Not all acute reactions after eating seafood are allergic. In fact, there are three common syndromes that are allergy-mimics, but are non-allergic: Scramboid, Ciguatera and Anisakis.
Ciguatera fish poisoning (CFP) is the most common with an estimated half-million people affected yearly. CFP is caused by the ingestion of toxins that invade tropical and subtropical fish, especially in the Pacific and Caribbean. More than 400 species of fish are known to carry this toxic organism. Because of global warming and international food commerce, the toxin is going to become a more frequent problem. Also, affected fish appear normal in appearance and taste, and the toxin is not inactivated by cooking. The symptoms that occur are intense pruritis (itchiness), followed by nausea, vomiting and diarrhea. In severe cases blood pressure and pulse can drop, leading to fainting and loss of consciousness.
Scromboid toxicity occurs from fish that have a high innate histidine content, such as tuna and mackerel. Histidine is readily converted to histamine once the fish is digested and this sudden load of histamine accounts for the symptoms of flushing, hives, respiratory symptoms and nausea and vomiting. The implicated fish are typically “past prime,” and the histidine is high because the fish is decomposing. Also, this “old fish” contains two other bio-active amines that can add to the histidine effect: putrecine and cadaverine.
Anisakis is a nematode worm found in many fish. This syndrome is actually a true allergy, but to the worm and not to the fish. The problem only occurs for people who eat raw or lightly cooked fish. Symptoms include wheezing, hives, generalized itching and nausea and vomiting.
Treatment for Ciguatera is primarily in the form of hydration – by mouth or IV – if nauseous. For Scramboid and Anisakis, it’s antihistamines and hydration.
Prevention? For Scramboid, ensure the freshness of tuna or mackerel. For Anisakis, cook the fish. An antibody test kit for Ciguatera is being developed so one can test fish purchased at a market or restaurant before eating it.