Overview – Ciguatera fish poisoning
Ciguatera fish poisoning (CFP) is a rare disorder that occurs because of the ingestion of certain contaminated tropical and subtropical fish. When ingested, the toxin (ciguatoxin), which is present at high levels in these contaminated fish, may affect the digestive, muscular, and/or neurological systems. More than 400 different species of fish have been implicated as a cause of ciguatera fish poisoning, including many that are otherwise considered edible (i.e., sea bass, snapper, and perch). These fish typically inhabit low-lying shore areas or coral reefs in tropical or subtropical areas. In the United States, ciguatera fish poisoning has occurred more frequently in the last decade perhaps as a result of a general increase in fish consumption.
Gambierdiscus toxicus is the dinoflagellate most notably responsible for the production of ciguatoxin precursors, although other species have been identified more recently. These dinoflagellates, which live on the surfaces of seaweeds and denuded corals, are a primary nutritional source for small herbivorous fish. In turn, these small fish become prey for larger carnivorous fish that are subsequently consumed by humans.
Ciguatoxin and other similar toxins are heat stable and lipid-soluble; they are unaffected by temperature, gastric acid, or cooking method. The presence of the toxin does not affect the odor, color, or taste of the fish. In humans who eat contaminated fish, the reported attack rate is 73-100%.
Chemists have successfully synthesized specific ciguatoxins, ensuring that a practical supply will be available for future biological applications. Although not completely reliable, an immunoassay and a mouse biologic assay are available for detection of ciguatoxin in affected fish.
Ciguatoxin produces toxic effects by activation of voltage-dependent sodium channels at the neuromuscular junction. Activation results in membrane hyperexcitability, spontaneous repetitive neurotransmitter release, blockage of synaptic transmission, and depletion of synaptic vesicles. Effects are most pronounced on neuronal, cardiac, and gastrointestinal tissues. Ciguatoxin causes an increase in parasympathetic tone and impairs sympathetic reflexes.
Which fish can be ciguatoxic? (Causes)
Ciguatoxin is produced initially by a microscopic alga and is stored in the tissues of fish species consuming these algae, increasing in concentration in large carnivorous fishes. Fishes from some reef areas may be toxic, while those from others may not be. The same species of fish that is ciguatoxic in one area may be safe in another.
By talking to local fishermen one can learn which areas to avoid and which fishes may be dangerous to eat. It is the location where a fish is caught, more than its species that determine whether a fish is ciguatoxic. Therefore, a comprehensive list of non-ciguatoxic fishes cannot be provided. Over 300 to 400 species of fish have been implicated in ciguatera fish poisoning. If no information is available, it is wise not to eat any large reef fishes, since such specimens may have accumulated sufficient toxin during their lifetimes to be. However, among the large reef fish only very few have been found to be poisonous.
Risk for Travelers
- Over 50,000 cases of ciguatera poisoning occur every year.
- The incidence in travelers to endemic areas has been estimated as high as 3/100.
- Ciguatera is widespread in tropical and subtropical waters, usually between the latitudes of 35 degrees north and 35 degrees south; it is particularly common in the Pacific and Indian Oceans and the Caribbean Sea.
- Fish that are most likely to cause ciguatera poisoning are carnivorous reef fish, including barracuda, grouper, moray eel, amberjack, sea bass, or sturgeon. Omnivorous and herbivorous fish such as parrotfish, surgeonfish, and red snapper can also be a risk.
Ciguatera Fish Poisoning (Toxin) Symptoms
Eating ciguatera toxin contaminated fish result in the following symptoms:
- Symptoms generally begin 6 to 8 hours after eating the contaminated fish but can occur as early as 2 or as late as 24 hours after ingestion.
- Symptoms include nausea, vomiting, diarrhea, muscle pain, numbness, tingling, abdominal pain, dizziness, and vertigo. The classic finding of hot and cold sensation reversal is actually a burning sensation on contact with cold (allodynia).
- Teeth may feel loose and itching may be intense.
- Severe cases of ciguatera poisoning may result in shortness of breath, salivation, tearing, chills, rashes, itching, and paralysis. Bradycardia, coma, and hypotension can occur. Death due to poisoning is rare (less than 0.5 %).
Complications of CFP
Death and serious cardiovascular complications are uncommon.
One bite of fish tainted with ciguatoxins can be enough to cause symptoms. The most common symptoms include stomach cramps, nausea, vomiting, and diarrhea. Other symptoms include itching; numbness of lips, tongue, and throat; blurred vision; low blood pressure; slowed heart rate; alternating hot and cold sensations; and coma. In severe cases, shock, muscular paralysis, and death can occur.
How to Diagnose Ciguatera Poisoning?
Ciguatera is reliably diagnosed by assessing the symptoms and determining if others who consumed the fish suffered from similar symptoms. Since the symptoms usually occur within a few hours of consumption of the fish, it is easy to trace back the source of poisoning.
A new method of diagnosis is the Visual Contrast Sensitivity (VCS). This study is based on the ability of an individual to discern the colors black, grey and white, which is usually impaired in patients affected by a neurotoxin. This test is inexpensive and portable, however, it is not specific only for ciguatera toxin but for all neurotoxins caused by dinoflagellate microorganisms.
Ciguatera poisoning could be misdiagnosed with other forms of neurotoxic poisoning like shellfish poisoning, pufferfish toxicity, botulism, pesticide poisoning, etc. For conclusive diagnosis, the fish can be subjected to laboratory testing to determine if it was infected with ciguatera. Though there are no diagnostic procedures for humans, there exist conclusive lab tests to determine the presence of ciguatera in fish.
How do you treat ciguatera?
Ciguatera food poisoning is treated based on the symptoms expressed by the patient. There is no specific antidote for this food-borne illness that is currently available in the market.
- Earlier, ipecac was used to induce vomiting so that the ingested contaminated food is removed from the system. This is however no longer followed as this method resulted in excessive fluid loss. Instead, activated charcoal is administered within 3 to 4 hours of consumption of the contaminated food so that it prevents absorption of the toxin from the digestive tract.
- Drugs for vomiting are administered to control vomiting and nausea while IV fluids help to replenish the fluid loss. It is important to keep the patient hydrated.
- A good cold shower is recommended for patients with itching along with anti-histamine drugs
- Low blood pressure is managed using IV fluids.
- Vitamin B-12 intake has been found to alleviate a lot of symptoms of Ciguatera toxicity.
- Mannitol is found to be effective when injected into the vein. It appears to act through multiple mechanisms. It should not be used in patients with dehydration unless the dehydration has been corrected.
- Laser and Shenefeld in a case study published in the American Journal of Clinical Hypnosis in 2012 detail the symptoms of a patient with burning feet and hands who did not find relief using other methods but found relief after a single session of clinical hypnosis.
- Inoue M and colleagues published their study in the Toxicon in June 2009 about the use of monoclonal antibodies in the treatment of ciguatera toxicity. This would help in the more effective management of the poisoning.
Prevention of ciguatera fish poisoning
- 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.