Toxins originating from marine algae or plankton

Only a few of the large number of marine organisms capable of producing toxins are involved in food poisoning. Poisonings following the ingestion of toxins produced by algae or plankton form significant public health problems in seafood consumption.

Here, two types of marine illnesses will be discussed: shellfish poisoning, a disease resulting from the consumption of shellfish that have ingested toxic algae, and ciguatera poisoning. The latter is caused by ingestion of contaminated fish, in which the toxin has accumulated via a food chain. The alga involved is consumed by a small herbivorous fish. Larger fish feeding on the smaller fish, concentrate the toxin further in the chain. Shellfish poisoning manifests itself in two forms: paralytic shellfish poisoning and diarrheic shellfish poisoning.

Paralytic shellfish poisoning is a neurological syndrome. It is characterized by a sequence of events. Within a few minutes after consumption, signs such as numbness of the lips, tongue, and fingers manifest themselves. After extension of the numbness to the limbs, this is followed by muscular incoordination, paralysis, and death.

Paralytic shellfish poisoning is caused by a mixture of several toxins variously termed paralytic shellfish poison (PSP) and saxitoxin (in fact, a component of the mixture).

PSP is produced by toxic species of the dinoflagellate genus Gonyaulax. Bivalve shellfish (clams and mussels) concentrate the toxin ingested with these organisms. The shellfish are toxic during seasons of algae bloom (so-called "red tide"), i.e., when the concentration of algae is high. Mussels pose the greatest hazard. Paralytic shellfish poisoning is believed to be due to interference of the toxins with ion transport. Saxitoxin is known to block sodium conductance.

Diarrheic shellfish poisoning is characterized by gastrointestinal complaints, including diarrhea, vomiting, nausea, and abdominal spasms. Recently, toxins involved in this poisoning have been chemically identified. They constitute a group of derivatives of a C38 fatty acid, okada acid.

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These diarrheic shellfish poisons (DSP) are produced by the dinoflagellate species Dinophysis and Prorocentrum.

Ciguatera fish poisoning results from the consumption of nondirect plankton feeders. Fish species constituting a food chain concentrate the ciguatera toxins. The fish acquire the toxins by ingestion of the photosynthetic dinoflagellate Gambierdiscus toxicus. This kind of intoxication is found in the South Pacific and the Caribbean.

The various ciguatera toxins do not all contribute to the poisoning to the same extent. The main cause is ciguatoxin. Symptoms of ciguatera poisoning are paresthesia in lips, fingers and toes, vomiting, nausea, abdominal pain, diarrhea, bradycardia, muscular weakness, and joint pain. The mechanism underlying these symptoms may be based on the neuroactivity of ciguatoxin. It increases sodium permeability, leading to depolarization of nerves.

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