Editor's note: This is the second of a three-part series
Infectious, toxic syndromes from fish and shellfish consumption
There are several major categories of problems that can occur from eating seafood. We'll try to organize them into the agents involved: viruses, bacteria, parasites and toxins.
Eating raw shellfish, such as oysters and clams, increases the chances of contracting the Hepatitis A and Norwalk viruses.
Clams and oysters are filter feeders, which means they concentrate bacteria that come from shore.
Fecal-oral spread is basically what happens here. Septic tanks in an area upstream from the oyster beds can cause this.
Hepatitis A causes flu-like symptoms, low-grade fever, nausea, vomiting and sometimes yellow skin. Boiling the fish for four to six minutes usually is adequate to prevent this.
The Norwalk virus has an incubation period of 24 to 48 hours during which period you may not be sick. Nausea, vomiting, diarrhea and abdominal cramps last one to two days and it usually resolves. Steaming shellfish for at least four to six minutes is generally enough to prevent this infection.
Vibrio is a large group of bacteria that cause cholera and other illnesses. Typically, these produce a profuse watery diarrhea and vomiting, usually no fever is present and it may last up to a week.
Supportive care and tetracycline antibiotics help speed resolution.
Some of these bacteria can even enter through broken skin and cause problems.
Other causes of "food poisoning" that can happen via land-based foods can also happen with seafood. Appropriate care of your food is always a good rule to follow. If it's been heated, serve it hot. Don't let it sit around at room temperature. Once the meal is over, seal things up and chill them on ice or in the 'fridge or freezer.
Giardia or fish tape worms and roundworms are the culprits here.
Cooking usually removes any risk, but for the sushi afficionados out there, make sure you know the source of your seafood.
Ciguatera is a poison that accumulates in fish, especially in "predator fish" such as the larger reef fish that we like to eat. A fat-soluble toxin is progressively concentrated from smaller fish through larger fish - large snapper, grouper, barracuda, sea bass, tuna, kingfish and others - until the final apex predator (us) eats the fish. The larger the fish, the more likely the toxin will be present.
The toxin is not broken down by heat or freezing, is odorless, tasteless and hard to avoid, though it is somewhat rare. It's found in tropical waters during the spring and summer months. Incubation period ranges from two to 24 hours. Not only does it cause GI symptoms, such as nausea/vomiting/diarrhea/cramps, it also causes interesting neurologic symptoms, altered sensations and burning feet and hands. The classic sign is heat/cold sensory reversal; hot things feel cold and vice-versa.
Symptoms may last one to two weeks, worsen with alcohol use, but can last for years. Treatment requires medical attention and avoiding alcohol.
This is commonly mistaken as an allergy to fish and happens often with tuna, mackerel, kingfish, dolphin and bluefish. The darker-fleshed fish have histamine-like substances that cause flushing and heat sensations, burning in the throat and palpitations. The toxin is not inactivated by heat. Proper refrigeration at all stages after the fish is caught is essential to prevent this from happening.
Paralytic shellfish poisoning
Caused by eating mussels, clams, oysters and scallops that have concentrated the dinoflagellate responsible for causing "red tide" summer blooms.
Symptoms include abnormal sensations of the mouth and extremities, a sensation of floating, followed by progressive loss of coordination then weakness and paralysis.
GI symptoms are less common. Survival beyond 12 to18 hours gives a good prognosis. The toxins are water-soluble and heat won't inactivate them. Supportive hospital care may include ventilator support.
Neurotoxic shellfish poisoning
This occurs from a different dinoflagellate, similar to red tide along the Florida coast, that contaminates filter-feeding mussels. The heat-cold reversal may be present, clumsiness happens, but it's usually not as severe a disorder as the paralytic shellfish poisoning. Vomiting and diarrhea can also occur.
Rare in the U.S., this intoxication is more common in Japan from eating sushi prepared from the puffer fish. Heat won't inactivate this toxin found in the skin and guts of the fish. Within three hours the floating sensation, seen above with PSS, can occur along with sensory changes, clumsiness and weakness. Only severe cases lead to paralysis. Severe vomiting can also occur. Treatment is best done in the hospital, as the condition can progress and become lethal.
R.J. Oenbrink of Tequesta Family Practice is a board certified doctor of osteopathy. His offices are located at 395 Tequesta Drive, Suite B. Send your questions to: firstname.lastname@example.org. He is available to speak to groups on this or a variety of other topics. Please call his office, if interested, at (561) 746-4333.