Oysters, clams, and mussels are particularly prone to becoming contaminated because of their metabolic systems, which pump water across gills to isolate plankton; this makes them vulnerable to bacteria, viruses, and contaminants. Lobsters and other crustacean shellfish only rarely become contaminated.
Most cases of shellfish poisoning have occurred when people ate raw or undercooked shellfish; raw shellfish have been linked to nearly 1,000 cases of HEPATITIS a year. This is why doctors recommend that no one eat raw shellfish. Another common viral contamination in shellfish is caused by the NORWALK AGENT VIRUS, which leads to food poisoning when raw or improperly cooked food comes in contact with water contaminated by human excrement.
Gonyaulax catanella (popularly known as red tide) is a species of plankton that produces a toxin ingested by shellfish along the North American coasts. Anyone eating shellfish contaminated with red tide can become sick. The type of shellfish poisoning caused by these toxic forms of red tide comes in three forms: neurotoxic shellfish poisoning, erythematous shellfish poisoning, and paralytic shellfish poisoning (PSP). Each has quite different etiology, symptoms and prognosis for recovery, but of the three, PSP is by far the most serious. There is no known antidote for these types of shellfish poisoning; administration of prostigmine may be effective, together with artificial respiration and oxygen as needed.
The shellfish industry and government regulators try to control the problem by seeing that shellfish are harvested from unpolluted beds not tainted by sewage. Unfortunately, these efforts cannot guarantee that shellfish from unapproved beds do not reach the market.