Neurotoxic shellfish (shell fish) poisoning

Marine algal shellfish poisoning syndromes and ciguatera poisoning/ Marine biotoxins

• most common syndromes are diarrhetic shellfish poisoning, ciguatera poisoning, neurotoxic shellfish poisoning, paralytic shellfish poisoning and amnesic shellfish poisoning

Aetiology:

• multiple naturally occurring biotoxins produced by marine organisms, retained by certain filter feeding bivalves and fish. Some carnivorous gastropods, crustaceans and fish concentrate the toxin in the food chain, leading to toxic effects following ingestion by humans

Epidemiology:

• seasonal variation is observed with more cases occurring during summer months when dinoflagellates growth is greatest
• likely to be an under-reported cause of food-poisoning due to mild cases being un-recognised un-diagnosed by healthcare professionals
• most common syndromes are diarrhoeic shellfish poisoning, ciguatera poisoning, neurotoxic shellfish poisoning, paralytic shellfish poisoning and amnesic shellfish poisoning

Transmission:

• consumption of seafood contaminated by toxin. Person-to- person spread does not occur. Toxins can survive most cooking and freezing processes applied to food

Incubation period:

• few minutes to 24 hours after ingestion

Common clinical features:

• Symptoms vary depending on the specific causative agent and amount ingested
• Ciguatera poisoning:
  • Nausea, vomiting, diarrhoea, cramps, excessive sweating, headache and muscle aches. Neurological symptoms may also occur including altered sensation (burning or pins-and-needles), weakness, itching, dizziness, reversal of temperature sensation, altered taste sensations, nightmares, or hallucinations
  • Onset: minutes to 6 hours after ingestion
  • Duration: 1-4 weeks
  • Rarely fatal
  • due to ciguatera toxins produced by dinoflagellates that accumulate in tropical reef fish (barracuda, grouper, sea bass, snapper, mullet and others). Cases have occurred in UK due to consumption of imported fish
    
    
• Paralytic shellfish poisoning:
  • numbness or tingling of face, arms, and legs, headache, dizziness, nausea and incoordination. Muscle paralysis and respiratory failure can occur in severe cases and may be fatal
  • onset: 15 minutes to 10 hours after ingestion (usually within 2 hours)
  • due to a different red-brown coloured dinoflagellate whose toxin concentrates within certain shellfish (mussels, cockles, clams, scallops, oysters, crabs, and lobsters). Associated with red algal tides. Cases have occurred in UK due to consumption of UK grown and imported shell fish
    
    
• Diarrhoeic Shellfish Poisoning:
  
  • diarrhoea, nausea and abdominal pain. Onset: 30 minutes to 12 hours, duration 3-4 days. Due to dinoflagellate whose toxin accumulates in certain shellfish (mussels, cockles, scallops, oysters and crabs). Associated with red algal tides. Cases have occurred in UK due to consumption of UK grown and imported shellfish
• Neurotoxic shellfish poisoning:
  • numbness, tingling in the mouth, arms and legs, incoordination and gastrointestinal upset. Some patients report temperature reversal
  • onset: 1-3 hours
  • duration: 2-3 days
  • Rarely fatal
  • due to a third type of dinoflagellate toxin found in oysters, clams, and mussels
    
    
• Amnesic shellfish poisoning:
  • diarrhoea and vomiting, and occasionally dizziness, headache, disorientation, and permanent short-term memory loss. In severe poisoning, seizures, focal weakness or paralysis and death may occur
  • onset: within 24hours of consumption
  • may cause long-term problems with short-term memory
  • rare syndrome caused by a toxin made by the diatom Nitzchia pungens and concentrated in mussels and other shellfish

Infectivity:

• person-to-person spread does not occur
• suspected shellfish/fish should be discarded to prevent further cases as cooking, canning, smoking or other processing does not diminish the levels of toxic chemicals

Reference:

1. PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections 2019 Principles and practice. A joint guidance from Public Health England and the Chartered Institute of Environmental Health