For further information....
THE
CIGUATERA
(An
overview by A.Carbonnière)
1) What
is ciguatera?
Ciguatera
has been taking its toll for a long time. Its
occurrence was reported back in 1606 on Vanuatu. The description given
in 1774 by Captain Cook of the symptoms from which members of his crew
were suffering in New Caledonia corresponds to the disease as it is
known today.
Ciguatera
is caused by toxic substances accumulating in the muscles and viscera
of herbivorous fish and their predators. These natural substances
originate from a benthic micro-organism, the dinoflagellate Gambierdiscus
toxicus (other dinoflagellates may also be involved,
such as Prorocentrum lima, P. concavum, P. hoffmannianum, P.
cassubicum, P. mexicanum, P.miniumum, Ostreopsis lenticularis, O.
siamensis, O. ovata, O. mascarensis, O. heptagona, Amphidinium carteri,
A. klebsii and Coolia montis)
The micro-organism responsible for ciguatera (or
"gratte") in Polynesia is a unicellular algal organism which
clings to the macroalgal substrates colonising dead coral complexes.
It is capable of synthesizing at least two families of toxins,
including the ciguatoxins, which subsequently undergo a process
of bioaccumulation
in the fish (herbivorous grazers and carnivorous predators) which ingest
them. Humans, who constitute the final link in this toxic food web,
can also be intoxicated by eating carnivorous fish such as barracuda,
sting fish, stone bass, sturgeon and seriola.
Table
of toxins produced by the various dinoflagellate species
|
Species
|
Toxins
produced
|
Toxic
effects
|
|
G.toxicus
|
maitotoxin,
ciguatoxin
|
neurotoxic
|
|
C.monotis
|
no
name
|
hemolytic
|
|
O.lenticularis
|
ostreotoxin
|
neurotoxic
|
|
O.heptagona
|
unknown
|
-
|
|
O.ovata
|
unknown
|
hemolytic
|
|
O.siamensis
|
unknown
|
hemolytic
|
|
O.mascarenensis
|
maitotoxin
|
neurotoxic
|
|
P.concavum
|
okadaic acid
|
diarrhetic
|
|
P.lima
|
okadaic acid
|
diarrhetic
|
|
P.mexicanum
|
fast-acting
|
hemolytic
|
|
P.hoffmanium
|
okadaic acid
|
diarrhetic
|
2) Causes
of Ciguatera
Gambierdiscus
is endemic to Polynesia, although the
populations are not very dense. Occasionally, as the result of
environmental factors which have not yet been clearly identified, a
massive proliferation or bloom of these algae occurs in their natural
habitat. One of the environmental factors on which the frequency of
these blooms probably depends is the temperature. In Tahiti, cyclic
blooms of G. toxicus occur according to a seasonal pattern: the
highest densities tend to be recorded during the hottest part of the
year (from September to March).
Another
factor contributing to the propagation of this disease is the decline
of the madreporarians, which has cleared newly available surfaces for
colonisation by the macro-algae which provide G. toxicus with
an ecological niche. The spatio-temporal pattern of distribution of G.
toxicus therefore depends on the decline of the madreporarians.
Consequently, the destruction of coral due to the occurrence of
cyclones, coral bleaching and anthropic activities,
as well as to marine pollution is generally followed within a variable period of time by
blooms of ciguatera, which result in an increase in the number of
humans intoxicated.
|
The
presence of toxins in the fish is episodic and unpredictable,
and often occurs shortly after storms. |
3)
The effects of ciguatoxin:
Intoxication
by ciguateric fish can cause gastro-intestinal and neurological
symptoms and shock, and can in some rare cases even be lethal. The
most frequent symptoms are diarrhea, vomiting, abdominal cramps, sweating, shivering, painful muscles and
joints, paralysis, false heat perception, tingling sensations or
numbness of the mouth, faintness and visual disturbances or
temporary blindness. In the most severe cases, cardio-vascular
difficulties or respiratory insufficiency can occur. The
neurological symptoms can last for several weeks or even months.
4)
The geographical regions involved
Cases
of intoxication by Ciguatera affecting both residents and
tourists have been recently reported in the following places: the
Virgin Islands of the United States, the British Virgin Islands,
Puerto Rico, the Bahamas, Haiti, The Dominican Republic, Jamaica
and all the subtropical and tropical islands of the West Indies
and the Pacific and Indian oceans where the species of fish
mentioned above are eaten.
5)
A warning to gourmets !!
The
large fish usually served in restaurants store higher levels of
ciguatoxin than the smaller fish. Consumers have no means of
telling whether or not the fish they are about to eat have been
contaminated, since they look, smell and taste just like healthy
fish. It is sometimes possible to detect a slightly metallic taste.
Since the toxin is not destroyed by heat, cooking the fish does
not eliminate the risk of toxicity; on the contrary, the
concentrations increase due to the evaporation of the water
present in the flesh. The only really safe preventive measure
available is to refrain from eating fish.
|
The
intoxication of human beings and the damage to
aquaculture, fishing and the tourist industry are liable
to have serious economic and social repercussions in the
regions involved. |
For
further information, you can consult the extremely instructive
Institut Malardé site:
http://www.malarde.pf/cigua_1f.htm
http://ourworld.compuserve.com/homepages/honu/malarde/francais/ciguatex.htm
and
others :http://www.ifremer.fr/francais/produits/thau/page7.htm
http://vm.cfsan.fda.gov/~mow/chap36.html
http://www.fishbase.org/manual/FishbaseThe_CIGUATERA_Table.htm
|
Atoll_site_