Food For Thought
Since moving back to the Bahamas six years ago, I have heard the whispers in closed circles about fish poisoning. Now recently, quite a few friends of mine have contracted the disease. What I don't understand is why so little is done locally to inform the public as to the species to avoid or ways to protect oneself from getting this horrible fate. So, by request of some of my friends who are currently suffering from this, here are some facts about ciguatera.
Ciguatera is a foodborne illness caused by eating certain reef fish whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which live in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are eaten by herbivorous fish whom in turn are eaten by larger carnivorous fish. In this way, the toxins move up the food chain and bioaccumulate. Gambierdiscus toxicus is the primary dinoflagellate responsible for the production of a number of similar toxins that cause ciguatera. These toxins include ciguatoxin, maitotoxin, scaritoxin and palytoxin. Predator species near the top of the food chain in tropical and subtropical waters, such as barracudas, reef snappers, moray eels, parrotfishes, groupers, triggerfishes (turbot) and amberjacks, are most likely to cause ciguatera poisoning, although many other species cause occasional outbreaks of toxicity. Ciguatoxin is odourless, tasteless and very heat-resistant, so ciguatoxin-laden fish cannot be detoxified by conventional cooking.
Hallmark symptoms of ciguatera in humans 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, vertigo, and hallucinations. Severe cases of ciguatera can also result in cold allodynia, which is a burning sensation on contact with cold. Neurological symptoms can persist and ciguatera poisoning is occasionally misdiagnosed as multiple sclerosis.
Dyspareunia (painful sexual intercourse) and other ciguatera symptoms have developed in otherwise healthy males and females following sexual intercourse with partners suffering ciguatera poisoning, signifying that the toxin may be sexually transmitted. Diarrhea and facial rashes have been reported in breastfed infants of poisoned mothers, suggesting that ciguatera toxins migrate into 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 symptoms then reappear. Such relapses can be triggered by consumption of nuts, seeds, 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.
Currently, multiple laboratory methods are available to detect ciguatoxins, including liquid chromatography-mass spectrometry (LCMS), receptor binding assays, and neuroblastoma assays). Although testing is possible, in most cases, LCMS is insufficient to detect clinically relevant concentrations of ciguatoxin in crude extracts of fish.
' Folk' detection
In Northern Australia, where ciguatera is a common problem, two different folk science methods are widely believed to detect whether fish harbor significant ciguatoxin. The first method is that flies will not land on contaminated fish. The second is that cats display symptoms after eating contaminated fish. A third, less common testing method involves putting a silver coin under the scales of the suspect fish. Only if the coin turns black, is it contaminated. It is not known whether any of these tests produce accurate results.
On Grand Cayman Island the locals will test barracuda by placing a piece of the fish on the ground and allowing ants to crawl on it. If the ants continue to move then the fish is safe to eat.
I do not recommend any of these tests as being accurate or safe.
There is no effective treatment or antidote for ciguatera poisoning. The mainstay of treatment is supportive care. There is some evidence that calcium channel blocker type drugs such as Nifedipine and Verapamil are effective in treating some of the symptoms that remain after the initial sickness passes, such as poor circulation and shooting pains through the chest. These symptoms are due to the cramping of arterial walls caused by maitotoxin. Ciguatoxin lowers the threshold for opening voltage-gated sodium channels in synapses of the nervous system. Opening a sodium channel causes depolarization, which could sequentially cause paralysis, heart contraction, and changing the senses of hearing and cold. Nifedipine is a calcium channel blocker. Some medications such as Amitriptyline may reduce some symptoms, such as fatigue and paresthesia, although benefit does not occur in every case. Steroids and vitamin supplements support the body's recovery rather than directly reducing toxin effects.
Mannitol was once used for poisoning after one study reported symptom reversal. Follow-up studies in animals and case reports in humans also found benefit from mannitol. However, a randomized, double-blind clinical trial found no difference between mannitol and normal saline, and based on this result, mannitol is no longer recommended.
Due to the limited habitats of ciguatoxin-producing microorganisms, ciguatera is common in only subtropical and 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. Avoiding consumption of all reef fish (any fish living in warm tropical waters) is the only sure way to avoid exposure. Imported fish served in restaurants may contain the toxin and produce illness that often goes unexplained by physicians unfamiliar with the symptoms of a tropical toxin. Ciguatoxin can also occur in farm-raised salmon. Furthermore, species substitution, labeling a reef fish as a non-reef fish at restaurants and retail, can complicate efforts by consumers to avoid ciguatera.
I have seen the worst this poisoning can give. It's a horrible disease that I wouldn't wish on anyone. It would be beneficial for the Ministry of Health to release information to people on the dangers of this disease. However, we face a double-edged sword. Most of the fish species that carry the toxins are the traditional fish species of the Bahamian diet and are the only source of income for some families as fishing the reef is a way of life here. Since there is no way to know in advance, your best way to stay safe is to avoid reef fish. However, if you don't want to do that, I suggest staying away from boiling or 'stewing' the bones and heads of reef fish as the toxins would be housed in the spinal system and bones as well as the digestive system that usually gets thrown away. I for one will continue to eat Pelagic species instead. Remember, there's more to food than cooking and eating.