Health & Diving

Hazardous Marine Life

Hazardous Marine Life

Ciguatera

Ciguatera poisoning occurs when contaminated reef fish are consumed. Specific reef fish bioaccumulate toxins produced by microorganisms in their diet. Though ciguatera intoxication should not be fatal, there is no treatment, so it is prudent to become familiar with potentially toxic species to avoid this poisoning.


Source of Intoxication

Ciguatera is caused by ingesting fish contaminated with certain toxins collectively known as ciguatoxins, which are produced by photosynthetic unicellular dinoflagellates (Gambierdiscus toxicus) that are part of phytoplankton. Dinoflagellates are epiphytes, which means they live on macro algae and dead coral surfaces. Small reef fish feed on these corals and macro algae accidentally ingesting these dinoflagellates. As these smaller fish are eaten by larger predators, the toxin is transmitted up the food chain and accumulates in the tissues of top predators through a process known as bioaccumulation. Human poisoning can potentially occur when any of the fish involved in this chain are consumed, but poisoning is much more likely when eating the larger predators.

Species known to be a source of intoxication include barracudas, snappers, moray eels, parrotfish, groupers, triggerfish and amberjacks, but other species have been known to cause occasional outbreaks. Ciguatera toxins rarely contaminate pelagic fish such as tuna, marlins, dolphinfish or other ray-finned fish. Ciguatoxin can be found around the world in the tropical reef belt between 35 degrees north latitude and 35 degrees south latitude.

Epidemiology

Ciguatera is probably the most common type of marine food poisoning. It is endemic in Australia, the Caribbean and the South Pacific islands. Ciguatera cases should be naturally limited to these areas, but due to commercial imports, cases of ciguatera have been reported in areas such as St. Louis, Missouri and New York City.

Approximately 50,000 reported cases of ciguatera poisoning occur annually worldwide. Epidemiological data regarding ciguatera poisoning is challenging to collect; because of the wide array of symptoms, ciguatera is often misdiagnosed or undiagnosed. People in endemic areas often disregard medical evaluation, while imported cases probably go undiagnosed or unreported, because physicians outside of endemic regions may be unfamiliar with symptoms of a tropical toxin. Recent studies have suggested that the incidence of this illness is continuing to increase, though this might be due to increased reporting rather than an increased occurrence of the disease.

Signs and Symptoms

Toxicity depends on exposure and dose (how much is ingested). Symptom onset usually occurs two to six hours after ingestion. Symptoms can last for weeks to years and in some cases may lead to long-term disability.

Signs and symptoms can be highly variable but typically include neurological or gastrointestinal manifestations; about 80 percent of patients show varying degrees of impairment in both systems. The most common manifestations include:
  • Gastrointestinal symptoms such as abdominal pain and gastroenteritis, nausea, vomiting or diarrhea. These initial symptoms typically resolve without intervention within a few hours.

  • Neurological symptoms including paresthesia (tingling and numbness), ataxia (uncoordinated muscle movements) and vertigo

    Persistent feeling of tilting, swaying, whirling or spinning motion of oneself or of the surrounding world when nothing is moving.

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    . Severe cases may include cold allodynia (temperature reversal), a burning sensation upon contact with cold objects. Neurological symptoms may persist and are occasionally misdiagnosed as multiple sclerosis. In patients with a recent history of diving, muscular weakness and pain, these neurological symptoms can also be confused with decompression illness.

  • Skin itching that can persist for weeks and worsen as a result of activities that increase skin temperature such as exercise and alcohol consumption.

Prevention

  • Avoid consuming fish species commonly associated with ciguatera, including barracuda, grouper, snapper, parrotfish, moray eels, triggerfish and amberjacks. Ciguatoxin is odorless, tasteless and heat-resistant — it will not taste different, and cooking will not prevent intoxication.

  • While the whole fish will contain toxins, the highest concentrations are typically found in the liver, intestines and gonads.

Treatment

There is no definitive treatment for ciguatera poisoning. Both first aid and hospital care is aimed at symptom control. If vomiting is profuse, it is important to correct possible dehydration. If you suspect ciguatera, you should seek a medical evaluation. There are many folk remedies, but the efficacy of these has not been studied. The best course of action is prevention through education and avoidance of seafood in endemic or suspected areas.


NOTE: The term ciguatera is actually inaccurate. Don Antonio Parra coined "ciguatera" in Cuba in 1787 to describe an indigestion following ingestion of a type of marine snail called "cigua" (Turbo pica). The term "cigua" was somehow transferred to an intoxication caused by the ingestion of coral reef fish.
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