Marine toxins (saxitoxin, tetrodotoxin, conotoxin)

Diagnosis of marine toxin exposure is clinical, based on signs and symptoms, and a history of seafood or shellfish consumption, or a history of shell collection, swimming or wading in the sea, diving, or aquarium maintenance.

Confirmation is often made through the identification of the toxin in the flesh of shellfish or fish by the appropriate authorities.

Supportive care is the mainstay of treatment as there are no available effective antidotes for these toxins.

Most patients recover fully with appropriate treatment. Some will have persisting neurological symptoms for days or weeks, but can expect to fully recover after this time.

Marine toxins represent a diverse group of compounds produced by marine flora and fauna that are potentially harmful to humans. Exposure to marine toxins occurs through direct contact with or ingestion of venomous marine creatures or contaminated seafood.

This topic covers the neurotoxins tetrodotoxin, saxitoxin, and conotoxin.

• Saxitoxin is commonly ingested with contaminated shellfish.

• Tetrodotoxin exposure is associated with consumption of puffer fish or direct contact with the blue-ringed octopus.

• Envenomations with conotoxins occur when handling venomous marine snails.

These toxins can cause various gastrointestinal and neurological syndromes by predominantly blocking voltage-gated sodium channels in excitable cells of the heart, muscle, and neuronal tissue. Symptoms after exposure can include perioral paraesthesias, weakness, spreading numbness, and ataxia. While symptomatology depends on the specific venomous species involved, onset is generally rapid and occurs over minutes to hours. Although rare, severe intoxication can cause flaccid muscle paralysis, respiratory failure, and death.[1]Centers for Disease Control and Prevention. Biosafety in microbiological and biomedical laboratories (BMBL) 5th edition. Agent summary statements: toxin agents. Dec 2009 [internet publication]. https://www.cdc.gov/labs/BMBL.html

BMJ talk medicine podcast: marine toxins poisoning, with Dr Jacob Lebin