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 What is Ciguatera Fish Poisoning and where
does it occur?
Ciguatera fish poisoning (CFP)
is a common foodborne disease related to the consumption of subtropical and
tropical marine finfish which have accumulated naturally occurring toxins
through their diet. The concerned –ciguatoxic -fish
are either feeding on small algae species known as dinoflagellates
or feeding on toxic herbivore fish. The main toxic dinoflagellate
is Gambierdicus toxicus
which is found primarily in sub- and tropical areas where it lives in
association with other algae on dead corals.
Are
all tropical area and coral reefs toxic?
No. The majority of coral reefs
are not ciguatoxic. Outbreaks of ciguatera are
limited in distribution and time and are usually very
localised. Thus knowledge of toxic areas is usually
based on local experience from fishermen and consumers. Toxic fish may be found
in the Pacific and Indian Ocean regions and in the
tropical Caribbean. In the Indian Ocean,
endemic areas are known to be around the Reunion island,
parts of Madagascar
and Indonesia.
Ciguatera poisoning is virtually unknown in the Maldives.
Will
the recent Tsunami increase the risk of Ciguatera in the region?
As with any event, either
natural or man-made, that significantly disturbs coral reefs and the
associated eco-systems, there is an increased short- and long-term risk for
ciguatera. This results from the decay
of live corals that provides opportunities for proliferation of seaweeds, on
which benthic toxic microalgae responsible for
ciguatera grow. Therefore, increased
screening for the occurrence of these toxic microalgae
and for contamination of endemic coral fish species for ciguatera toxins in
areas affected by the Tsunami is recommended.
In addition, public education programmes should be carried out.
How to detect ciguatera fish poisoning?
Determinations for ciguatera
are usually limited to symptomatic diagnoses. 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 symptoms are similar to any other food poisoning (abdominal
pain, nausea, vomiting and diarrhea). The most common neurological symptoms
are tingling and numbness in the mouth and the extremities, muscle cramping
and sensation of temperature reversal (a sensory inversion whereby hot or
warm objects feel cold and cold objects may feel warm). Other symptoms
include headache, vertigo, hallucinations, salivation, and perspiration.
Hallucinations seem to be more often reported in cases in the western Indian
Ocean than from other part of the world. The disease is
generally non-fatal and of short duration. However, in a few severe cases,
symptoms can persist for months or even years.
Detection for ciguatera
requires specialized analytical methods and/or particular bioassays. The most
common assay are mouse assays. In recent years, new
rapid tests have been developed and are being evaluated. It is worth nothing
that the toxins isolated in the Pacific, the Caribbean
and in the Indian Ocean all differs slightly and
therefore caution should be taken in using reference material or tests
developed from another region. The pathogenic dose for humans is 23-230 µg
and usual regulatory tolerance is that it must not be detected in a product.
These clinical determinations are limited in practice and depend on a sample
of the actual suspect fish.
What to do in case of a suspected
ciguatera fish poisoning case?
In case of a suspected
ciguatera fish poisoning, consult a medical doctor. Many physicians are not
familiar with ciguatera in particular in areas where this toxin is not
endemic. One should therefore describe the symptoms and concerns.
Unfortunately, there is no single specific remedy for the treatment of
ciguatera fish poisoning. The most successful management of the disease has
been accomplished by supportive and symptomatic treatment such as induced
vomiting. It is important to try to obtain portions of the meal and in
particular the fish to assist in confirming the diagnosis. These portions
should be packaged and frozen for any subsequent analysis.
What can be done to prevent or avoid
ciguatera fish poisoning?
The ciguatoxin
is very heat-stable. Normal household cooking (e.g
boiling, steaming, frying) will not reduce or eliminate the toxin. Consumers
should exercise caution in areas of concern for particular tropical species.
In areas prone to ciguatera Improved hazard analysis for ciguatera
should be established to determine locations, seasonal variation, species
involved, consumers at risk, sources of contaminated fish, etc.
In Cuba, for example, detailed
analysis of epidemiological records on ciguatoxin
poisonings has led to dose/response data being defined as functions of the
size of fish consumed and have allowed limit weights (critical limits) to be
set for five of the most important species and potential toxicity to be set
for another 15 species (regardless of their weight). Similar work could be
done elsewhere to get a better knowledge of size and species of fish to avoid
in a particular area. Targeted information campaigns can then be designed in
the areas and during the periods of the year where the problem is more likely
to occur, to inform target populations of the risk.
Which fish can be ciguatoxic ?
Ciguatoxin
is produced initially by a microscopic alga and is stored in the tissues of
fish species consuming these algae, increasing in concentration in large
carnivorous fishes. Fishes from some reef areas may be toxic, while those
from others may not be. The same species of fish that is ciguatoxic
in one area may be safe in another.
By talking to local fishermen
one can learn which areas to avoid and which fishes may be dangerous to eat.
It is the location where a fish is caught, more than its species,
that determines whether a fish is ciguatoxic.
Therefore, a comprehensive list of non-ciguatoxic
fishes cannot be provided. Between 300 to 400
species of fish have been implicated in ciguatera fish poisoning. If no
information is available, it is wise not to eat any large reef fishes, since
such specimens may have accumulated sufficient toxin during their lifetimes
to be. However, among the large reef fish only very few have been found to be
poisonous
Further reading:
Assessment and Management of Seafood Safety
and Quality, By H.H. Huss, L. Ababouch, L.
Gram, Food and Agriculture
Organization (FAO) of the United Nations, Rome, 2003
http://www.fao.org/documents/show_cdr.asp?
How to perform a
semi-quantitative risk assessment: Ciguatera Fish Poisoning. From : Application of Risk assessment in the Fish
Industry, by J. Sumner, T. Ross and L. Ababouch,
Food and Agriculture Łorganization (FAO) of the United Nation, Rome, 2004. http://www.fao.org/documents/show_cdr.asp?url_file=/docrep/007/y4722e/y4722e07.htm
Ciguatera Fish Poisoning, A Review in a Risk assessment
Framework.,
by L. Lehane, National Office of Animal and Plant
Health, Canberra, 1999. http://www.affa.gov.au/corporate_docs/publications/pdf/animalplanthealth/chief_vet/ciguatera.pdf
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