Fish and Shellfish Poisoning
Paralytic shellfish poisoning (PSP) is a nervous system disease caused by eating cooked or raw shellfish that contain environmental toxins. These toxins are produced by a group of algae (dinoflagellates). It is unclear whether these toxins are related to the "blooming" of the algae, also called red tide because the algae can turn the water reddish brown. PSP occurs mostly in May through November.
Causes and symptoms
PSP develops usually within minutes after eating a contaminated shellfish, most commonly a mussel, clam, or oyster. Symptoms include headache, a floating feeling, dizziness, lack of coordination, and tingling of the mouth, arms, or legs. Muscle weakness causing difficulty swallowing or speaking may occur. Abdominal symptoms such as nausea, vomiting, and diarrhea can also occur. Unlike ciguatera and scombroid, PSP may have a much more serious outcome. PSP may cause difficulty breathing related to weakness or paralysis of the breathing muscle. The symptoms may last for six to 12 hours, but a patient may continue to feel weak for a week or more.
PSP diagnosis is based on symptoms after eating shellfish, even if the shellfish are adequately cooked. No blood or urine test is available to diagnose the illness, but tests in mice to detect the toxin from the eaten fish can be done by public health officials.
The treatment of PSP is mostly supportive. If early symptoms are recognized, the doctor will try to flush the toxin from the gastrointestinal tract with medications that create diarrhea. Vomiting may be induced if the patient has no signs of weakness. In cases where the muscles of breathing are weakened, the patient may be placed on a respirator until the weakness goes away. However, this measure is not usually needed. Likewise, the use of a machine to clean the blood (dialysis) has been used in severe cases.
The prognosis for PSP is quite good, especially if the patient has passed the initial 12 hours of illness without needing breathing support. Most deaths occur during this period if breathing help is not available.
Measures to control PSP require detecting rising numbers of algae in coastal waters by periodic microscopic examination. By law, shellfish beds are closed when levels of the toxin-producing organisms are above acceptable standards. Cooking the shellfish does not prevent this disease. Suspected cases should be reported to public health officials.
Barton, Erik D., Paula Tanner, Steven G. Turchen, et al. "Ciguatera Fish Poisoning: A Southern California Epidemic." Western Journal of Medicine 163, no. 1 (July 1995): 31-35.
Eastaugh, Janet, and Suzanne Shepherd. "Infectious and Toxic Syndromes from Fish and Shellfish Consumption." Archives of Internal Medicine 149 (Aug. 1989): 1735-1740.
Gellert, George A., John Ralls, Corwin Brown, et al. "Scombroid Fish Poisoning: Underreporting and Prevention Among Noncommercial Recreational Fishers." Western Journal of Medicine 157, no. 6 (Dec. 1992): 645-647.
Larry Lutwick, MD, FACP
Algae—Plants that have one cell.
Histamine—A chemical found naturally in the body that produces inflammation and increases blood flow; the uncomfortable symptoms of an allergy attack or an allergic reaction are generally caused by the release of histamine.
Toxin—A poisonous substance usually produced by a living thing.