What are marine toxins?
Marine toxins are naturally occurring chemicals that can contaminate certain seafood. The seafood contaminated with these chemicals frequently looks, smells, and tastes normal. When humans eat such seafood, disease can result.
What sort of diseases do marine toxins cause?
The most common diseases caused by marine toxins in United States in order of incidence are scombrotoxic fish poisoning, ciguatera poisoning, paralytic shellfish poisoning, neurotoxic shellfish poisoning and amnesic shellfish poisoning.
Scombrotoxic fish poisoning also known as scombroid or histamine fish poisoning, is caused by bacterial spoilage of certain finfish such as tuna, mackerel, bonito, and, rarely, other fish. As bacteria break down fish proteins, byproducts such as histamine and other substances that block histamine breakdown build up in fish. Eating spoiled fish that have high levels of these histamines can cause in human disease. Symptoms begin within 2 minutes to 2 hours after eating the fish. The most common symptoms are rash, diarrhea, flushing, sweating, headache, and vomiting. Burning or swelling of the mouth, abdominal pain, or a metallic taste may also occur. The majority of patients have mild symptoms that resolve within a few hours. Treatment is generally unnecessary, but antihistamines or epinephrine may be needed in certain instances. Symptoms may be more severe in patients taking certain medications that slow the breakdown of histamine by their liver, such as isoniazide and doxycycline.
Ciguatera poisoning or ciguatera is caused by eating contaminated tropical reef fish. Ciguatoxins that cause ciguatera poisoning are actually produced by microscopic sea plants called dinoflagellates. These toxins become progressively concentrated as they move up the food chain from small fish to large fish that eat them, and reach particularly high concentrations in large predatory tropical reef fish. Barracuda are commonly associated with ciguatoxin poisoning, but eating grouper, sea bass, snapper, mullet, and a number of other fish that live in oceans between latitude 35° N and 35° S has caused the disease. These fish are typically caught by sport fishermen on reefs in Hawaii, Guam and other South Pacific islands, the Virgin Islands, and Puerto Rico. Ciguatoxin usually causes symptoms within a few minutes to 30 hours after eating contaminated fish, and occasionally it may take up to 6 hours. Common nonspecific symptoms include nausea, vomiting, diarrhea, cramps, excessive sweating, headache, and muscle aches. The sensation of burning or "pins-and-needles," weakness, itching, and dizziness can occur. Patients may experience reversal of temperature sensation in their mouth (hot surfaces feeling cold and cold, hot), unusual taste sensations, nightmares, or hallucinations. Ciguatera poisoning is rarely fatal. Symptoms usually clear in 1 to 4 weeks.
Paralytic shellfish poisoning is caused by a different dinoflagellate with a different toxin, than that causing ciguatera poisoning. These dinoflagellates have a red-brown color, and can grow to such numbers that they cause red streaks to appear in the ocean called "red tides." This toxin is known to concentrate within certain shellfish that typically live in the colder coastal waters of the Pacific states and New England, though the syndrome has been reported in Central America. Shellfish that have caused this disease include mussels, cockles, clams, scallops, oysters, crabs, and lobsters. Symptoms begin anywhere from 15 minutes to 10 hours after eating the contaminated shellfish, although usually within 2 hours. Symptoms are generally mild, and begin with numbness or tingling of the face, arms, and legs. This is followed by headache, dizziness, nausea, and muscular incoordination. Patients sometimes describe a floating sensation. In cases of severe poisoning, muscle paralysis and respiratory failure occur, and in these cases death may occur in 2 to 25 hours.
Neurotoxic shellfish poisoning is caused by a third type of dinoflagellate with another toxin that occasionally accumulates in oysters, clams, and mussels from the Gulf of Mexico and the Atlantic coast of the southern states. Symptoms begin 1 to 3 hours after eating the contaminated shellfish and include numbness, tingling in the mouth, arms and legs, incoordination, and gastrointestinal upset. As in ciguatera poisoning, some patients report temperature reversal. Death is rare. Recovery normally occurs in 2 to 3 days.
Amnesic shellfish poisoning is a rare syndrome caused by a toxin made by a microscopic, red-brown, salt-water plant, or diatom called Nitzchia pungens. The toxin produced by these diatoms is concentrated in shellfish such as mussels and causes disease when the contaminated shellfish are eaten. Patients first experience gastrointestinal distress within 24 hours after eating the contaminated shellfish. Other reported symptoms have included dizziness, headache, disorientation, and permanent short-term memory loss. In severe poisoning, seizures, focal weakness or paralysis, and death may occur.
