Shellfish poisoning 243

reported among women, while gonorrhea and AIDS were reported more often by men.

Throughout the 1970s and early 1980s, most STD patients could expect to be cured with antibiotics. But about the same time, doctors began to realize that new infections such as the chronic disease herpes and the occasionally fatal illness hepatitis B could not be cured by drugs. With the spread of AIDS in 1982, doctors realized that STDs were again a serious risk to life, and now consider promiscuous sex to be a high-risk venture.

STDs can be diagnosed at special clinics or from specialists in genitourinary medicine and infectious disease. The doctor decides which disease (or diseases) are present and which drugs to prescribe. Once drugs have eased the symptoms, tests are given to make sure the patient is no longer infectious. Treatment is also given to all recent sex partners to prevent transmitting infection. The confidential tracing and treatment of contacts is an essential part of managing STDs.

shellfish poisoning Eating shellfish has been linked to a number of diseases, including those caused by bacteria, a variety of viruses, and toxins.

Shellfish are highly susceptible to bacterial and viral contamination, since they live close to the shore where pollution tends to be worse. While shellfish by themselves are not poisonous, they can become contaminated from their environment, passing infection on up the food chain when eaten by humans. Oysters, clams, and mussels are particularly prone to becoming contaminated because of their metabolic system, which pumps water across their gills to isolate plankton; this makes them vulnerable to bacteria, viruses, and contaminants in the water. (Lobsters and other crustacean shellfish only rarely become contaminated.)

Shellfish contamination caused by bacteria and viruses can be prevented by cooking seafood thoroughly, storing shellfish properly, and protecting them from contamination after cooking. However, traditional methods of cooking seafood (such as steaming clams only until they open) may be insufficient to kill all bacteria and viruses inside them.

Most cases of shellfish poisoning have occurred when people ate raw or undercooked shellfish; in fact, raw shellfish have been linked to nearly 1,000 cases of hepatitis a year. For this reason, doctors recommend that no one eat raw shellfish.

Good data on the occurrence and severity of shellfish poisoning are largely unavailable, which reflects the inability to measure the true incidence of this disease; cases are often misdiagnosed and infrequently reported.

The shellfish industry and government regulatory agencies try to control the problem of shellfish contamination at the source, by seeing that shellfish are harvested from unpolluted beds not tainted by sewage. Unfortunately, these efforts can't guarantee that shellfish from unapproved beds don't reach the market.

Viral contamination The most common viral contamination in shellfish is caused by the Norwalk virus which leads to food poisoning when raw or improperly cooked food has been in contact with water contaminated by human excrement. (See norwalk agent infection.)

It's also possible to contract hepatitis a from eating raw shellfish harvested from sewage-contaminated waters. Even though federal regulations and posting of contaminated waters offer some protection, there is still a risk of contracting viruses when eating raw shellfish.

Symptoms begin from two to six weeks after eating and include fever, weakness, anorexia, jaundice; severe cases may damage liver and can be fatal.

Toxins Shellfish also can become tainted by eating toxic plankton (called dinoflagellates) that multiply rapidly during the warm summer months; because the plankton have a pink or red color, this phe

244 shellfish poisoning, amnesic nomenon has come to be called red tide. Red tides are found in coastal waters in the Pacific from California to Alaska and in the Atlantic from New England to the St. Lawrence. Under good conditions (warm climate, warm water), the plankton may reach 60 million organisms per liter of water. These rapid growths (referred to as a "bloom") discolor the sea and poison fish and marine life. Usually, a person becomes poisoned with the plankton when eating shellfish that have been feeding on them.

The plankton produce a deadly poison called saxitoxin that is so toxic that even one contaminated shellfish can be fatal if eaten. This is why clams, oysters, and mussels are not sold during months without an R in them (the summer months).

Mussels, clams, and oysters are the primary shellfish at risk, and mussels are the most susceptible of all. Healthy bivalve shellfish filter large amounts of toxic plankton, which form the primary ocean food during May through August. During these warm times, the dinoflagellates thrive by photosynthesis and can be so invasive that they kill birds and fish.

The first large epidemic of poisoning caused by red tide-contaminated shellfish occurred in San Francisco in 1927, when 102 people were sickened and 6 died. Today, largely because of the prohibition against eating certain shellfish during the summer months, such epidemics are rare.

Shellfish poisoning caused by toxic forms of dinoflagellates include paralytic shellfish poisoning, neurologic shellfish poisoning, diarrheic shellfish poisoning, and amnesic shellfish poisoning. Each has different etiology, symptoms, and prognosis for recovery, but of the three, paralytic shellfish poisoning is by far the most serious.

Shellfish containing toxin look and taste normal, and usual cooking methods do not affect the toxin. State shellfish screening programs test shellfish for the presence of these toxins and monitor the safety of shellfish harvest beds.

shellfish poisoning, amnesic This type of shellfish poison first came to the attention of public health officials in 1987, when 156 cases of acute intoxication occurred after people ate cultured blue mussels harvested off Prince Edward island in eastern Canada. Of those who got sick, 22 were hospitalized and 3 elderly patients eventually died.

Cause Amnesic shellfish poisoning is the result of an unusual neurotoxic amino acid (domoic acid) that contaminates shellfish. The domoic acid is produced by a phytoplankton called Nitzschia pungens f. multiseries. (Phytoplankton are microscopic, photosynthetic, free-floating organisms in the ocean; N. pungens is a type of phytoplankton with a particular kind of cell wall.) Many different kinds of phytoplankton exist and only a few of them are toxic.

Symptoms While everyone is susceptible to shellfish poisoning, elderly people appear to be predisposed to the severe neurological effects of amnesic shellfish poisoning. Within 24 hours of eating contaminated shellfish, the symptoms begin: vomiting and diarrhea, abdominal pain, and a host of neurological problems, including confusion, memory loss, disorientation, seizure, and coma.

Diagnosis Diagnosis is based on observing symptoms and recent dietary history.

Treatment There is no antidote for this type of shellfish poison. The only treatment is to ease the symptoms.

shellfish poisoning, diarrheic This type of shellfish poisoning is rarely fatal and has not been confirmed in U.S. seafood, although the organisms that produce it are present in U.S. waters. It occurs in Europe in a sporadic, widespread fashion, and an outbreak was recently confirmed in Canada.

Cause It is caused by eating shellfish contaminated by toxin-producing plankton. It is

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