Ciguatera Poisoning

Reef Fish

Reef Fish

Dr. Reed presented a case that she encountered while in her Rural Medicine Rotation in Hawai'i of an 80 y/o female who initially presented to the ED with acute onset nausea, vomiting, and diarrhea, after eating locally caught reef fish. The fish was caught by her son the day prior. They all had a family dinner that night where she ate poke, beef, and cooked fish (including the liver). Patient’s daughter is present and states that she ate most of the same food (except the liver), but had no symptoms. Review of systems was notable for burning pain when touching cold items (cold allodynia), which is a common symptom in Ciguatera poisoning.


  • Most common nonbacterial food poisoning associated with fish in the United States
  • Most U.S. cases occur in Florida and Hawaii
    • With transportation of imported fish nationwide, all clinicians need to be aware of ciguatera
  • Involves tropical and semitropical marine coral reef fish common in the Indian Ocean, the South Pacific, and the Caribbean Sea
  • ~ 80 cases per year in Hawaii
  • Global estimates predict that 20,000–50,000 people may be affected by this poisoning each year.
  • Most cases in Hawaii come from recreational catches rather than fish bought in markets (don’t worry tourists!). (3)


  • Ciguatera-toxin producing algae may be ↑ due to warmer sea temperatures
  • Toxin CTX-1 activates astrocytes and astroglia
  • Ciguatoxins interfere w/ neuronal Na+ channels -> Na+ channels open @ resting membrane potential
  • Uncontrolled sodium influx -> uncontrolled membrane depolarization & repetitive action potentials
  • Entry of Na+ into neurons -> water into cytoplasm  axonal edema
  • Ciguatoxins may also inhibit neuronal K+ channels
Courtesy JAMA 2013

Courtesy JAMA 2013

Clinical Presentation

  • The onset of symptoms:
    • Within 15–30 min of ingestion
    • Typically within 2–6 hours
  • Symptoms ↑in severity over the ensuing 4–6 h
  • Most victims develop symptoms within 12 h of ingestion, and virtually all are afflicted within 24 h
  • Diarrhea, vomiting, and abdominal pain usually develop 3–6 h
    • May persist for 48 h and then generally resolve (even without treatment)
  • Common symptom: dysaesthesia/cold allodynia
    • Reversal of hot and cold tactile perception (burning pain on exposure to cold), which develops in some persons after 3–5 days
  • Most resolve spontaneously within weeks, but some continue to have symptoms for months or even years after onset
  • More severe reactions tend to occur in persons previously stricken with the disease.
  • Persons who have ingested parrotfish (scaritoxin) may develop classic ciguatera poisoning as well as a “second-phase” syndrome (after 5–10 days’ delay) of disequilibrium with locomotor ataxia, dysmetria, and resting or kinetic tremor. This syndrome may persist for 2–6 weeks.


  • Made clinically
  • No routinely used laboratory test detects ciguatoxin in human blood
  • Liquid chromatography–mass spectrometry is available for ciguatoxins but is of limited clinical value because most health care institutions do not have the equipment needed to perform the test
  • Ciguatoxin enzyme immunoassay or radioimmunoassay may be used to test small portions of the suspected fish, but even these tests may not detect the very small amount of toxin (0.1 ppb) necessary to render fish flesh toxic. A newer neuroblastoma assay may be sufficiently sensitive to detect small amounts of toxin but is not readily available for clinical use. (1,2)


  • Supportive
  • Ondansetron for nausea
  • Hydroxyzine and cool showers for pruritus
  • Syrup of ipecac and activated charcoal are not recommended for ciguatera poisoning
  • Hypotension may require the administration of IV crystalloid and, in rare cases, pressors
  • Amitriptyline (25 mg PO twice a day) reportedly alleviates pruritus and dysesthesias. In three cases unresponsive to amitriptyline, tocainide has appeared to be efficacious
  • IV infusion of mannitol may be beneficial in moderate or severe cases in fluid-repleted patients, particularly for the relief of distressing neurologic or cardiovascular symptoms, although the efficacy of this therapy has been challenged and has not been definitively proved.
    • The infusion is rendered initially as 1 g/kg per day over 45–60 min during the acute phase (days 1–5). If symptoms improve, a second dose may be given within 3–4 h and a third dose may be administered the next day.
    • The mechanism of the benefit against ciguatera intoxication is thought to be due to hyperosmotic water-drawing action, which reverses ciguatoxin-induced Schwann cell edema. Mannitol may also act in some fashion as a “hydroxyl scavenger” or may competitively inhibit ciguatoxin at the cell membrane. (5)


  • No way to identify ciguatoxic fish by look, color, smell, taste or texture
  • Toxins not destroyed or inactivated by cooking, canning, drying, freezing, or smoking
  • Don’t eat reef fish or fish that feed on reef fish
  • If you eat it, don’t eat the internal organs, head, or eggs
    • Ciguatoxin can be 100x more concentrated in these parts of the fish
  • Severity of illness is directly related to amount of toxin eaten

Thanks again to Dr. Reed for another fascinating case!


  1. Olson KR. Poisoning. In: Papadakis MA, McPhee SJ, Rabow MW. eds. Current Medical Diagnosis & Treatment 2018 New York, NY: McGraw-Hill.
  2. Thomas, C and Scott, S. All Stings Considered: First Aid and Medical Treatment of Hawaii’s Marine Injuries. University of Hawaii.
  3. Lei C, Badowski NJ, Auerbach PS, Norris RL. Disorders Caused by Venomous Snakebites and Marine Animal Exposures. In: Kasper D, Fauci A, Hauser S, Longo D, Jameson J, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 19e New York, NY: McGraw-Hill; 2014.
  4. JAMA patient page. Ciguatera fish poisoning. JAMA. 2013 Jun 26;309(24):2608
  5. Michael E. Mullins & Robert S. Hoffman (2017) Is mannitol the treatment of choice for patients with ciguatera fish poisoning?, Clinical Toxicology, 55:9, 947-955, DOI: 10.1080/15563650.2017.1327664