Seafood Toxins and Fish & Shellfish Poisoning

Seafood toxins and poisoning are caused by consuming marine fish, bivalve shellfish, and freshwater fish that contain toxins and are responsible for causing foodborne illness worldwide.

Seafood Toxins and Fish & Shellfish Poisonings
Seafood Toxins and Fish & Shellfish Poisonings
  • Fishes contain a full pack of nutrition and are important for a healthy life as it contains omega-3-fatty acid essential for a healthy heart and improves the brain and eye.
  • Although seafood is nutritious, they also serve as a vector for different foodborne illnesses such as amnesic shellfish poisoning, ciguatera fish poisoning, diarrhetic shellfish poisoning, azaspiracid shellfish poisoning, neurotoxic shellfish poisoning, paralytic shellfish poisoning, puffer fish poisoning, Pfiesteria toxin, cyanobacterial intoxication, scombroid (histamine) fish poisoning, other finfish, and shellfish toxins.
  • Seafood poisoning is also associated with bacterial intoxications such as staphylococcal poisoning, Vibrio infections and botulism, and viral infections.
  • During the past five decades, consumption and supply of seafood have increased by a 3.2% rate annually. Therefore, aquaculture is the rapidly growing animal food producing sector.
  • China and other Asia – Pacific regions are mainly affected countries causing gastrointestinal and neurological illnesses.
  • More cases are being reported in nonendemic areas as well due to the increased import of seafood products from endemic areas.
  • Several factors are also involved in incrementing seafood poisonings like adventurous eating habits, climate change, damage to coral reefs, and widespread toxic algal blooms.

Interesting Science Videos

Causes and sources of seafood toxicity

  • Certain dinoflagellate species produce shellfish toxins like bivalve shellfish, mussels, clams, and oysters that accumulate toxins but do not cause harm to themselves as they have a special mechanism that prevents the harmful effects but becomes poisonous to humans.
  • Shellfish and certain finfish species are poisoned by spoilage-causing bacteria or by feeding on toxic algae, which on fish consumption, causes human foodborne illnesses.
  • Blue-green algae and Pfiesteria are known to cause waterborne poisoning of animals and humans sporadically.
  • Marine biotoxins acquire when small fish consumes toxigenic algae that pile up in their skin, viscera, blood, and organs, and then the big fish feeds upon them, and the food chain goes on.
  • Brevetoxins cannot be eliminated or declined by rinsing, cleaning, cooking, and freezing or can be detected by taste or smell, which causes consumers to increase the risk of neurotoxic shellfish poisoning.
  • HABs (Harmful algal bloom) promotes the growth of bacterial poisoning and are outgrowing rapidly over the past five decades, causing harm to animals and the environment.
  • Increase in the import of seafood; the human population is at high risk of seafood poisoning. Therefore, in the United States, Canada, and other countries, improved strategies are taken to assess the risk and characterize the hazards.

Shellfish Toxins

Amnesic shellfish poisoning (Domoic acid)

  • Amnesic shellfish intoxication causes gastroenteritis and affects the nervous system when shellfish contaminated with domoic acid is consumed.
  • Domoic acid is produced by diatoms (Pseudo-nitzschia spp.) and is found in mussels, razor clams, and crustaceans.
  • They are geographically distributed in Northeast Canada, US Northeast and West, Europe, Australia, and New Zealand.
  • Symptoms are usually seen after 24 hours of toxin ingestion, followed by gastrointestinal symptoms like nausea, vomiting, abdominal cramp, and diarrhea).
  • Neurological symptoms are also common, like headaches, seizures, hemiparesis, ophthalmoplegia, and memory loss which may lead to coma.
  • Symptoms of gastroenteritis are resolved within a day or two, but neurologic dysfunction may occur with memory deficits and motor neuropathy.
  • Medical treatment for ASP is supportive care for the patient, and medications are recommended to control seizures and reduce brain lesions.

Ciguatera fish poisoning

  • The ciguatoxin causes ciguatera fish poisoning and maitotoxin produced by dinoflagellate Gambierdiscus toxicus found in large carnivorous tropical and subtropical reef fish like barracuda grouper, moray eel, snapper jack, and seabass.
  • This poisoning is one of the most common seafood-associated illnesses causing approximately 20,000 cases of outbreaks worldwide reported annually.
  • Outbreaks are usually reported in Hawaii, Puerto Rico, the Virgin Islands, the United States, tropical and subtropical waters, the Pacific, Indian oceans, and the Caribbean Sea, where 400 species of fish have been involved ciguatera poisoning.
  • Symptoms involve gastrointestinal, neurological, and cardiovascular, usually occurring 12 – 18 hours after ingestion.
  • Diarrhea, abdominal pain, nausea, and vomiting are the common symptoms of gastrointestinal and begin right after consumption and lasts only a few hours.
  • Neurological signs are dizziness, numbness of lips and tongue, tingling, metallic taste, dryness of mouth, anxiety, blurred vision, temporary blindness, reversal of temperature sensation like hot drink tastes cold and cold ice cream tastes hot.
  • In severe cases, paralysis and death have been reported.
  • The fatality rate is less than 1%, but in a fish outbreak, 0-12% are also reported.
  • Treatment of CFP can be done by supportive attention to respiratory and cardiovascular functions.
  • For acute symptoms, intravenous administration of mannitol and for chronic symptoms, amitryptiline or tocainide have been suggested that help in relief.

Diarrhetic shellfish poisoning

  • Diarrhetic shellfish poisoning occurs from consuming toxic mussels, scallops, and clams and mainly occurs in Japan, northern Europe, South America, South Africa, southeastern Asia, and New Zealand.
  • Sea animals acquiring okadaic acid produced by Dinophysis acuminata cause gastroenteritis following the symptoms of severe diarrhea, nausea, vomiting, abdominal cramps, and fever.
  • The onset period is within 30 mins to a few hours after consumption of toxic shellfish.
  • Treatment is symptomatic, and completely recovers within three days.

Paralytic shellfish poisoning

  • Paralytic shellfish intoxication is a serious life-threatening illness causing unusual neurological disorders resulting in paralysis of the face and limbs.
  • Bivalve mollusks such as clams, mussels, oysters, gastropods, chitons, starfish, and crustaceans accumulate saxitoxin which causes the prevention of sodium ion flow in nerve and muscle cell membranes.
  • Countries with the most reported outbreak are North America, Europe, Japan, South Africa, Indonesia, New Zealand, and South America.
  • Saxitoxin is produced by the unicellular dinoflagellate genus Gonyaulax, which after ingestion, shows symptoms within 30 minutes.
  • This toxin primarily affects the peripheral nervous system and shows initial signs such as a prickly feeling on the lips, tongue, and fingertips.
  • Distal and oral paresthesias with numbness in the extremities and face with a floating sensation causing paralysis of the respiratory system.
  • The intoxication continues causing ascending paralysis from ataxic gait and muscular incoordination.
  • The fatality rate of paralytic shellfish intoxication is 8.5%, where death usually occurs from respiratory failure depending on the concentration of toxin ingested.
  • The lethal dose is considered to be 2-4 mg for humans.
  • If a patient survives the illness, complete recovery is possible and chronic effects of the illness do not occur.
  • Emergency treatment for a patient provides artificial respiration and supportive medical care as there is no effective antidote.
  • More attention should be given to victims with cardiopulmonary resuscitation and respiratory ability, and they should be taken to the hospital as soon as possible.

Neurotoxic shellfish poisoning

  • Neurotoxic shellfish poisoning is a non-paralytic poisoning caused by the brevetoxin produced by the dinoflagellate Ptychodiscus brevis habitat in the red tides.
  • Bivalve mollusks are a vehicle for transmission after consumption. After about 1 to 6 hours, a person starts experiencing parethesias, reversal sensation of hot and cold, bronchoconstriction, rhinorrhea, conjunctivitis,  ataxia, nausea, vomiting, and diarrhea.
  • Neurotoxin shellfish poisoning is rare and is reported to be found in the Gulf of Mexico, Caribbean Sea, Florida, North Carolina, and New Zealand.
  • Treatment is symptomatic and subsides within a few days as symptoms are less severe, and no deaths have been reported.

Pufferfish poisoning

  • Pufferfish poisoning causes perioral paresthesias, nausea, dizziness, weakness, numbness, ascending paralysis, slurred speech, respiratory failure, gastrointestinal pain, and cardiac arrhythmias.
  • Symptoms are caused by the tetrodotoxin, which on ingestion causes poisoning within 6 hours and is believed to be caused by bacterial action of Alteromonas and Vibrio species.
  • Pufferfish, fugu, porcupine fish, and ocean fish are associated with severe neurological illness after ingestion.
  • Other signs of the disease include profuse sweating and salivation, hypothermia, headache, tachycardia, and hypotension.
  • The disease is distributed worldwide but is common in Japan and the Indo-Pacific Ocean.
  • The antidote is not currently available, but treatment can be done by maintaining respiration.
  • In severe cases, the pupillary and corneal reflexes are lost, and acute lung dysfunction is caused.

Scombroid fish poisoning

  • Scombroid fish poisoning is caused by ingesting improperly and inadequately chilled histidine-rich fish like tuna, mahi-mahi, mackerel, and skipjack.
  • Poisoning is caused by a histamine toxin and is commonly reported in Japan, Canada, the United States, England, and most other countries.
  • Symptoms usually occur within 10-90 mins of ingestion which usually resolves within 12 hours.
  • Signs include allergy in the face, neck, upper arms, nausea, vomiting, headache, dizziness, abdominal pain, vomiting, diarrhea, blurred vision, faintness, itching, burning sensation in the mouth, respiratory distress, and shock.
  • The disease is self-limiting, and most cases are mild but hydration and electrolyte replacement help in rapid recovery.
  • Anti-histamine therapy and certain drugs, such as isoniazid or monoamine oxidase inhibitors, are recommended.

Detection methods of Seafood toxins

  • Bioassay using mouse, cat, mongoose, and brine shrimp detect the toxin using enzyme-linked immunosorbent assay and radioimmunoassay.
  • The toxin can be removed within 3 hours of ingestion by gastric lavage with 2 L of 2% sodium bicarbonate by instilling activated charcoal in 70% sorbitol solution.
  • Diagnosis is clinical and can be done by checking the history of eating fish by the patient.
  • Marine biotoxin can be detected by the liquid chromatography-mass spectrometry method.
  • Standard analytic methods include high-performance liquid chromatography, Polymerase chain reaction for detecting histamine and other biogenic amines.

Prevention and Control of Seafood toxins

  • Seafood poisoning originated from the environment especially harmful algal blooms, and its prevention and control can be done during harvest.
  • Sensitive detection methods should do surveillance, sampling, and testing of sea products before exporting.
  • Prompt refrigeration and storing the fish near 0°C decreases the risk of shellfish poisoning.
  • Providing information to improve the safety of handling and processing of seafood must be implemented by regulatory agencies and the seafood industries.
  • Establishing a safety program based on hazard analysis critical control point system is a valid preventive strategy.


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About Author

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Sushmita Dura

Sushmita Dura completed her Master’s degree (M.Sc.) in Food Microbiology from National College, Kathmandu, Nepal. She is interested in Food safety management systems and diseases linked to consuming unhygienic foods.

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