Ciguatera Poisoning

OVERVIEW

• A bizarre poisoning syndrome with acute and sometimes severe neurological and gastrointestinal symptoms caused by eating tropical reef fish that have accumulated ciguatoxin from the dinoflagellate Gambierdiscus toxicus
• most common cause of fish poisoning worldwide.

CAUSE

• ingestion of large predatory reef fish from the tropics e.g. barracuda, grouper, amberjack, and marlin
• Ciguatera-infected fish look, smell, and taste normal (can taste ‘peppery’)
• does not occur in cold water fish

Ciguatoxin

• Ciguatoxin is a lipid-soluble polyether compound
• synthesised by specific bacteria after phagocytosis by the benthic dinoflagellate Gambierdiscus toxicus, which  adheres to dead coral surfaces and bottom-associated algae
• The toxin is then concentrated in the food web as the dinoflagellates are eaten by herbivorous fish species that graze on algae and detritus. These fish are in turn eaten by the larger marine carnivores, which may then be eaten by human
• As the toxin concentration is elevated along the food chain, larger fish are likely to contain larger concentrations of toxin(and an algal bloom need not be occurring concurrent with the presentation)
• toxin concentrates more in fish organs than muscle
• toxin is not affected by not affected by heat or freezing
• ciguatoxins cause increased nerve membrane excitability through their action on voltage-gated sodium channels

CLINICAL FEATURES

• clinical manifestations  vary widely but usually include gastrointestinal, neurologic, and/or cardiovascular symptoms
• symptoms usually start 1–6 hours after the ingestion of fish containing the toxins
• re-exposure to the toxin often leads to worse symptoms

Typical presentation

• GI symptoms initially: diarrhea, nausea, and vomiting
• These symptoms typically last just a few days
• followed by weakness and fatigue, with occasional hypotension or bradycardia
• Features of peripheral neuropathy including dysesthesia, dental pain, and paradoxical disturbance of thermal sensation, are the hallmarks and may last up to 6 months or longer
• Ataxia and seizures have also been described

Hot-cold reversal

• better termed cold allodynia
• considered almost pathognomonic of ciguatera poisoning (other dinoflagellate toxins such as palytoxin may mimic ciguatoxin)
• The phenomenon is probably not a true reversal of temperature sensation, rather pain sensation is altered such that cold is experienced as a burning pain
• The mechanism for this is obscure

DIFFERENTIAL DIAGNOSIS

Sometimes mistaken for

• multiple sclerosis
• chronic fatigue syndrome
• chronic dermatitis

INVESTIGATION

• primarily a clinical diagnosis
• except in severe cases, the results of electrophysiologic studies are usually normal
• detection of ciguatoxin in implicated food sources

MANAGEMENT

Resuscitation

• IV fluids for hypovolaemia
• benzodiazepines for seizures

Specific therapy

• Mannitol (0.5-1g/kg IV, ideally within 72 hours of symptom onset)
  — still recommended by some experts despite a double-blind randomised controlled trial that found no benefit
  — Mannitol’s beneficial effects (if any) may be related to a decrease in neuronal edema, free radical scavenging or sodium/ potassium channel modulation.
  — Mannitol will induce an osmotic diuresis and should only be administered following adequate rehydration of the patient
• Chronic neuropsychiatric symptoms may respond to fluoxetine, and neuropathic pain may respond to amitriptyline and/or gabapentin
  — The evidence base for these treatments is purely anecdotal

Supportive care and monitoring

Disposition

• Patients need to be aware of precipitants that may trigger a relapse — potential triggers include: ethanol, eating fish and other various other foods (including caffeine, nuts, chicken and pork), dehydration and over-exertio
• Potential triggers should be avoided for 6 months following symptom resolution.
• Public health notification to investigate the source and remove the implicated product from distribution

EVIDENCE

Schnorff et al (2002)

• RCT that found no beneift for mannitol
• Criticisms
  — most cases were given mannitol late
  — the subgroup analysis of those receiving mannitol early (within 24 hours) was underpowered
  — case diagnoses were not confirmed by toxin assays of fish samples

References and Links

LITFL

• Seafood poisoning

Journal articles

• Crump JA, McLay CL, Chambers ST. Ciguatera fish poisoning. Postgrad Med J. 1999 Nov;75(889):678-9. PMC1741405.
• Friedman MA, et al (2008). Ciguatera fish poisoning: treatment, prevention and management. Marine Drugs, 6 (3), 456-79 PMID: 19005579
• Perez CM, Vasquez PA, Perret CF. Treatment of ciguatera poisoning with gabapentin. N Engl J Med. 2001 Mar 1;344(9):692-3. PMID: 11229348.
• Scheuer PJ, Takahashi W, Tsutsumi J, Yoshida T. Ciguatoxin: isolation and chemical nature. Science. 1967 Mar 10;155(3767):1267-8. PMID: 6018649.
• Schnorf H, Taurarii M, Cundy T. Ciguatera fish poisoning: a double-blind randomized trial of mannitol therapy. Neurology. 2002 Mar 26;58(6):873-80. PMID: 11914401.
• Winter FD. Ciguatera poisoning: an unwelcome vacation experience. Proc (Bayl Univ Med Cent). 2009 Apr;22(2):142-3. PMC2666861.