Vinod Kumar Verma, Prabjeet Singh,
Dinesh Kumar and Shashank Singh.
College of Fisheries
G.B.P.U.A.T., Pantnagar, Uttrakhand (India)
A biotoxin is any toxin
produced by a living organism (plant,
The toxins produced by various marine organism can be summarized as:-
Dinoflagellates — Pfiesteria, Ciguatera,
Fungi — Stachy botyrs, Fusarium,
Bacteria — Pseudonomas fluorescens
Spirochetes — Borrelai (Lyme disease)
Blue-Green Algae — Microcystis
PARALYTIC SHELLFISH POISONS
Sources and Occurrence
It is caused by a group of toxins (saxitoxins
and derivates) produced by dinoflagellates of the genera Alexandrium,
Dinoflagellates are among the major components of the marine
phytoplankton. They are single-celled organisms, 40 - 50 μm in
PSP toxins occur in, and are produced by, certain unicellular marine
algae known as dinoflagellates, members of the phylum Dinophyta.
Most of the PSP-producing dinoflagellates are found in the genus
chemistry of paralytic shellfish poisons (PSP) has been reviewed by
Shimizu (1978) and Schantz (1980). PSP are a group of toxins
produced by dinoflagellates of the genus Gonyaulax.
The first agent to be chemically characterized was saxitoxin, which,
though it was initially discovered in shellfish in California, has
since been found in greatest concentrations in the Alaskan
from which the name is derived. Saxitoxin has been shown to be a
derivative of tetrahydropurine. It is a white, very hygroscopic
solid, soluble in water, slightly soluble in methanol and ethanol,
but practically insoluble in most non- polar organic solvents. It is
a very basic substance, with two titratable groups, pKa
8.2 and 11.5, and a relative molecular mass of 299.
Symptoms of PSP
The signs and symptoms of PSP in man may range from a slight tingling
and numbness about the lips to complete paralysis and death from
respiratory failure. Typically, the tingling sensation around the
lips, gums, and tongue develops within 5 - 30 min of consumption. In
moderate and severe cases, this is regularly followed by a feeling
of numbness in the finger tips and toes, and, within 4 - 6 h the
same sensation may progress to the arms, legs, and neck, so that
voluntary movements can be made only with great difficulty. In
fatal cases, death is usually caused by respiratory paralysis within
2 - 12 h of consumption of the PSP-containing food.
Sensitivity to PSP is so variable that estimates of the human dose
resulting in death range from 500 μg to 1000 μg to 12 400 μg.
There are no reports of late effects in survivors or of the effects
of long-term, low-level exposure to PSP.
Prevalence in fish and fishery products
Blooms of toxic algae - and outbreaks of PSP -
occur regularly throughout Europe, and the EU-monitoring programmes
regularly detect high toxin levels. The dinoflagellates bloom as a
function of water temperature, light, salinity, presence of nutrients
and other environmental conditions. Blooms of toxic algae have
recently become more prevalent, and many experts believe coastal
pollution and shipping practices have contributed to this expansion.
Water temperature must be (5-8°C for blooms to occur. If temperature
decreases to below +4°C, the dinoflagellates will survive as cysts
buried in the upper layer of the sediments. Shellfish that have fed
on toxic dinoflagellates retain the toxin for varying periods of time
depending on the shellfish. Some clear the toxin very quickly and are
only toxic during the actual bloom. Others retain the toxin for a
long time, even years.
Stability of toxin
The toxic compounds are water-soluble and heat
stable. A 5-minute cook will reduce toxicity by only 30% and
increasing this to 20 min will only effect a 40% denaturation.
Diarrheic shellfish poisoning (DSP)
intoxication characterized by gastrointestinal disturbances, often
occurring as outbreaks associated with the consumption of shellfish,
and consequently named diarrhoeic shellfish poisoning (DSP), has
been reported from several parts of the world, including the Europe,
Japan, South East Asia, North- and South-America. The causative
dinoflagellates, which produce the toxins, are within the genera
These dinoflagellates are widespread, which means that this illness
could also occur in any other parts of the world. A great number of
toxins has been identified including okadaic acid (OA) and associated
toxins (DTX 1-4)
armoured marine dinoflagellate, has been identified as a producer of
DSP in Japan, whereas D.
suspected of being the toxin producer in recent outbreaks in the
Netherlands, based on epidemiological evidence. DSP has not been
detected in cells of D.
attempts to cultivate the organism isolated from Dutch waters have
been unsuccessful. Cases in Chile were associated with the
occurrence of D.
detailed information is not available. Occurrence of one of the DSP
toxins, okadaic acid, has been confirmed in a benthic dinoflagellate,
though involvement of this species in DSP has never been known.
distributed widely but seldom form red tides. It has been noted that
in the presence of D.
a low cell density of 200 cells/litre, mussels and scallops become
toxic enough to affect man. The infestation period in Japan ranges
from April to September.
presence in shellfish of 9 toxic components has been recognized and
the chemical structures of 5 components have been established. These
toxins are classified into two groups: okadaic acid and its
derivatives named dinophysistoxins, and the novel polyether lactones
named pectenotoxins. The chemical structure for dinophysistoxin-2 is
not yet known because of its limited availability, while
pectenotoxin-3, -4 and -5 are closely related to pectenotoxin-1, in
Symptoms of DSP
of signs and symptoms of DSP are diarrhoea (92%), nausea (80%),
vomiting (79%), abdominal pain (53%), and chill (10%). The time from
consumption of shellfish to the onset of illness ranged from 30 min
to several hours, but seldom exceeded 12 h. About 70% of patients
developed symptoms within 4 h. Suffering may last for 3 days but
leaves few after-effects.
Neurotoxic shellfish poisoning (NSP)
disease in human beings associated with red tides involving the
Gymnodinium breve has
been encountered around the coasts of Florida, USA, named neurotoxic
shellfish poisoning (NSP). According to symptoms and mode of
exposure, two syndromes can be identified: (a) NSP associated with
the consumption of shellfish containing cells or metabolites of toxic
symptoms are predominantly neurotoxic in nature and resemble PSP,
except that paralysis does not occur; (b) NSP characterized by
respiratory symptoms and associated with exposure to aerosols of
G. breve cells.
There is however much less data available for this disease, compared
with the other diseases caused by dinoflagellate toxins and
NSP toxic compounds have been isolated exclusively from
G. breve, a
non-thecate (naked) dinoflagellate, encountered around the coasts of
Florida, USA, particularly during red tides, which are initiated in
offshore waters primarily in the late summer and autumn months. The
iron content of the water might be used as a predictive guide, as a
maximum of iron has been observed immediately preceding red tides.
Taxonomically, the organism has recently been transferred to
components share the same skeleton made up of a single carbon chain
locked into a rigid ladder-like novel structure consisting of 11
continous transfused ether rings. The compounds are soluble in
organic solvents but are unstable in chloroform; this has caused
difficulties in isolating the toxins in earlier investigations. The
toxins are not fluorescent and do not have properties that make
detection and quantification easy. Hence, no chemical method for
Symptoms of NSP
In human beings, consuming shellfish
contaminated with G. breve cells,
causes paraesthesia, alternating sensations of hot and cold, nausea,
vomiting, diarrhoea, and ataxia occur within 3 h. Paralysis has not
been observed, and the disease (NSP) appears to be milder than PSP.
An upper respiratory syndrome of NSP has been reported, associated
with aerosols of G. breve cells
and/or toxins, in coastal areas of Florida, USA. The rapidly
reversible syndrome is characterized by conjunctival irritation,
copius rhinorrhoea, and nonproductive cough. There have been no
recorded human deaths from NSP, but the toxin is fatal to fish and
can cause massive fish kill.
Amnesic shellfish poisoning (ASP)
ASP is the only shellfish poison produced by a
diatom. Disease was first identified in Canada in 1987, where more
than 100 people became ill after consuming contaminated shellfish.
Outbreaks have so far been confined to Canada and the USA, although
the responsible algae have been found in many other areas.
Symptoms of ASP
The disease was named after one of the more curious symptoms, which
was loss of short-term memory. Other symptoms include nausea,
vomiting, diarrhoea, headache and neurological effects including
dizziness, disorientation and confusion. In severe cases seizures
followed by coma and death may occur. The short-term memory loss
seems to be permanent in surviving victims.
Ciguatera fish poisoning (CFP)
A variety of fish inhabiting tropical and
subtropical seas may become toxic, and, by ingestion, cause an
intoxication in human beings named "ciguatera", which is
characterized by neurological and gastrointestinal symptoms. The
term ciguatera is of Spanish origin, derived from cigua, which is a
Carribean trivial name for a marine snail, Turbo
pica that, when eaten, is said to
cause indigestion. CFP is one of the most common food-borne illnesses
related to finfish consumption. Its true incidence is not known, but
it has been estimated that 10,000-50,000 people a year suffer from
this disease. It is caused by consumption of fish that have become
toxic by feeding on toxic dinoflagellates or toxic herbivore fish.
been identified as the source of ciguatoxin which is found primarily
in the tropics where it lives in association with macro algae,
usually attached to dead corals. More than 400 species of fish are
known to be vectors of ciguatoxins. Toxins can be detected in the
gut, liver and muscle tissue by means of mouse assay. Some fish may
be able to clear the toxins from their systems. In general,
ciguatoxic species are limited to fish that feed on algae and the
detritus of coral reefs, particularly the surgeon-fish (Ctenochaetus
and the larger reef carnivores that prey on these herbivores. Thus,
the larger carnivores such as moray eels, snappers, groupers,
carrangs, Spanish mackerels, and emperors, certain in-shore tunas,
and barracuda are most toxic.
chemical properties of ciguatoxin have been reviewed by Scheuer
(1982). The chemical structure of ciguatoxin is still largely
unknown. The toxin has been extracted from the the moray eel liver
and, after elaborate purification, has been obtained in a pure
crystalline form as a white solid (Scheuer, 1982). Ciguatoxin is a
highly-oxygenated lipid, soluble in polar organic solvents but
insoluble in water. The relative molecular mass is estimated to be
1111.7 ± 0.3, and possible molecular formulae are C53H77NO24
but other combinations cannot be excluded.
Symptoms of CFP
Clinical symptoms vary widely but are
characterized by gastrointestinal, neurological and cardiovascular
disturbances often within 10 min but also up to 24 h after ingestion
of toxic fish. The initial gastrointestinal symptoms are similar to
any other food poisoning (abdominal pain, nausea, vomiting, and
diarrhea). The neurological symptoms most often encountered are
tingling and numbness in the mouth, hand and feet, muscle cramping
and weakness, temperature reversal, superficial hyperesthasia with a
sensation of burning. Headache, vertigo, stiffness, convulsions,
hallucinations, transient blindness, salivation, perspiration are
symptoms that may occur. A slow, irregular pulse and low arterial
pressure may follow. Cardiovascular disorders usually disappear
within 48-72 h while neurological effects may persist for weeks, even
years in severe cases. Death from CFP is rare (<1% worldwide).
Puffer fish (Tetrodotoxic) poisoning (PFP)
Tetrodotoxin (TTX) is one of the most potent
non-proteinacous toxins known and responsible for numerous fish
poisonings. The toxin is named after the order Tetraodontidae (common
names: puffer fish, balloon fish, globe fish, fugu, toad fish, blow
fish), since many of these fish often carry the toxin. Apart from
Tetraodontidae toxin has been found in goby, blue-ringed octopus,
various gastropods and horseshoe crab. PFP has frequently occurred in
Japan, where these fish are a traditional food item.
Source and Occurrence
is mainly found in the ovaries, liver, and intestines of various
species of pufferfish, lesser amounts being found in the skin; the
body muscle is usually free of the toxin, with the exception of
lunaris lunaris, which
often contains fatal amounts of tetrodotoxin in the muscle tissue
(Tabeta & Kumagai, 1980). The most toxic pufferfish are members
of the family Tetraodontidae,
not all the species in this family contain the toxin. The most toxic
ones are caught along the coasts of China and Japan, and the meat of
these species is considered a delicacy. The amount of toxin in the
roe is related to the reproductive cycle, and is greatest just before
spawning (early summer).
The compound has been obtained from an extract of pufferfish viscera
in the form of colourless crystal prisms that are slightly soluble in
water. It is an aminoperhydroquinazoline compound, with a relative
molecular mass of 319. It has a guanidinium group with a pKa of
11.6, and a unique intramolecular hemilactal bond. The toxin is
unstable at pH levels above 8.5 and below 3.
Symptoms of PFP
Symptoms of PFP occur within minutes and rarely
more than 6 h after ingestion of toxic fish. Nausea and vomiting may
or may not occur, but the most common symptoms are tingling or
pricking sensation and dizziness. Disease may progress to muscle and
respiratory paralysis. Where death occurs it is usually within 6 h
and sometimes as rapidly as 20 min following toxin ingestion. Persons
who have not died within 24 h generally recover completely. The
distribution of the toxin in the fish is mainly in the ovaries
(eggs), liver and skin. The muscle tissue is normally free of toxin.
Control and prevention of natural toxins
The molluscs have to undergo the following
1. Preliminary cleaning in fresh water for a
minimum of two minutes at a temperature of 20°C, plus or minus 2°C.
2. Pre-cooking in fresh water for a minimum of
three minutes at a temperature of 95°C, plus or minus 5°C.
3. The separation of flesh and shells.
4. Second cleaning in running fresh water for a
minimum of 30 seconds at a temperature of 20°C, plus or minus 2°C.
5. Cooking in fresh water for a minimum of nine
minutes at a temperature of 98°C, plus or minus 3°C.
6. Cooling in running cold fresh water for
approximately 90 seconds.
7. The separation of the edible parts (foot)
from the non-edible parts (gills, viscera and mantle) mechanically
with water pressure.
8. Conditioning in containers closed
hermetically in a non-acidified liquid medium.
9. Sterilization in autoclave at a minimum
temperature of 116°C for a time calculated according to the
dimension of the containers used but which cannot be lower than 15 .
This document deals with outbreaks of certain human diseases
associated with human exposure to compounds produced by algae.
Predators feeding on the algae become contaminated by these compounds
which, in this way, enter the human food chain.
Diseases such as paralytic shellfish poisoning (PSP), ciguatera, and
the more recently identified syndromes, neurotoxic shellfish
poisoning (NSP) and diarrhoeic shellfish poisoning (DSP), are
discussed in the document as well as the evidence of their
association with dinoflagellate toxins present in human food.
Tetrodotoxin intoxication (pufferfish poisoning) is discussed because
the compound, which is produced by certain fish in various areas of
the world, has a similar action to that of saxitoxin, one of the main
components causing PSP. Direct dermal contact with toxins causes a
particular type of acute dermatitis, observed in certain areas of the
B.C., Siger, A., & Spiegelstein, M. 1975.Toxins from the blooms
LoCicero, V.R., ed.
Proceedings of the First International Conference on Toxic
Dinoflagellate Blooms, Wakefield,
Massachusetts, Massachusetts Science and Technology Foundation, pp.
J & Gray, J. 1978. Paralytic shellfish poisoning.
Can. Med. Assoc. J.,
R & Fukuyo, Y. 1979. The thecal structure of a marine toxic
Gambierdiscus toxicus gen.
et sp. nov. collected in a ciguatera-endemic area.
Bull. Soc. Jpn. Sci. Fish.,
G.G., Mende, T.J., Lichter, W., & Wellham, l. 1981.
Crystallization and toxicology of T34: A major toxin from Florida's
red tide organism (Ptychodiscus brevis).
C.Y. 1966. Tetrodotoxin, saxitoxin and their significance in the
study of excitation phenomena.
Seafood — Fish — Crustacea
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