Fish poisoning

Organism Fish poisoning is a specific form of food poisoning caused by toxins present in the fish or shellfish when they are caught or which develop due to partial decomposition taking place if they are not eaten straight away or refrigerated. Ciguatera toxin is produced by the dinoflagellate Gam-bierdiscus toxicus, which is present in algal blooms, often called red tides, while shellfish poisoning can de due to the dino-flagellates Gonyaulux, Gymnodinium, Dinophysis or Alexandrium.

Clinical features Symptoms are normally mild with paraesthesia (tingling and burning sensations or pain and weakness), malaise, sweating, diarrhoea and vomiting, but in the young or those who have consumed a large quantity of poison, the condition is more serious. Respiratory and motor paralysis can occur, often resulting in fatalities. Neurological symptoms can persist for some time after the original illness.

Transmission is through eating fish that has not been refrigerated or already contains the toxin. At certain times of the year and when hurricanes, seismic shocks or similar disturbances of the coral reef occur, an algal growth containing the dinoflagellate develops. Fish feed on the algal bloom, or it is inadvertently filtered by shellfish, and their flesh becomes poisoned. Fish that are normally quite edible, such as barracuda, snappers, sea bass and groupers, become poisonous at these periods. The commonest poison is ciguatoxin, which is not destroyed by cooking.

Incubation period 0.5-3 h after eating fish or shellfish.

Period of communicability Not transmitted from person-to-person.

Occurrence and distribution Fish poisoning is commonly found amongst island communities or coastal people in which fish is a major item of diet. It is an important problem in Pacific Islands, the Caribbean, Southeast Asia and Australia.

Control and prevention All freshly caught fish should be gutted and refrigerated as soon as caught, unless cooked and eaten straight away. Red tides (algal blooms) occur as a result of some disturbance of coral reefs, such as hurricanes, earthquakes and El Nino climatic disturbances. Algal blooms and hence fish poisoning are related to the surface temperature. As a result, where this is abnormally increased during an El Nino event, there is an increase in fish poisoning and the converse when the temperature is less than expected.

Treatment There is no specific treatment; supportive therapy being given.

Surveillance When red tides are reported, eating reef fish should be avoided.

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