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Ciguatera Fish Poisoning
By Philip R. Fischer, MD, DTM&H
Dr. Fischer is professor of Pediatrics, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN.
Dr. Fischer reports no financial relationships relevant to this field of study.
Synopsis: Ciguatera fish poisoning is caused by eating reef fish contaminated by algae-produced toxins — even when fish look normal and have been handled and cooked appropriately. Symptoms include neurologic and gastrointestinal abnormalities and can persist for months.
Source: Langley R, Shehee M, MacCormack N, et al. Cluster of ciguatera fish poisoning — North Carolina, 2007. MMWR 2009;58:283-285.
Amberjack fish caught off the Florida Keys, distributed via Atlanta, Georgia, and sold at a fish market in North Carolina were linked to bothersome symptoms in nine individuals. Within a few hours of cooking and eating the fish, the index couple developed diarrhea followed by abnormal temperature and skin sensations. Both improved with the administration of intravenous mannitol.
Seven other people who, at a separate dinner party, ate filets of amberjack fish from the same market also became ill 4-48 hours (median 12 hours) after ingestion of the fish. They reported abnormal skin sensations, joint pains, weakness, shakiness, and/or fatigue. Three had recurrent or worsened symptoms after alcohol consumption. Six of the seven who were sexually active had pain with intercourse (on ejaculation for males, with a burning sensation that lasted up to three hours for females) that recurred for as long as one month. In all nine patients, some symptoms persisted for at least a month; six had resolution of symptoms by six months; and two still had abnormal skin sensations a year after the implicated amberjack meal. Cooked fish was positive for ciguatoxin. One woman was breastfeeding at the onset of symptoms and had no detectable toxin in subsequent breast milk samples.
Ciguatoxins are fat-soluble polyether compounds with potent effects on sodium channels.1 Carnivorous reef fish such as barracuda, amberjack, red snapper, and grouper become contaminated when they eat herbivorous fish that have ingested Gambierdiscus algal dinoflagellates. These algae usually grow in association with coral reefs. The toxin is unrelated to apparent fish health or appearance and, being heat-stable, is not inactivated by cooking.
Ciguatoxins contaminate fish in warm waters, especially in Caribbean and Pacific areas but also in the Indian Ocean. There are multiple specific toxins, but all seem to cause both gastrointestinal and neurologic symptoms. Nonetheless, Caribbean poisoning is predominantly linked to gastrointestinal symptoms while Pacific poisoning is associated with more prominent neurologic findings. Sometimes, the severity of clinical symptoms seems to relate to the amount of toxin ingested, and toxin is most concentrated in fish viscera and gonads. The incidence of ciguatera fish poisoning varies from less than 1 per 10,000 per year in Reunion Island, to 1 per 170 in parts of the Caribbean to 1 per 5,850 in some Pacific islands (such as French Polynesia).2 In fact, 70% of people living on some Pacific islands are thought to become symptomatic sometime during their lives.2 Globally, it is estimated that 50,000 or more individuals likely are affected each year.2
The diagnosis of ciguatera fish poisoning hinges on clinical recognition of key features. Even in endemic areas, however, a third of physicians do not properly diagnose a classic case of ciguatera fish poisoning.2 Vomiting and diarrhea beginning within hours of ingestion of warm water reef fish may be associated with abdominal pain and should raise suspicion of ciguatera fish poisoning; these gastrointestinal effects usually resolve within a few days. Cardiovascular complications such as bradycardia and hypotension occur early in the course of poisoning in only a small number of affected patients and are amenable to fluid resuscitation. Potential neurologic symptoms typically occur earlier in the course of the illness in Pacific Ocean areas, but often follow the initial vomiting and diarrhea in people affected by Caribbean fish. Common neurologic symptoms include parasthesias (with tingling and/or numbness, especially peripherally), itching, myalgia, arthralgia, and fatigue. A specific finding in many people with ciguatera toxicity is that of "temperature reversal" or "cold allodynia" subjects sense burning hot pain when touching cold water or a cold object.3 Neuropsychiatric symptoms seem more common when toxicity occurs in the Indian Ocean but might at least sometimes represent consequences of non-toxin-related concurrent health problems. While painful intercourse previously had been reported, the current series illustrates the possibility of toxins causing frequent, persistent pain with intimate sexual activity.
As experienced by some of the North Carolina patients, subsequent ingestion of alcohol, even after initial symptoms have resolved, can cause repeated ciguatera symptoms. Similarly, recurrences also have been associated with later ingestion of non-contaminated fish, nuts, caffeine, and some meats.2 The reasons for this are not clear, but it has been suggested that some dietary products might trigger changes in fat metabolism and release residual toxin from human fat cells where it is being stored.2 In other subjects, symptoms can persist for months or years without ever fully resolving.
Management requires careful supportive care, and fluid resuscitation may be necessary when gastrointestinal fluid losses are excessive. Mannitol is reported to be helpful, as noted in the index couple in the current report. A wealth of experience points to the value of intravenous mannitol in the treatment of ciguatera fish poisoning, but a randomized, controlled trial found no benefit to this treatment.4 It is not clear, however, whether mannitol was ineffective and should not be used3 or whether the study was flawed in the ways mannitol administration was timed and in the manner by which results were analyzed.2 Many experts still would suggest that mannitol (0.5-1.0 mg per kg body weight, intravenously over 30-45 minutes with repeated doses several hours later if symptoms recur) be used when ciguatera fish poisoning is recognized within three days of ingestion of the contaminated fish. Experiential evidence (without controlled trials) suggests that amitriptyline (and even selective serotonin reuptake inhibitors) can help with persistent pains that follow ciguatera fish poisoning.2
Fortunately, ciguatera fish poisoning rarely is fatal. Similar shellfish-related toxicities, such as neurotoxic shellfish poisoning and paralytic shellfish poisoning, more frequently are fatal. Puffer fish poisoning, common in Japan and often fatal, is caused by a tetrodotoxin that, like ciguatoxin, affects sodium channels.3