Ciguatera is a food-borne illness brought on by eating fish contaminated with ciguatoxins, a potent neurotoxin, produced by dinoflagellates such as Gambierdiscus toxicus. They adhere to algae, coral, and seaweed where herbivorous fish eat them. Larger carnivorous fish will suffer a toxin build-up from consuming these herbivores. Ciguatera is endemic to tropical and subtropical specifically South Pacific and Caribbean. However, it is found worldwide anywhere fish are consumed. It affects other parts of the world where it is not indigenous through importation of contaminated fish. The fish that most commonly cause Ciguatera are barracuda, grouper, moray eel, amberjack, sea bass, sturgeon, parrot fish, surgeonfish, and red snapper.
Gambierdiscus toxicus is the dinoflagellate responsible for the production of some similar toxins that cause ciguatera. These include ciguatoxin, maitotoxin, palytoxin, scaritoxin, and palytoxin. Predator species in tropical waters are most likely to cause ciguatera poisoning. Barracudas, groupers, moray eels, snapper, and amberjacks are commonly implicated, but it is also found in over 400 species of reef fish. Ciguatoxin is tasteless, odorless, lipid soluble, and heat-resistant, so ciguatoxin-laden fish cannot be detoxified by normal cooking.
Ciguatera is the most common worldwide fish poisoning with up to 50,000 cases occur globally every year. This number is felt to be underreported because most physicians do not realize that it is a reportable disease. While thought to be endemic to the South Pacific and Caribbean, it was recently isolated in the Red Sea and the Atlantic Ocean. It affects 3% of travelers to the endemic regions. It is the most common fish-related foodborne illness in the United States. Ciguatera is most commonly caused by eating barracuda, grouper, moray eel, amberjack, sea bass, sturgeon, parrot fish, surgeonfish, and red snapper.
Ciguatoxin decreases the threshold for opening voltage-gated sodium channels in synapses of the nervous system. Opening a sodium channel causes depolarization, which may cause paralysis, heart contraction, and change the senses of hot and cold. Cold allodynia is a unique symptom of ciguatera. Cooking or freezing the fish does not prevent Ciguatera as these methods do not kill the ciguatoxin. It has no odor. Researchers are looking at the possibility of maitotoxins playing a larger role in Ciguatera fish poisoning. When introduced to mice by intraperitoneal injection and oral consumption it caused toxicity. Further research is being done on Ciguatoxins by introducing the toxin to human brain-derived cell lines to evaluate its toxicity.
Ciguatoxin can also be found in blood, liver, muscle and brain tissue.
Signs and symptoms of ciguatera toxin in humans include gastrointestinal and neurological effects including nausea, vomiting, diarrhea, headaches, muscle aches, paresthesia, numbness, vertigo, ataxia, pruritus without urticarial and hallucinations. Neurologic symptoms include a wide range of symptoms such as peri-oral numbness and tingling, a metallic taste in the mouth, blurred vision. Severe ciguatera toxicity can result in cold allodynia, which is a burning sensation on contact with cold (patients will note cold being perceived as hot). Persistent ciguatera toxicity may be misdiagnosed as multiple sclerosis. Dyspareunia has developed following sexual intercourse suggesting the toxin may be sexually transmitted. Mothers who breastfeed have reported diarrhea, as well as, facial rashes in their infants. This supports the theory that ciguatera toxins are transmitted into breast milk. Cardiovascular signs can include bradycardia and hypotension. Cardiac symptoms are only present in the early stages of the toxicity. Alcohol consumption during toxin ingestion has been found to increase the risk of developing bradycardia, hypotension and altered skin sensation. Signs and symptoms can last from weeks to years although most recover with occasional relapse. Relapse may be triggered by consumption of alcohol, nuts, seeds, fish, chicken, and eggs. Symptoms can last days, weeks, or months.
Multiple tests are available to detect ciguatoxins including liquid chromatography-mass spectrometry (LCMS), neuroblastoma, and receptor binding assays. These tests are not readily available at the time of patient presentation in the emergency room. Routine laboratory testing is often non-specific and rarely helpful. Treatment is based on history and physical, as well as disease progression.
The treatment of ciguatera poisoning is supportive care. There is no specific antidote for the toxin. If the patient’s nausea and vomiting are not severe, activated charcoal may be used in the first few hours of toxicity to prevent further absorption of the ciguatoxin. Antihistamines can be used for pruritus. Symptomatic relief of nausea and vomiting should also be provided. Dehydration can occur due to nausea and vomiting. The isotonic saline infusion should manage this. If intravenous (IV) fluid resuscitation is not sufficient, then IV pressor infusion may be added. There is evidence that calcium channel blockers such as nifedipine and verapamil are useful in treating some symptoms. In rare cases, patients may experience respiratory failure and should be managed by traditional rapid sequence intubation. Symptomatic bradycardia is treated with intravenous atropine. Medications such as amitriptyline may reduce some symptoms, such as paresthesia and fatigue. Steroids and vitamin supplements support recovery but do not reduce toxic effects. Mannitol was once used for ciguatera poisoning, but a clinical trial found no difference between mannitol and normal saline.
Diagnosis is often difficult, as physicians do not recognize symptoms and hesitation to report. Ciguatera has similar symptoms to scombroid and other enteroviruses. Ciguatera can be mistaken for organophosphate toxicity, botulism, multiple sclerosis, Guillain-Barre syndrome and a wide range of other food poisonings.
The toxicity of ciguatera is generally self-limiting with symptoms generally only lasting few days.
There are multiple unproven lay methods to detect ciguatera toxicity. Some believe flies do not land on contaminated fish; cats become ill after eating contaminated fish; putting a silver coin under the scales of the suspect fish, if the coin turns black, it is contaminated; and placing a piece of the fish on the ground and allowing ants to crawl on it, if the ants survive, the fish is safe to eat.