Gambierdiscus toxicus Adachi and Fukuyo, 1979
Ciguatera (pronounced "si gwah teh' rah") is a human illness that results from the consumption of the toxic meat of many species of large, marine, tropical and subtropical food-fish.
Ciguatera toxin(s) are chemical compounds known as polyether substances. Banner, in 1974, recognized that "The disease as presently defined cannot even be attributed to a single toxic compound...." The toxins originate from single-celled, microscopic dinoflagellates, primarily Gambierdiscus toxicus and some other benthic species, which pass through the food web from prey to predator. Ciguatera toxins tend to become concentrated in larger animals near the top of the food chain.
About 400 species of fish and a few invertebrates throughout the marine tropics have been implicated in ciguatera poisonings. Some groupers, snappers, tropical mackerels, barracuda, jacks and hogfish are included among the potential sources of ciguatera. In Florida, large barracuda, grouper and snapper are most often implicated.
One of the first documented sources of ciguatera polyether toxins in the Pacific and Atlantic Oceans was Gambierdiscus toxicus, a single-celled, benthic dinoflagellate about one hundredth of an inch in diameter.
Recently, however, other toxic dinoflagellates, which are usually attached to algae in coral reef environments or shallow waters, have also been implicated. Among the organisms identified as possible toxin-bearing cells are Prorocentrum concavum and P. mexicanum. Several other dinoflagellate species are suspect and are also under investigation. All of them are photosynthetic dinoflagellates. However, more than a thousand other species are not toxin-bearing. Photosynthetic dinoflagellates are important producers of oxygen and organic carbon, hence vital components of the marine environment.
Gambierdiscus toxicus and other ciguateric organisms inhabit tropical and subtropical waters of both the Atlantic and Pacific Oceans. Their distribution is patchy in both space and time. The cells may occur on one side of an island, for example, but not on the other. Their abundance varies with the season, water depth, seafloor (substrate) and environmental factors, such as temperature and salinity.
Preferred habitats of the organisms are areas sheltered from wave action with little freshwater input. The living cells are most frequently found in water down to 100 feet deep. They are usually found attached to larger algae and often associated with coral reefs or other hard surfaces, such as ship wrecks. The organisms seem to flourish following some major disturbance to a reef. For example, ciguatera outbreaks have been associated with construction on or dredging of reefs. Natural disturbances, such as severe storms, may also disrupt reef communities and ciguateric organisms may then increase. In either case, the "clean" exposed hard surfaces are first colonized by macroalgae, which become the substrate for dinoflagellates and other micro-organisms.
As a single-celled organism, Gambierdiscus toxicus reproduces asexually by cell division. However, it probably has a sexual reproductive phase, like many other coastal dinoflagellates.
Dinoflagellates are food for many small marine animals that browse through tropical algal and coral reef communities. In turn, small animals are food to larger crustaceans and fish, and so on through the food web. The larger predators, near the top of this chain, ingest the toxin and are outwardly unharmed. As they continue to feed on ciguateric prey, they continue to accumulate the toxins in their bodies. If these animals are consumed by humans, the toxins in the fish flesh and organs cause the illness known as ciguatera.
Public Health Problems
Each year, ciguatera poisonings in tropical and subtropical regions worldwide are estimated to be in the tens of thousands, with a 1% mortality rate. In endemic areas, such as the Virgin Islands, where people are familiar with the disease, episodes of illness are not always reported to health officials. As a result, case numbers reported by doctors and hospitals are low.
In the United States and its territories, ciguatera is the most frequently reported food-borne disease associated with a naturally occurring chemical (toxin). In the three-years from 1974-1976, 129 cases were documented in a Miami, Florida, study. Ciguatera illness is not considered to be a "reportable" disease, however, nor is the illness always recognized as ciguatera toxicity, so statistics on its occurrence are probably low. In Florida in 1987, two ciguatoxic events were reported to health departments, involving the illnesses of four people who consumed barracuda and grouper. A five-pound barracuda was incriminated in one case.
Ciguatera toxicity is separate and distinct from illnesses in humans due to bacterial contamination from improperly handled seafood.
The ciguatera toxins are temperature-stable, mostly oil-soluble compounds. Cooking, freezing or smoking fish will not destroy the toxins. Unfortunately, the toxins cannot be detected in the meat by appearance or taste.
Symptoms of ciguatera poisoning usually appear in three to five hours after the toxic fish has been eaten. Most victims suffer nausea and vomiting, watery diarrhea, numbness and tingling about the mouth and extremities. More severe cases may suffer muscle pains, dizziness and sensations of temperature reversal, where hot objects seem cold and cold things seem hot. Normal recovery usually requires several days to several weeks.
At this time, treatment is usually symptomatic, easing the distress of nausea, diarrhea and pain. Mortalities are extremely rare.
A 1988 report in the Journal of the American Medical Association documented the use of intravenous mannitol in treating severe cases of ciguatera fish poisoning. "Twenty-four patients with acute ciguatera fish poisoning were treated with intravenous mannitol, and each patient's condition improved dramatically," according to Palafox, et al. Mannitol is apparently the only significant treatment currently available, and under close examination by medical research.
Ciguatera is a national concern since tropical and subtropical seafood is a widely distributed product of commerce. In addition to the public health and product safety problems, ciguatera causes severe economic loss to fisheries and restricts the use of seafood protein in local diets. In the Caribbean, fishermen avoid areas known to produce ciguateric fish and the demand for seafood is met by importation. In the U.S. Virgin Islands, for example, local annual production is about 3.6 million pounds; six million pounds are imported. Puerto Rico produces only 15% of its domestic needs for seafood.
As commercial fishing for tropical reef fishes increases, a rise in the widespread occurrence of ciguatera is expected. In 1980, 12 people in Maryland were afflicted, and in 1982 one case was recorded in Boston. Both incidents involved grouper shipped from Florida. Ciguatera has also been reported in Canada by people who had vacationed in the Caribbean.
A recent consideration has developed in regard to the construction of artificial reefs in areas where the potential introduction of toxic dinoflagellates may initiate ciguatera. Placement of artificial habitats should be carefully considered.
The various symptoms of ciguatera have been documented since the 1500s in the Caribbean and the early 1600s in the Pacific.
The causative organism in the Pacific (G. toxicus) was not identified until the mid-70s. The same organism has since been found in southeast Florida waters and the Caribbean, in habitats similar to those in the Pacific.
Scientists are seeking a simple chemical diagnostic test to detect ciguatoxin in seafood. Current procedures include complicated laboratory techniques and animal assays and are not practical for routine surveillance. In Hawaii, a simple test kit for distribution to fishermen is under consideration.
Included among the goals and objectives of researchers are the following:
Several hundred species of fish and invertebrates have been implicated in ciguatera cases, so continued research efforts are of vital concern.
At the Florida Marine Research Institute, Department of Natural Resources, ciguatera research includes the identification and culture of benthic dinoflagellates of potential toxicity, train- ing other fisheries scientists and researchers in their identification of the organisms, and determining the life cycle and sexual stages of toxic dinoflagellates.
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