| Most
people who have heard of ciguatera associate it with tropical
locations — maybe the South Pacific or Caribbean.
In fact, Bob Shipp’s 1994 edition of Guide to
the Fishes of the Gulf of Mexico states “ciguatera
is strictly a tropical malady, with no verified reports
from the United States mainland areas.”
This
has changed. And recent studies show some occurrences in
Gulf and mid-Atlantic areas.
Ciguatera
poisoning is the most common fish-borne toxin in the United
States, yet mostly unknown in the northern Gulf of Mexico.
Each year some 3,000 cases are reported in the U.S., and
50,000 incidents are reported worldwide. As with many conditions,
the experts think there are a significant number of unreported
cases. The actual number of poisonings could be 10 times
higher.
U.S.
cases come from southern Florida, Hawaii, Puerto Rico, Guam,
Virgin Islands and the Pacific Island territories. The result
is an annual U.S. health cost of around $21 million, which
accounts for almost all the national health costs that stem
from problems with “toxic algae.”
The
ciguatera toxin is produced by a dinoflagellate (Gambierdiscus
toxicus) which grows on reefs and hard structures.
Highest concentrations are found on dead coral.
Bioaccumulation,
or biomagnifications, is the process that leads to the condition.
Small fish accumulate the toxin harmlessly in their tissues
as they graze on the surfaces containing the toxic algae.
Predatory fish then concentrate more of the toxin as they
feed on the grazers.
Hundreds
of different species can have the toxin, but those that
are most likely to end up on a plate are barracuda, snapper,
grouper, shark, mackerels, amberjack and other jacks. All
are piscivorous species that would be expected to consume
smaller reef fishes.
Ciguatera
poisoning can be serious but is rarely fatal. The toxin
affects the digestive, nervous and cardiac systems. Symptoms
can include nausea, vomiting, abdominal pain, diarrhea and
slowed heartbeat. Patients also report intense itching,
joint pain and tingling sensations. The reversal of cold-hot
sensations, where cold is felt as burning hot, is also common.
Symptoms
can first appear in an hour or two, and for some patients,
tingling sensations have lasted as long as 25 years. People
who have been exposed to the toxin become sensitized –
each subsequent exposure results in amplified symptoms.
Researchers have found that the South Pacific form of ciguatoxin
is particularly potent – as much as 10 times more
active than the Caribbean form.
In the
last 10 years, several isolated cases of ciguatera poisoning
have occurred in the U.S. outside of expected areas. In
1998, two people who ate snapper and barracuda caught at
a rig off Texas experienced probable ciguatera poisoning
(no fish was left for testing). In 2004, two people who
ate barracuda caught off the coast of South Carolina definitely
experienced ciguatera poisoning (remaining fillets tested
positive). And this last March, a Galveston couple grew
ill after eating portions of a 34-lb gag grouper caught
at the Flower Garden Banks off the Texas-Louisiana border.
It had
been generally assumed that concentrations of ciguatoxin
below 0.5 parts per billion don’t cause illness. Some
experts say that 1 ppb is the illness threshold for Caribbean
ciguatoxin. However, the grouper that sickened the Texas
couple had a ciguatoxin concentration of 0.6 parts per billion,
and the poisoned man said that the effects were the worst
thing that had ever happened to him. His wife was hospitalized
for 13 days.
Treatment
for ciguatera poisoning has traditionally been to address
the individual symptoms, but recent publications indicate
that intravenous mannitol may be fairly effective overall.
There is a treatment hotline – 305/361-4619 or 305/661-0774.
No one
really knows whether the fish that caused these three cases
picked up the toxin locally or migrated in from areas with
chronic infestations. A study conducted in 2003 found some
Gambierdiscus toxicus on each of six oil rigs tested
off the Texas coast.
Tests
of 20 barracuda taken near Texas showed traces of ciguatoxin
in half the fish, though none were classified as toxic.
This study also reported some Gulf tagging and tracking
data for several fish species. Barracuda proved to be long-distance
travelers. Three of the barracuda migrated more than 600
miles across the Gulf; one barracuda was caught near Sanabel
Island, Fla., in 1992 and then near the south Texas coast
in 1994. Some king mackerel and amberjack also moved long
distances.
Should
Louisianans change their fishing or dining habits because
of ciguatera? Definitely – if they are in Guam.
When
considering fish from the northern Gulf of Mexico, we have
to remember that there are millions of fish eaten every
week that are perfectly fine. The risk of ciguatera poisoning
from these fish is extremely low.
If anything,
the few people who eat barracuda from the northern Gulf
(and barracuda is surprisingly good) may want to know that
there is a slight risk. Stay tuned: Researchers have proposed
that the problem may get worse with global climate change,
widespread coral die-offs or with more artificial reefs.
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