Fresh fish poisoning

Ujjwala G Rege, GH Tilve, KG Nair 
 Department of Medicine, Seth G. S. Medical College and K.E.M. Hospital, Parel.. Bombay-400 012, India

Correspondence Address:
Ujjwala G Rege
Department of Medicine, Seth G. S. Medical College and K.E.M. Hospital, Parel.. Bombay-400 012
India

Full Text

The heiroglyphics of the tomb of Ti (2700 B.C.) depict a puffer fish, Tetrao­don Stellatus as a poisonous fish. [4] From that time, marine zootoxins have been recorded, time and again, by man, over the last 5000 years. Since 1970, there has been an increase in the number of poison­ing cases caused by vertebrate fish and shell fish reported to the Centre for Disease Control. [6]

These marine zootoxins are hundreds of times more lethal than snake venoms. They can be subdivided into those that are poisonous to eat, the oral poisons and those that are administered by means of a venom apparatus, the parenteral poi­sons. A third general type of toxin is formed by endogenous glands and re­leased into the surrounding environment by means of pores on the general, body surface, without using a venom purvey­ing structure. [4]

The types of oral fresh fish poisoning, important to be noted in Asia, are as follows:

A. Protozoan Poison

Dinoflagellates, mainly the genera Gonyaulax and Gymnodinium produce this biotoxin. The bivalve mollusks like mussels eat these dinoflagellates. The toxin is concentrated in their salivary glands. When these shell fish are ingest­ed they cause three different types of in­toxication that may or may not be con­current. The first or choleratic type starts within 10/12 hours and consists of transient gastro-intestinal upset. The second or erythematous variety presents with allergic erythema, urticarial rash and severe itching. The third, the para­lytic variety or saxitoxism starts within minutes, with tingling, and numbness. [8] It proceeds to ataxia, and motor para­lysis and may prove fatal within 12 hours. Saxitoxin interferes with the increased sodium permeability required for action potential propagation. The neurotoxin of Gy. breve, when inhaled from the wind blown spray from the red tide, stimulates the postganglionic cholinergic nerve fibres and produces upper respiratory irrita­tion. [3],[4],[6] All these poisons are ,water-soluble, though heat stable, and the con­centration can be reduced to harmless levels by discarding all the bouillon be­fore canning the shell fish.

B. Whelk Poison

Tetramine, a toxin contained in the salivary glands of snails and other bivalves when ingested raw, cooked or canned, produces intense headache, photophobia, impaired visual accommo­dation and paralytic ileus. [4] It has a curare like effect in vitro and is excreted rapidly from the body. The poison can be eliminated by removing the lobulated, yellowish salivary glands.

C. Horseshoe Crab Poison

The unlaid green eggs and even the flesh and viscera of the King Crab and the Asiatic Horseshoe Crab, if eaten dur­ing the reproductive season can result in dizziness, paraesthesiae, diarrhoea, apho­nia, muscular paralysis, loss of consci­ousness and even death . [4] It can be pre­vented by not eating these crabs during the reproductive season.

D. Ciguatoxin

It is an icthyosarcotoxin derived from the flesh and viscera of more than 300 species of vertebrate fishes, highly valued as edible fish. [1] This is not destroyed by cooking, canning or drying. It does not alter the taste of the flesh. [11] It originates from the blue green algae in the food chain of the fish. It produces gastroin­testinal upset followed by tingling, numb­ness, hyperpyrexia, shock, cranial nerve palsies and muscular paralysis with loss of consciousness. A component of cigua­toxin acts as a cholinesterase inhibitor. [7] The prevention of this poisoning is very difficult.

E. Clupeotoxin

This again is an icthyosarcotoxin like ciguatoxin and simulates the latter to a great extent. But the origin of this is in a variety of dinoflagellates. This poison produces sharp metallic taste on inges­tion; and death in 45% of the victims can occur within 15 minutes of inges­tion of the fish.

F. Scombrotoxin

This also is an icthyosarcotoxin consist­ing of histamine, saurine and other heat stable substances, formed by the action of certain marine bacteria, particularly Proteus morganii, on fish flesh. [5] It, on ingestion, produces symptoms suggestive of histamine effect such as itching, urti­caria, bronchospasm and respiratory dis­tress. [2],[3],[9] The spoiled fish flesh looks honeycombed and has a sharp, peppery taste. Hence, it is easy to prevent this poisoning.

G. Tetrodotoxin

This is the most violent form of marine biointoxication, caused by an icthyosar­cotoxin contained in the flesh, viscera and skin of puffers, porcupine fishes and ocean sunfishes, especially when they are eaten prior to or during their repro­ductive period (Near May and June, for tropical seas). This starts within minutes, with paraesthesiae, gastrointestinal upset, and marches rapidly onto extensive para­lysis. The patient remains conscious till the end. The toxin does not alter the taste or smell of fish flesh. It blocks the neuronal action potential. production. Tetrodotoxism accounts for nearly 42% of all poisonings in Japan. [5] Hence the sale of a whole puffer is prohibited in that country. If the fish is skinned, eviscerat­ed and repeatedly washed in alkaline solutions, the toxicity can be reduced to a great extent.

The treatment of all these types of intoxications, so far, is purely symptomatic. It includes parenteral fluids, and when needed, mechanical respiratory aid. No definite methods of management are known still.

The problem of marine biotoxins is as extensive as it is important from the point of view of public health. Innumer­able cases of a wide variety of fish poi­sonings have been recorded from the time of antiquity. In. spite of this, there is total dearth of information on this sub­ject. Very few of the biotoxins have been studied in detail so far. Many of these toxins that have been studied so far, reveal fungicidal, antibacterial, anti­biotic, antitumour, haemolytic, analgesic, cardioinhibitory, psychopharmacological and numerous other types of biological properties. [4] Thus further and deeper study of these toxins will not only hell) to prevent and treat further epidemics of sea fish poisoning but it may reveal an ocean of new and helpful pharmacologi­cal compounds for the service of man­kind.

References