Bacterial Infections: Eating shellfish can be dangerous, and clams are the worst offenders, especially if they are raw. Most problems with shellfish are not caused by true toxins, but by infections caused by ingesting live bacteria. These bacteria grow rapidly at room temperature on moist, cooked foods making them unsafe within a few hours and causing stomach problems such as vomiting, cramps, and diarrhea. Treatment consists of preventing dehydration with a clear liquid diet and possibly antibiotics. One especially severe infection is hepatitis, commonly found in raw clams, oysters, and other shellfish. In addition, some raw fish often contain worms—avoid uncooked seafood unless you know it is safe.
Neurotoxic Shellfish Poisoning (NSP):
Source: Shellfish, especially clams, scallops, mussels, and oysters.
Cause: This illness generally occurs during periods of intense multiplication of dinoflagellates, a phenomenon called "Red Tide," and the subsequent accumulation of these organisms by shellfish. Red Tide usually begins 10 to 40 miles offshore and is usually brought near shore by currents and wind.
Symptoms: Onset of this disease occurs within a few minutes to a few hours afrer ingesting seafood; the duration is fairly short, from a few hours to several days. The symptoms include diarrhea, vomiting, abdominal pain, muscular aches, dizziness, sweating, numbness and tingling of mouth, fingers, and toes.
Treatment: Recovery is complete with few aftereffects—no fatalities have been reported.
Diarrhetic Shellfish Poisoning (DSP):
Source: Shellfish such as scallops, mussels, and clams.
Cause: The toxin produced is okadaic acid, which is again associated with Red Tide blooms.
Symptoms: DSP is generally not life threatening and depending on the dose of toxin ingested, onset of this disease may be as little as 30 minutes and recovery will be achieved in two or three days without medical treatment. Symptoms include nausea, diarrhea, vomiting, abdominal cramps, and chills.
Treatment: Prevent by avoiding shellfish from areas affected by Red Tide. Give lots of fluids and rest.
Source: Tuna, bonito, mackerel, albacore, aku, sardines, anchovies, and numerous other fish part of the Scrombriod order are subject to a special form of poisoning due to spoilage. These fish may taste sharp and pungent.
Cause: Inadequate refrigeration allows marine bacteria to interact with the flesh of the fish and produce histamine and saurine, the chemicals responsible for the symptoms. Scombroid poisoning (also called histamine poisoning) is caused by the ingestion of foods that contain high levels of these histamines, and possibly other amines and compounds. Eating tuna and similar species that aren't freshly caught and/or adequately refrigerated is very risky, especially when you are underway and professional medical attention is not available.
Symptoms: Symptoms include nausea, vomiting, and diarrhea and may require hospitalization, particularly in the case of elderly or impaired patients. Later symptoms may include intense headache, dizziness, abdominal pain, dry burning throat, and pain or difficulty swallowing. This is followed by flushed red skin, itching and hives, and swelling may occur in the face, along with other allergy-type symptoms such as itchy red eyes and nasal congestion.
Treatment: Scombroid poisoning remains one of the most common forms of fish poisoning in the United States. In 1970, some 40 children in a school lunch program became ill from imported canned tuna. In 1973, domestic canned tuna affected more than 200 consumers across the United States and in 1979 and 1980 more than 200 individuals became ill after consuming imported frozen mahimahi (dorado or dolphin fish). Other incidents of intoxication have resulted from the consumption of canned abalone-like products, canned anchovies, fresh and frozen amberjack, bluefish, sole, and scallops.
There may be some benefit from emptying the stomach by inducing vomiting, but this should occur within an hour or so of ingestion to be effective. The symptoms aren't due to allergy to the fish, but they resemble allergy because of the histamine, which is the main chemical intermediary in most allergies. Diagnosis of the illness is usually based on the patient's symptoms, time of onset, and the effect of treatment with antihistamine medication.
You can reduce symptoms by giving antihistamines such as Benadryl, Dramamine, or Phenergan which are widely available in drug stores. These are very well packaged, have a long shelf life, and should be kept aboard for emergencies. Also possibly beneficial would be the H2 blockers such as Tagamet, Zantac, Pepcid, and Axid—over-the-counter versions of some of these are available as well. If there is wheezing or swelling that threatens to close the victim's airway, then an injection of epinephrine (Adrenalin) and steroids such as prednisone should be given.
Source: Over 400 species of fish have been reported toxic with ciguatera at one time or other. The most common are sea bass, grouper, snapper, jack, barracuda, and moray eel. Amberjack, kingfish, dorado (also called dolphin or mahimahi), parrotfish, surgeonfish, triggerfish, filefish, and porgy also carry the toxins, although generally to a lesser degree.
Cause: Ciguatera fish poisoning is caused by a toxin originating in plankton that becomes concentrated as it moves up the food chain of a reef. Whether a fish will be toxic varies mostly with time. Free swimming pelagic fish are usually not a problem, but those that feed on reef fish may be if the plankton is present.
Symptoms: Poisioning symptoms begin between two to 30 hours after eating the fish—the average time is about six hours. Most people begin showing symptoms with vomiting and diarrhea. This stomach distress is followed by the nerve symptoms such as sensory changes, weakness, burning sensations, muscle aches, and these symptoms can be severe.
Treatment: Ciguatera is not usually fatal and the symptoms usually subside over several days. However, you should always seek medical attention if you suspect ciguatera because the poisoning can be severe. Supportive care may be needed and there is progress being made in this area, but there is no treatment—it is a self-limiting disease, but can take months or even years before all symptoms resolve themselves.
There is now a test kit (CiguaCheck) available from Oceanit Test Systems, Inc. (OTS), a subsidiary of Oceanit Laboratories, Inc. Cigua-Check and trade is the first commercial test kit for detection of ciguatera poison in fish and is now available directly from OTS at www.cigua.com.
Amnesic Shellfish Poisoning (ASP):
Source: Clams, mussels, fish, and Dungeness crabs.
Cause: This type of poisoning is a relatively new concern and was first discovered in the Pacific Northwest in November, 1991. Some species of clams may retain the toxin in their flesh and remain poisonous for up to two years after feeding on the affected plankton. The toxin produced here is domoic acid and it can be life threatening. Fish and crab, as well as shellfish, can also contain domoic acid, so the risk to human consumers and animals in the marine food chain is more significant than previously believed. Shellfish beds are closed to harvesting when acid levels reach dangerous levels. It is advisable to avoid eating crab internal organs, which is common in Asian cultures. While the ASP toxin is not as heat stable as the paralytic shellfish poisoning (PSP) mentioned below, it is not completely destroyed by cooking either.
Symptoms: The effects of ASP are characterized by both gastrointestinal and neurological disorders. Symptoms may begin with mild tingling as early as 30 minutes after ingestion, and an upset stomach usually develops within 24 hours after eating the toxic shellfish. Later symptoms include nausea, vomiting, abdominal cramps, and diarrhea. In severe cases, dizziness, headache, seizures, disorientation, short-term memory loss, respiratory difficulty, and coma can occur within 48 hours. Shock from low blood pressure and a slow heart rate are not uncommon, and permanent brain damage or death can occur. The final stages of this toxin are paralysis and death by suffocation. In 1987, four victims died after consuming toxic mussels from Prince Edward Island, Canada.
Treatment: Should you or your crew exhibit any of the symptoms of ASP, vomiting should be induced to expel any remaining shellfish out of the stomach, followed by prompt medical attention. A good cruising boat's first aid kit would be incomplete without some Syrup of Ipecac for this purpose. The victim may need to be put on a respirator if the poisoning turns out to be severe
Paralytic Shellfish Poisoning (PSP):
Source: clams, scallops, mussels, oysters, snails, barnacles, some coral reef snails and crabs, and lobster tomalley (the lobster's liver. It turns green when cooked and is considered a delicacy). Health or fisheries departments often post warnings of shellfish beds that are affected. Not only are cruisers at risk by catching their own dinner, but with the increase in interstate and international transport of seafood, as well as international travel by seafood consumers, there are virtually no human populations that are free of risk.
Cause: PSP is a true toxin concentrated in the flesh of filter feeding marine life, such as clams. It is caused by several species of toxic algae that occur in various coastal waters of the US and the rest of world, especially in the summer months. Cooking does not destroy this toxin and the only way to detect its presence is by lab testing.
Symptoms: Tingling, numbness, ataxia, giddiness, drowsiness, fever, rash, staggering, and possible respiratory arrest.
Treatment: PSP is by far the most serious condition caused by seafood and is life-threatening—treatment should be sought immediately.
Try to identify the source of the poisoning. If there are any nervous system symptoms such as difficulty in speaking or swallowing, visual changes, paralysis, or breathing difficulties, the person should be taken to a hospital as quickly as possible.
If vomiting or diarrhea is severe or prolonged, watch for signs of dehydration. Offer the person fluids, but do not allow him or her to eat. Anti-diarrheal medication may be prescribed by a doctor if diarrhea is persistent, but most often is not indicated if fluid intake is adequate.
Call a doctor or go to a hospital emergency room if the symptoms persist, are severe, or are accompanied by fever, continual localized abdominal pain, blood in the vomit or stool, or abdominal distention.
As with most medical problems, prevention is the key, so know where your seafood was harvested and keep track of local warnings.
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