December 2011

Fish and shellfish poisoning

Causes of fish and shellfish poisoning

Ciguatera

Paralytic fish poisoning

Pufferfish poisoning

Scromboid poisoning

What can I do to protect myself?

 

 

 

 

 

 

                                      Photograph courtesy of the NHS Photo Library

Fish and shellfish poisoning, sometimes called marine poisoning, is caused by eating fish or shellfish contaminated with poisons (also known as toxins) made by algae or bacteria. These poisons survive cooking, canning, curing, freezing or smoking. Eating marine poisons can cause mild illness or serious heart, brain or stomach problems and can be fatal, although deaths are rare.

 

Causes of fish and shellfish poisoning

Syndrome	Poison	Seafood	Distribution	Symptoms
Amnesic shellfish poisoning	Domoic acid	Mussels	Eastern Canada	Gastroenteritis, headache,memory loss, seizures
Diarrhetic shellfish poisoning	Okadaic acid	Bivalve shellfish	Japan, Europe, Canada, New Zealand, South America	Gastroenteritis
Ciguatera	Ciguatoxin	Barracuda, snapper, grouper, sea bass, moray eel	Commonest in Caribbean and South Pacific	Gastroenteritis, neurologic symptoms
Neurotoxic shellfish poisoning	Brevetoxins	Bivalve shellfish	Gulf of Mexico, New Zealand	Gastroenteritis, burning/prickling skin, temperature reversal, dizziness, loss of co-ordination
Paralytic shellfish poisoning	Saxitoxin	Bivalve shellfish	Worldwide, commonest in temperate waters	Burning/prickling face and mouth, headache, nausea, vomiting, loss of co-ordination can cause paralysis and be fatal
Pufferfish	Tetrodotoxin	Pufferfish	Worldwide, but commonest in East Asia	Burning/prickling in mouth, breathing problems, dizziness nausea, can cause paralysis and be fatal
Scromboid	Histamine	Mahi-mahi, tuna, mackerel, bonito,  herring,  sardine, anchovy.	Worldwide	Flushing, headache, nausea, vomiting, urticaria

 

Ciguatera

Most ciguatera poisoning occurs after eating fish contaminated with a toxin called ciguatoxin, which grows in coral reefs algae. This is eaten by coral reef fish and becomes concentrated as it moves up the food chain to larger fish which are then eaten by humans. Ciguatera is found in tropical and subtropical waters, including the Pacific and Indian oceans and the Caribbean Sea. Coral reef fish include barracuda, grouper, jacks, moray eels, sea bass and snapper. Ciguatoxin is found in high concentrations in the eggs, guts, head and liver of fish. It resists heat, so cooking does not prevent it.

Symptoms usually appear about four hours after eating contaminated fish, but can be as quick 15 to 30 minutes. Vomiting and diarrhoea are first, followed by a sensation of hot/cold temperature reversal, burning, numbness and then tingling around the mouth, tongue, throat, arms and legs. Painful teeth, abnormal heart rhythms and low blood pressure can occur. Death is rare. With supportive medical care, most people get better in approximately four weeks. However, long term tiredness and distortion of the senses can continue.

Paralytic shellfish poisoning

Paralytic shellfish poisoning (PSP) results from eating clams, cockles, mussels, oysters and scallops contaminated with a strong poison called saxitoxin.

Symptoms generally appear 30 to 60 minutes after eating poisoned shellfish and include:

 

•  Burning, numbness and tingling of the face, lips and tongue.

•  Headache.

•  Nausea, vomiting and diarrhoea.

 

In severe cases, confusion and loss of co-ordination develop, leading to paralysis and breathing difficulties. This may be fatal, but if you survive the first 12 hours of illness, you are likely to live. There is no cure or antidote, although symptoms can be treated.

 

Pufferfish poisoning

Pufferfish poisoning can be fatal and is caused by eating fish containing tetrodotoxin, a potent poison found in ocean sunfish, porcupine fish and pufferfish. These fish are common in the Pacific, Atlantic and Indian Oceans.

In Japan, pufferfish (fugu) is a delicacy eaten in expensive restaurants for potential side effects, which include tingling lips and tongue, a warm sensation and a feeling of joy. Unfortunately, if too much is eaten, these side effects can be severe and lead to nausea and dizziness, general tingling, skin prickling, headache, vomiting and diarrhoea, poor muscle co-ordination and paralysis.

There is no cure and emergency hospital care is often required. In severe cases, breathing problems, a slow pulse and low blood pressure develop. Most deaths, due to breathing difficulties, occur six to 24 hours after the first symptoms start.

Scromboid

Scromboid fish poisoning is caused by eating fish that has not been properly refrigerated. This causes high levels of chemical called histamine (usually only released in response to an allergy) to develop, giving you symptoms similar to an allergic reaction:

• Abdominal cramps.

• Diarrhoea.

• Dizziness.

• Flushed skin.

• Itching.

• Headache.

• Nausea and vomiting.

These symptoms usually appear up to an hour after eating contaminated fish and last for several hours. Treatment is with anti-allergy medicines called anti-histamines, Symptoms usually improve in about four hours.

Fish with naturally high levels of this chemical include: amberjack, anchovy, blue fin tuna, bluefish, bonito, herring, mackerel, mahi-mahi, sardines, skipjack and yellow fin tuna.

 

How can I protect myself?

Reduce your risk by avoiding potentially contaminated fish and shellfish:

 

• NEVER eat pufferfish, moray eels or barracuda.

• Avoid eating reef fish weighing more than three kilograms – this reduces your risk of ciguatera poisoning.

• Do not eat fish heads, guts or eggs.

• Try to make sure all fish is refrigerated properly.

 

Eating shellfish also increases your chance of catching other food and water spread infections, particularly Hepatitis A.

Many developed countries follow strict recommendations for harvesting and preparing fish and shellfish. Warnings are given when fish poisoning is predicted, for instance when large amounts of algae blooms, often called “red tides” appear in the sea. Less developed countries may not always have such guidelines and warning systems.

Links

US Centers for Disease Control: Ciguatera Fish Poisoning.