Anisakiasis is a parasitic disease of the digestive system caused by nematode worms. This infection is contracted when an individual consumes raw or undercooked seafood containing larvae from the Anisakis genus. The parasite’s temporary presence can provoke a significant reaction from the body. The prevalence of this condition is highest in regions where dishes featuring raw fish are common dietary staples.
Cause and Transmission
The life cycle of the Anisakis parasite begins in the stomachs of marine mammals like whales, dolphins, and seals. These mammals excrete the parasite’s eggs into the ocean. Once in the water, the eggs hatch into larvae that are subsequently consumed by small crustaceans, such as krill. These infected crustaceans are then eaten by larger fish and squid, which in turn become intermediate hosts for the larvae.
Humans become accidental hosts by consuming raw or improperly prepared marine fish or squid containing these larvae. The infection is not transmissible from one person to another. Dishes that commonly pose a risk include sushi and sashimi, as well as cured or marinated items like lomi lomi salmon, pickled herring, and ceviche.
Symptoms and Diagnosis
Symptoms of anisakiasis manifest within hours of consuming the contaminated seafood. The initial signs include intense abdominal pain, nausea, and vomiting. Some individuals may feel a tingling sensation in their throat or mouth while eating, which is the physical movement of the worm. This can sometimes lead to the worm being coughed up or manually removed, preventing a full infection.
The infection can be categorized based on where the worm attaches within the gastrointestinal tract. Gastric anisakiasis occurs when the larva burrows into the stomach wall, while intestinal anisakiasis involves the small intestine. Intestinal cases may develop more slowly, with symptoms resembling those of appendicitis or Crohn’s disease appearing one to two weeks later. Additionally, some people experience allergic reactions to the parasite, ranging from mild hives to severe, life-threatening anaphylaxis.
Diagnosing anisakiasis is most reliably achieved through an upper endoscopy. This medical procedure involves inserting a thin, flexible tube with a camera into the esophagus, stomach, and small intestine. This allows a physician to directly visualize the worm, which is typically about two centimeters long, and confirm its presence.
Medical Interventions
The most effective treatment for anisakiasis is the physical removal of the parasite. During the diagnostic endoscopy, the physician can use forceps passed through the endoscope to grasp and extract the larva from the gastrointestinal lining. Since the majority of symptoms result from the body’s inflammatory response to the worm, its removal usually leads to a rapid resolution of symptoms.
Most infections resolve on their own over several days or weeks as the parasite cannot survive in a human host and eventually dies. In situations where the worm is not removed, anti-parasitic medications, such as albendazole, may be prescribed. The effectiveness of these drugs can be inconsistent. In uncommon instances where the worm causes a bowel obstruction or perforation, surgical intervention may be required.
Prevention Methods
Avoiding infection depends on properly handling and preparing seafood. The two most reliable methods for destroying Anisakis larvae are cooking and freezing. The U.S. Food and Drug Administration (FDA) advises cooking seafood to an internal temperature of at least 145°F (63°C).
For those who enjoy raw or undercooked fish, freezing is an effective preventative measure. The FDA’s guidelines recommend freezing fish to -4°F (-20°C) or below for a minimum of seven days, or to -31°F (-35°C) or below until solid and then storing for at least 15 hours. While the term “sushi-grade” often implies that the fish has been frozen to these standards, it is a commercial descriptor rather than a regulated one. Careful sourcing is still important.