Ciguatera

Overview
Ciguatera is a foodborne illness poisoning in humans caused by eating marine species whose flesh is contaminated with a toxin known as ciguatoxin, which is present in many microorganisms (particularly the micro-algae Gambierdiscus toxicus) living in tropical waters. Like many naturally and artificially occurring toxins, ciguatoxin bioaccumulates in lower-level organisms, resulting in higher concentration of the toxin at higher levels of the food chain, an example of biomagnification. Predator species near the top of the food chain in tropical waters, such as barracuda, moray eel, parrotfish, grouper, triggerfish, and amberjack, are most likely to cause ciguatera poisoning, although many other species have been found to cause occasional outbreaks of ciguatera. Ciguatoxin is very heat-resistant, so ciguatoxin-laden fish cannot be detoxified by cooking.



History
Originally, ciguatoxin was linked to poison passed to tropical fish through consumption. However, the exact source of the toxin was unknown, and many sources were identified as the culprit. Some of these included the manchineel fruit, cocculus berries, palolo worms, compounds containing copper, pumice, and corallina opuntia.

In Northern Australia, where ciguatera is a common problem, two different methods are widely believed to be available for determining that fish harbors significant levels of ciguatoxin. The first method is that if a piece of fish is contaminated with the toxin, flies will not land on it. The second is that the toxin can be detected by feeding a piece of fish to a cat, as cats are allegedly highly sensitive to ciguatoxin and will display symptoms. It is not known whether there is any veracity to either belief.

Etymological Roots
It is a generally held theory that ciguatera, as a poisonous substance, was named and identified in Cuba, circa the early 1800s. Local folklore has identified that the etymology stems from a story of an Englishman who caught a barracuda on the Isla de Pinos. After consuming the barracuda, the Englishman became terribly ill. When queried about the origins of his illness, the Englishman claimed to have caught and eaten “a fish, from the seawater”. This gave rise to the name of the ailment as ciguatera, a transliteration into Spanish of the English word seawater.

Distribution
Due to the localized nature of the ciguatoxin-producing microorganisms, ciguatera illness is only common in tropical waters, particularly the Pacific and Caribbean, and usually is associated with fish caught in tropical reef waters. Ciguatoxin is found in over 400 species of reef fish, and therefore avoidance of consumption of all reef fish (any fish living in warm tropical waters) is the only sure way to avoid exposure to the toxin. Imported fish served in restaurants have been found to contain the toxin and to produce illness which often goes unexplained by physicians unfamiliar with a tropical toxin and its characteristic symptoms. In addition, ciguatoxin has been found in farm-raised salmon.

In February 2008, the FDA reported that several outbreaks of the disease had been traced to fish harvested near the Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico, near the Texas-Louisiana shoreline. The FDA advised seafood processors that ciguatera poisoning was "reasonably likely" to occur from consuming any of several species of fish caught as far as 50 mi from the sanctuary.

Symptoms
Hallmark symptoms of ciguatera include gastrointestinal and neurological effects. Gastrointestinal symptoms include nausea, vomiting, and diarrhea usually followed by neurological symptoms such as headaches, muscle aches, paresthesia, numbness, ataxia, and hallucinations. Severe cases of ciguatera can also result in cold allodynia, which is a burning sensation on contact with cold (commonly incorrectly referred to as reversal of hot/cold temperature sensation). Doctors are often at a loss to explain these symptoms and ciguatera poisoning is frequently misdiagnosed as Multiple Sclerosis.

Dyspareunia and other ciguatera symptoms have developed in otherwise-healthy males and females following sexual intercourse with partners suffering ciguatera poisoning, signifying that the toxin that produces ciguatera poisoning may be sexually transmitted. As diarrhea and facial rashes have been reported in breastfed infants of mothers with ciguatera poisoning, it is likely that ciguatera toxins are also transferred into the breast milk.

The symptoms can last from weeks to years, and in extreme cases as long as 20 years, often leading to long term disability. Most people do recover slowly over time. Often patients recover but redevelop symptoms in the future. Such relapses can be triggered by consumption of nuts, alcohol, fish or fish-containing products, chicken or eggs, or by exposure to fumes such as those of bleach and other chemicals. Exercise is also a possible trigger.

Treatment
There is no effective treatment or antidote for ciguatera poisoning. The mainstay of treatment is supportive care. Some medications such as the use of Amitriptyline may reduce some symptoms of ciguatera, such as fatigue and paresthesia, although benefit does not occur in every case. Also used are steroids and vitamin supplements, but these merely support the body's recovery rather than directly reducing the toxic effects.

Previously mannitol was used for poisoning after one study reported the reversal of symptoms following its use. Followup studies in animals and case reports in humans also found benefit from mannitol. However, a randomized, controlled, double-blind clinical trial of mannitol for ciguatera poisoning did not find any difference between mannitol and normal saline, and based on this result mannitol is no longer recommended.

There are a number of antiquated Caribbean naturopathic and ritualistic treatments, most of which originated in Cuba and nearby islands. The most common old-time remedy involves bed rest subsequent to a Guanabana juice enema. Other folk treatments range from directly porting and bleeding the gastrointestinal tract to "cleansing" the diseased with a dove during a Santeria ritual. The efficacy of these treatments has never been studied or substantiated; nevertheless they are purportedly still used to this day.