form, presents with sudden, severe abdominal pain, nausea, and vomiting shortly after ingestion. Some individuals might even cough up or expel the larvae.
If the larvae move into the small intestine, symptoms may be delayed, appearing 5 to 7 days later. This intestinal form can cause recurrent abdominal pain, nausea, and vomiting, sometimes mimicking conditions like Crohn’s disease or appendicitis. The larvae can also penetrate the gastrointestinal wall and migrate to other organs, leading to ectopic anisakiasis, affecting areas like the peritoneum or liver. Some individuals may also experience allergic reactions, including hives, skin rashes, breathing problems, or even anaphylaxis, due to the parasite.
Prevention and Safe Seafood Handling
Preventing Anisakis infection depends on proper seafood preparation. Thoroughly cooking seafood is an effective method, as the worms are killed when fish reaches an internal temperature of at least 145°F (63°C).
Freezing seafood is another effective prevention strategy. The U.S. Food and Drug Administration (FDA) recommends freezing fish at -4°F (-20°C) or below for at least 7 days to kill the parasite. For thinner fish, freezing at -31°F (-35°C) for 15 hours can also be effective. Purchasing seafood from reputable sources that adhere to safe handling and freezing guidelines can also reduce the risk of infection.
Seeking Medical Attention and Treatment
If severe gastrointestinal symptoms develop after consuming raw or undercooked seafood, seek medical attention promptly. Symptoms like intense abdominal pain, persistent nausea, or vomiting warrant professional evaluation.
Diagnosis of anisakiasis involves an upper endoscopy, where the worm can be visually identified and removed from the digestive tract. Endoscopic removal of the larvae is curative. While larvae cannot survive long in humans, self-treatment is not effective. Medical intervention ensures proper diagnosis and removal, preventing further complications.