Pathophysiology

During conditions of inadequate preservation or refrigeration, the musculature of dark-fleshed or red-muscled fish undergoes bacterial decomposition.^33,361 The normal surface bacteria Proteus morganii, Klebsiella pneumoniae, Aerobacter aerogenes, Escherichia coli, Alcaligenes metalcaligenes, and others have been implicated in the putrefactive process, which includes decarboxylation of the amino acid L-histidine to histamine and saurine (a phosphate salt of histamine).⁴⁶² This most often occurs when fish is held at ambient or high temperatures for several hours.¹¹³ The term saurine originated because of the association of scombrotoxism with saury, a Japanese dried fish delicacy.²¹⁴ Because of this process, “scombrotoxin” was initially thought to be histamine, which is commonly found in large amounts in the flesh of the fish usually implicated. Evidence initially suggesting that histamine may be the causative toxin of scombroid fish poisoning was presented in an investigation of a small outbreak.³²⁷ The urinary excretion of histamine and its metabolite, N-methylhistamine, was measured in three persons in this series who had scombrotoxism after ingestion of marlin. There was no increase in the principal metabolite of prostaglandin D₂ (a mast cell secretory product considered to indicate release of histamine from mast cells), supporting the hypothesis that the excess histamine was from the fish rather than endogenously produced in the victims. Histamine levels greater than 20 to 50 mg/100 g are frequently noted in scombrotoxic fish, and it is not unusual to record levels in excess of 400 mg/100 g.⁴¹⁷ However, it is possible that some other compound may be responsible for scombroid symptoms, because the syndrome cannot be reproduced solely by administration of equal or even massive doses of histamine by the oral route. Histamine is rapidly inactivated by enzymes in the gastrointestinal tract and on first pass through the liver, with very little reaching systemic circulation. Other compounds, such as cadaverine or putrescine, may be present in the decomposed fish flesh and may either facilitate the absorption or inhibit the gastrointestinal or hepatic degradation of histamine.^396,462 Whatever the causative toxin, it is heat stable and not destroyed by cooking. Affected fish typically have a sharply metallic or peppery taste but may be normal in appearance and color. Not all persons who eat a scombrotoxin- or histamine-contaminated fish become ill, possibly because of uneven distribution of decay within the fish.

Clinical Presentation

The effects of scombroid fish poisoning occur within minutes after consumption of the fish. The symptoms are similar to an allergic reaction (which it is not) and typically include headache, diffuse erythema, sense of warmth without elevation in core temperature, nausea, vomiting, diarrhea, abdominal cramps, conjunctival injection, pruritus, dizziness, and burning sensation in the mouth and oropharynx.^30,246,313 Flushing of the head, neck, and upper torso is characteristic. Severe effects, such as bronchospasm, generalized urticaria, hypotension, palpitations, and dysrhythmias, have been reported but are not frequent.^174,214 In most healthy victims, the syndrome is self-limited, resolving within 6 to 12 hours. In rare cases, symptoms can persist beyond 24 hours.²¹⁶ In patients with preexisting respiratory or cardiac disease, the effects of the poisoning can precipitate more severe illness.^49,313 Scombroid reactions may be markedly more severe in patients taking isoniazid (INH) because of this compound’s blockade of gastrointestinal tract histaminase.⁴⁸⁵ Death has never been reported after scombroid poisoning. Assays of histamine and its metabolite in urine samples of scombroid-poisoned patients demonstrated elevated levels compared to controls, although histamine measurement is neither common clinical practice nor recommended. Histamine levels poorly correlate with clinical manifestations and do not affect management decisions.

Treatment

Gastric decontamination for scombroid poisoning is not indicated because symptoms occur rapidly and vomiting can be a primary effect of the toxin. Symptoms can be lessened or controlled with administration of histamine-1 (H₁) receptor antagonists, such as diphenhydramine or hydroxyzine, administered initially in doses of 25 to 50 mg orally or intravenously. Histamine-2 (H₂) receptor antagonists (e.g., cimetidine, famotidine) have also been shown to relieve most of the symptoms; perhaps a combination of H₁ and H₂ receptor antagonists would be most effective.^44,188 Vomiting is usually controlled by an antihistamine, but occasionally requires addition of a specific antiemetic, such as ondansetron. The persistent headache of scombroid poisoning may respond to cimetidine or a similar drug if standard analgesics are not effective.¹⁸ Intravenous fluids and inhaled bronchodilators should be used as needed. Vasopressors are rarely necessary because hypotension is usually mild and responds to intravenous fluid administration. Corticosteroids are generally not indicated, because this illness is a toxic reaction and not immune mediated.

Prevention

The only effective method for prevention of scombroid fish poisoning is consistent temperature control at <−40° F (≤4.4° C) at all times between catching and consumption.¹¹³ It has been difficult to reduce the occurrence of scombroid poisoning in the United States; recreational catches likely plays a major role.²¹⁶ No fish should be consumed if it has been handled improperly or has the smell of ammonia. Fresh fish generally has a sheen or oily rainbow appearance; “dull” packaged fish should be avoided. If an episode of scombroid poisoning is recognized, it is important to report it promptly to local public health authorities to prevent additional exposures, particularly if the food was served in a public eating establishment.²¹⁵

Pathophysiology

Tetrodotoxin blocks the action potentials in nerves by binding to the pores of the voltage-gated, fast sodium channels in nerve cell membranes. TTX has a unique nonprotein structure and is widely used as a research tool to study sodium channels. Mouse bioassays demonstrate that the minimal lethal dose of TTX by intraperitoneal injection is 8 to 20 mg/kg.³²⁸ The interaction of TTX with the sodium channel is thought to be stoichiometric, with each TTX molecule interfering with one channel. TTX affects the spike-generating process of sodium channels, not the resting or steady-state voltage.²⁴²

TTX interferes with both central and peripheral neuromuscular transmission. Although it is not a depolarizing agent, in animals it causes depression of the medullary respiratory mechanism, intracardiac conduction, and myocardial and skeletal muscle contractility. At the microcellular level, the mechanism of action of TTX is linked to the axon rather than to the nerve endplate. TTX blocks axonal transmission by interfering with sodium conductance within the depolarized regions of the cell membrane, perhaps by acting at a metal cation binding site in the sodium channel, without affecting presynaptic release of acetylcholine or its effects on the neuromuscular junction.^4,207 There is no apparent effect on potassium permeability.³⁹³ Saxitoxin, implicated in paralytic shellfish poisoning, has essentially the same action as does TTX on the nerve membrane, although it is believed to have a discrete receptor.²⁴⁶ The poison in freshwater puffers may be composed of TTX or saxitoxin, the predominant toxin depending on the species. The LD₅₀ (dose at which 50% die) for mice is 10 mg/kg when TTX is administered by intraperitoneal, intravenous, or subcutaneous routes.⁴⁷³

Animal studies suggest that TTX has a peripheral effect that results in vasodilation independent of α- or β-adrenergic receptors.^226,245,292 Further studies suggest a dose-dependent action. At low doses, systemic blood pressure is lowered, although perfusion pressure is initially maintained. Higher doses of TTX result in a profound fall in blood pressure.²⁴² Experiments with animal models using TTX from blue-ringed octopi demonstrate similar profound hypotension. Agonists (norepinephrine or phenylephrine) have been the most effective agents in raising blood pressure in models of TTX poisoning.¹⁵⁰

Clinical Presentation

Clinical manifestations typically develop within 30 minutes of ingestion but may be delayed by up to 4 hours. During a 2002 outbreak in Bangladesh of 37 people (from eight families) who were poisoned from inadequately prepared puffer fish, 31 of the victims developed symptoms within two hours and eight died.² Death has been recorded within 17 minutes of exposure. The extent and type of symptoms vary according to the individual and amount of TTX ingested. Usually, paresthesias of the lips and tongue are followed by several signs as mild as diaphoresis, to life-threatening, such as hypotension, respiratory failure, and coma.⁸⁴ Other commonly described symptoms include weakness, headache, body paresthesias, and gastrointestinal symptoms such as nausea, vomiting, and abdominal pain. Hypersalivation, ataxia, cyanosis, dysphagia, aphonia, dyspnea, blurred vision, bronchorrhea, and bronchospasm have also been described.^2,84,93 Early miosis may progress to mydriasis with poor pupillary light reflex.⁴⁷³ A disseminated intravascular coagulation-like syndrome is heralded by petechial skin hemorrhages that can progress to bullous desquamation and diffuse stigmata of prolonged coagulation. Hypotension can be profound and may be refractory to treatment. Bradycardia and atrioventricular node conduction abnormalities may be present. Complete cardiovascular collapse with respiratory paralysis precedes death. Normal consciousness may be maintained until shortly before death.^156,473 In some older reports, 60% of victims died, most within the first 6 hours. Survival past 24 hours is a good prognostic sign.

Treatment

Treatment of TTX is primarily supportive with aggressive airway management and assisted ventilation.⁴²⁹ Decontamination should be considered with 1 g/kg of activated charcoal given as soon as practical following presentation. Atropine may be used to treat bradycardia in conjunction with adequate oxygenation (SaO₂ > 92%). Intravenous fluid resuscitation should be initiated for hypotension; however, use of vasopressors may be required to maintain perfusion. α-Agonists such as phenylephrine or norepinephrine are more likely to be effective. No antidote is currently available to treat TTX poisoning; however, studies are ongoing.

Cholinesterase inhibitors, such as edrophonium and neostigmine, have been used to treat victims of TTX poisoning with mixed results. Some case reports have suggested subjective improvement in neurologic symptoms after administration of cholinesterase inhibitors.^90,473 A recent case series suggested that neostigmine may help overcome respiratory muscle paralysis, which is the predominant cause of death.⁹⁰ Other case reports noted no improvement after infusion of these compounds.^2,301,470 Antihistamines and steroids have also been utilized without clear benefit.³⁰¹

A minor intoxication with TTX may be limited to paresthesias and mild dysphagia. In such a case, the victim should be observed in the emergency department or intensive care unit for at least 8 hours to detect deterioration, particularly in respiratory function. The victim should not be discharged until the symptoms are clearly improving. Although water soluble, TTX is very difficult to remove from fish, even by cooking. It is prudent to avoid all puffers, even when prepared by an expert.

Pathophysiology

The blue-green and free algal dinoflagellate Gambierdiscus toxicus is thought to be responsible for producing ciguatoxins.⁴⁴³ G. toxicus adheres to dead coral surfaces and marine algae that are consumed by smaller herbivorous fish.^176,269 Although G. toxicus is very likely responsible for the majority of ciguatoxins encountered in fish, the cyanobacterium Trichodesmium erythraeum can produce water- and lipid-soluble precursors to the toxins that may generate ciguatera syndrome.¹³⁷ Other dinoflagellates, such as Prorocentrum concavum, Prorocentrum mexicanum, Prorocentrum rhathymum, Gymnodinium sanguineum, and Gonyaulax polyedra, may generate toxins that play a role in ciguatera syndrome.^373,471

Larger reef fish eat the contaminated smaller fish, thereby becoming vectors as ciguatoxin is bioconcentrated up the food chain. As fish within the food chain become larger and older, the toxin is accumulated.^{102,204,214,361} Although the entire fish is toxic, the viscera (particularly the liver) and roe are considered to carry the highest concentrations of toxin.²⁸ No plankton feeders have so far been reported to be ciguatoxic.

It has been suggested that proliferation of toxic algae may be triggered by contamination of water from a number of sources, including industrial wastes, golf course runoff, metallic compounds, ship wreckage, or other pollutants.¹⁹⁴ In the Marshall Islands (Micronesia), consequent to nuclear testing, the incidence of toxin-producing plankton has tripled.³⁸² Similar observations have been made with respect to various military activities (dumping and explosives) in the Line Islands and Gilbert Islands (Kiribati, Central Pacific), Hao Atoll (Tuamotu Archipelago, French Polynesia), Gambier Islands (French Polynesia), and others.³⁹² Yet another cause of toxic dinoflagellate proliferation may be transfer and dumping of ballast water from large oceangoing vessels.

Ciguatera is associated with more than five toxins, including fat-soluble quaternary ammonium compounds (ciguatoxins), a water-soluble component (maitotoxin, from the Tahitian vernacular name maito for the striated surgeonfish Ctenochaetus striatus), a maitotoxin-associated hemolysin (lysophosphatidylcholine, or lysolecithin), and a ciguatoxin-associated adenine triphosphatase (ATPase) inhibitor.^{197,281,287,402} Scaritoxin (isolated from Scarus gibbus) is similar to the fat-soluble component and is specific to parrotfishes.⁸⁶ Lipid-extracted toxins from G. toxicus have been designated GT-1, GT-2, and GT-3; a water-soluble toxin is designated GT-4.^122,318 Chemical analysis of ciguatoxins demonstrates that they closely resemble brevetoxin C (from P. brevis) and okadaic acid, isolated from marine sponges and the dinoflagellate Prorocentrum lima.^148,331 Identification of okadaic acid from the Caribbean dinoflagellate P. concavum lends support to the notion that this toxin may be more significant in ciguatera poisoning than previously thought. Another compound, named prorocentrolide, has also been found in reef-dwelling fish with okadaic acid and has been implicated in diarrhetic shellfish poisoning, another common fish-borne illness.^148,213

Three major ciguatoxins (CTX-1, CTX-2, and CTX-3) are usually found in the flesh and viscera of ciguateric fishes. Each is found in variable concentrations, which may account for inconsistency of reported clinical signs and symptoms.²⁸⁷ CTX-2 is a diastereomer of CTX-3.²⁸⁶ Ciguatoxins may result from oxidation of gambiertoxins, possibly through the cytochrome system in the liver of fish.²⁸⁸ The lipid components have been characterized as crystalline, colorless, heat-stable compounds of approximate 1100 daltons molecular weight, with functional hydroxyl and quaternary nitrogen groups.

Ciguatoxins are potent Na⁺ channel toxins and exert their effects by activating voltage-sensitive Na⁺ channels. The Na channels open at resting membrane potentials, leading to spontaneous firing of neurons, giving rise to the neurologic signs and symptoms of ciguatera.²¹⁹ One mechanism of their action may be that they falsely occupy calcium receptor sites that modulate sodium pore permeability in neural, muscle, and myocardial membranes.³⁵ This effect could allow increased membrane permeability to sodium and cause sustained depolarization. Electrophysiologic studies of the sural and common peroneal nerves in humans with ciguatera, demonstrating reduced light touch, pain, and vibratory sensation in the extremities, showed prolongation of the absolute refractory, relative refractory, and supernormal periods. These findings indirectly suggest that CTX may abnormally prolong sodium channel opening in nerve membranes.⁶³ This influx of sodium is antagonized by the presence of TTX.⁴⁰

In vitro studies have also shown that scaritoxin causes release of norepinephrine and acetylcholine and increases sodium channel permeability.⁴⁶⁰ Maitotoxin as well may trigger release of norepinephrine and stimulate cellular uptake of calcium and has been hypothesized to stimulate cholinergic receptors by inhibiting acetylcholinesterase.^40,428 However, evidence suggests that highly purified ciguatoxin preparations may not have anticholinesterase effects in vivo.²⁸⁰

Hypertension occurring with ciguatera can be suppressed in animal models with phentolamine (an α-antagonist), suggesting α-adrenergic receptor activity. Although purified ciguatoxin appears to have cardiac stimulatory effects (increasing heart rate and output), maitotoxin is a myocardial depressant in vitro, which may explain the variation in clinical presentation. Isolated human atrial trabeculae show concentration-dependent positive inotropy with CTX-1 that is not reversed with mannitol.²⁸⁵ Cardiac calcium conduction effects have been implicated in the activity of maitotoxin, because its action is inhibited in the presence of verapamil, magnesium ions, or low-calcium-concentration solutions. In mice, injection of maitotoxin can induce marked increase in total calcium content of the adrenal glands and rise in plasma cortisol concentration.⁴⁶⁴ When injected into mice, ciguatoxin targets the heart, adrenal glands, and autonomic nervous system.⁴⁶⁶ Ciguatoxin and CTX-4c (a derivative), administered in repeated doses, cause the mouse heart to suffer septal and ventricular interstitial fibrosis, accompanied by bilateral ventricular hypertrophy.⁴⁶⁸ Ciguatoxin is a potent substance, with an LD₅₀ in mice of 0.45 mg/kg in purified form. Maitotoxin is even more potent, with an LD₅₀ of 0.13 mg/kg in mice. It is interesting to note that ciguatoxins can become toxic to fish in higher concentrations, thus potentially limiting the levels of these compounds carried by a fish.²⁸⁴ However, the toxin or toxins may reside in the skeletal muscle or other tissues of the fish in association with proteins that may be protective of the carrier.¹⁹⁰

All identified toxins associated with ciguatera are unaffected by freeze-drying, heat, cold, and gastric acid and do not affect the odor, color, or taste of the fish. There is some evidence that cooking methods can alter the relative concentrations of the various toxins. For example, boiling fish flesh will remove water-soluble toxins, but frying or grilling the flesh may increase toxicity of lipid-soluble toxins as a result of releasing lipid-soluble components from the cellular compounds to which they are normally bound.¹³⁶

Clinical Presentation

CFP is associated with gastrointestinal, cardiovascular, neurologic, and neuropsychiatric symptoms and signs. The meal containing ciguatoxins is generally unremarkable in taste and smell. Symptoms may develop within minutes of ingestion, although they generally occur within 2 to 6 hours after the meal. Almost all victims develop symptoms by 24 hours.^26,138 The severity of symptoms seems to follow a dose-dependent pattern, with victims who eat larger portions of ciguatoxic fish experiencing more severe symptoms (Box 72-7). Additionally, there are variable concentrations of ciguatoxin within a fish, depending on the fish size, age and part consumed, with higher concentrations in the viscera, especially the liver, spleen, gonads, and roe.^257,273

The most common initial symptoms reported in cases of ciguatera include acute gastroenteritis, with abdominal cramps, nausea, vomiting, and diarrhea.²⁶ These symptoms rarely persist for longer than 24 hours but may require fluid resuscitation.¹³⁸ Myriad other symptoms reported in ciguatoxic patients are listed in Box 72-7. Headache is a common symptom, and victims often complain of experiencing a metallic taste. In a well-described clinical outbreak affecting a group of scuba divers who consumed coral trout (Cephalopholis miniatus), the most common symptoms were weakness, cold sensitivity, paresthesias, a taste sensation of carbonation, and myalgias.² Two men suffering from ciguatera poisoning had painful ejaculation with urethritis, which in turn may have induced dyspareunia (pelvic and vaginal burning) in their female partners after intercourse.²⁷¹ In a North Carolina outbreak in 2007, six of the seven sexually active patients reported onset of painful intercourse beginning in the first few days after the onset of illness. Although sexual transmission of ciguatoxin has been documented, painful intercourse as a consequence of ciguatera fish poisoning is not commonly described.²⁷³ Neurologic symptoms seem to develop after initial gastrointestinal symptoms. Paresthesias and myalgias are typically seen within the first 24 hours and usually resolve by 48 to 72 hours after ingestion of ciguatoxins, although there have been reports of neurologic symptoms persisting for weeks to months.^{27,277,362,273}

Many case reports of ciguatera describe symptoms of a sensory perception of “hot and cold reversal,” and loose, painful teeth. Although presence of these symptoms is suggestive of ciguatera, their absence does not exclude possibility of the disease.²⁷ There have also been reports of a paradoxical reversal of temperature perception, resulting in cold feeling hot, rather than hot feeling cold.²⁷ However, other reports demonstrated that gross temperature discernment remains intact and the description of paradoxical heat perception may be misleading.⁶² These authors describe the symptoms as intense, painful tingling or “electric shock” rather than true reversal of hot and cold perception.⁶² This peculiar symptom may have a delay in onset of 2 to 5 days, may last for months after ingestion, and is otherwise seen only with neurotoxic shellfish poisoning (brevetoxins), caulerpicin (from the green alga Caulerpa) toxicity, or turban shell poisoning.^128,525 These symptoms are commonly associated with a polyneuropathy, predominately affecting sensory small fibers.⁴⁰³ Pruritus is another vague but often described sensation in victims of ciguatera. Onset of pruritus may be delayed for more than 24 hours but is rarely, if ever, seen in the absence of other symptoms.^148,277 Pruritus may persist for weeks and be exacerbated by any activity that increases skin temperature (blood flow), such as exercise or alcohol consumption.²⁷⁷ Ciguatera-associated pruritus may occasionally become severe and may improve after treatment with histamine receptor antagonists. Delayed symptoms also include hiccups.

Tachycardia and hypertension are often described in ciguatera poisoning, in some cases after transient bradycardia and hypotension, which can be severe.⁸⁷ Hallucinations, flushing, flaccid paralysis, and fever occur but are uncommon. More severe reactions tend to occur in persons previously stricken with the disease. Severely affected persons may report intermittent symptoms for up to 6 months, with a gradual diminution in frequency and intensity. There may be some regional variability to the symptoms of presentation.^27,324 Reappearance or worsening of symptoms after alcohol consumption has been described.²⁷³ Other foods and behaviors associated with symptom recurrence include nuts, caffeine, port wine, chicken, other fish, and physical activity/exertion.¹⁵⁵ Persons who have ingested parrotfish (scaritoxin) have been reported to suffer from classic ciguatera poisoning, as well as a second phase of toxicity 5 to 10 days after the initial onset, consisting of ataxia, dysmetria, and a resting or kinetic tremor.⁹⁴ Although both gastrointestinal and neurologic effects are the hallmarks of ciguatera intoxication, there are regionally dependent differences in clinical presentation. Neurologic effects predominate in the Indo-Pacific region, whereas gastrointestinal symptoms predominate in the Caribbean.²¹⁹ Consumption of Indian Ocean fish has led to a further syndrome characterized by hallucinations, incoordination, loss of equilibrium, depression, and nightmares. Sensitization with repeated exposure has been described, leading to more rapid onset of effects.²¹⁹

Whether ciguatoxin crosses the placenta is not known, but exposures during pregnancy have resulted in normal fetal outcomes.⁴¹³ Transmission via breast milk has been reported.²⁴⁸ In small children, symptoms of ciguatera poisoning may be no more specific than irritability, sleep disturbance, nausea, and vomiting.⁵⁰⁸ Other reported symptoms include carpopedal spasm, ptosis, and inconsolability.

An overall death rate of 0.1% to 12% has been reported with ciguatera, but the lower percentage seems more likely with modern supportive care. Death is usually attributed to respiratory paralysis.²³⁷

Diagnosis

The diagnosis of ciguatera poisoning is based on clinical symptoms. Differential diagnosis includes paralytic shellfish poisoning, eosinophilic meningitis, type E botulism, organophosphate insecticide poisoning, TTX poisoning, and psychogenic hyperventilation.^27,391 Temperature-related dysesthesia has also been reported in neurotoxic shellfish poisoning (NSP) from consumption of shellfish contaminated with brevetoxin. Therefore, NSP should be considered in the differential diagnosis. Unreliable folklore used in the past to aid in predicting ciguatoxic seafood includes the advice that a lone fish (separated from the school) should not be eaten. Other myths include ants and turtles refuse to eat ciguatoxic fish, that a thin slice of ciguatoxic fish does not show a rainbow effect when held up to the sun, and that a silver spoon tarnishes in a cooking pot with ciguatoxic fish.¹⁰⁰ Ciguatoxin may be detected in the flesh of fish by two immunoassay techniques, a mouse bioassay where a sample of the fish is injected intraperitoneally into a mouse, and a rapid IgG assay.²⁰⁹ Rapid immunoassays have largely replaced using mice and other archaic tests (e.g., feeding fish to a mongoose or cat to observe for neurologic symptoms or death). HPLC is also available for ciguatoxins and okadaic acid. Unfortunately, tests for ciguatoxin are still of limited clinical benefit because most institutions do not have the equipment needed for their performance. Also, multiple individuals presenting with the same symptomatology that is consistent with CFP after consuming the same fish strongly supports the diagnosis.

Treatment

If possible, a piece of the implicated fish should be obtained in the event that analysis for ciguatoxins can be performed. Treatment of ciguatera poisoning is primarily supportive. Intravenous hydration with crystalloid and electrolyte replacement may be necessary for dehydration. Severe or refractory hypotension may require a vasopressor. Antiemetics such as ondansetron may be beneficial. Atropine has been shown to be effective in patients with symptomatic bradycardia or excess cholinergic stimulation.¹⁴⁸ Gastric decontamination is rarely indicated, because presentation is usually delayed and gastroenteritis has already occurred. Activated charcoal may bind some of the toxin in the gastrointestinal tract, but this is not useful when presentation is more than 1 to 2 hours after exposure.

Many traditional remedies have been used for centuries to treat ciguatera. Edrophonium, neostigmine, corticosteroids, pralidoxime, ascorbic acid, pyridoxine (vitamin B₆), salicylic acid, colchicine, and vitamin B complex have all been tried with variable success; however, there is no current clinical support for these modalities.³²⁴ Local anesthetics (e.g., lidocaine, tocainide) have also been administered for treatment of ciguatera.^64,270 These agents are effective blockers of sodium influx and may antagonize the sodium channel effects of ciguatoxin. In addition, amitriptyline has been used for its sodium channel blocking effects, as well as its potent antimuscarinic effects.^54,59,114 Nifedipine has been used to counteract the cellular uptake of calcium caused by maitotoxin, and to relieve headache.⁵⁹ Although there is limited experience with most of these therapies, they may be beneficial in cases refractory to supportive care alone.

Mannitol has become the most widely applied therapy in severe cases of ciguatera poisoning.^52,444 Most reports of its success are based on limited data with small numbers of patients.^{131,354,359,509} One series described successful treatment with mannitol in 24 victims of ciguatera poisoning. Each was infused with up to 1g/kg of a 20% mannitol solution intravenously over 30 minutes. None of the victims received more than 250 mL.³⁵⁴ The mechanism by which mannitol might be effective in abating the neurologic symptoms from ciguatera poisoning is unknown, but suggested theories have included acting as a free radical scavenger, competitive inhibitor of ciguatoxin at the cell membrane, and promoting a decrease in Schwann cell edema.^359,509 It is also possible that the osmotic action of mannitol may render ciguatoxin inert.^354,359 Curiously, mannitol therapy seems to have no beneficial effect on mice administered a sublethal intraperitoneal dose of ciguatoxin (CTX-1).²⁸⁹ A more recent double-blinded, randomized study on mannitol therapy found no difference in resolution of symptoms when compared with saline.⁴⁰³ Of note, therapy was not initiated until an average of 19 hours after exposure in the mannitol group and 40 hours after exposure in the saline group. In humans, the empiric observation is that mannitol has greater benefit if administered early in the course of illness, so the delay may have diminished the effect in this study. One concern with administration of mannitol in the setting of ciguatera is that patients may present dehydrated. In these cases, patients should be adequately rehydrated before administration of mannitol. During recovery from ciguatera, it is recommended that victims exclude fish, shellfish, alcoholic beverages, and nuts and nut oils from their diet, as these could result in an exacerbation of the syndrome.⁴²⁷ Gabapentin has been used successfully in the treatment of chronic symptoms after ciguatera poisoning, but symptoms seem to recur after cession of therapy in some patients.³⁶²

Prevention

For travelers, common sense dictates avoiding any fish that local fishermen and residents do not eat, or fish caught in areas known to be endemic for ciguatera. Any level of Caribbean ciguatoxin ≥0.1 ppb of fish tissue is thought to be a health risk.²⁷³ Because of the accumulation of toxin, all oversized fish of any predacious reef species (such as jack, snapper, barracuda, grouper, or parrot-beaked bottom feeder) should be suspected to be toxic. Moray eels should never be consumed. Internal organs of implicated fish seem to concentrate the toxin and should therefore be avoided. Natural events, such as hurricanes and earthquakes, have been associated with increased incidence of ciguatera, presumably because of reef disturbance. El Niño storms may also affect the incidence of ciguatera in the Pacific.²⁹

Pathophysiology

The benthic dinoflagellate O. siamensis was presumed to be the probable toxin source.^352,524 As with ciguatoxin, the poison typically does not impart any unusual appearance, odor, or flavor to the fish. The exact mechanism of PTX toxic effects remains to be elucidated. However, in vitro studies have demonstrated multiple effects. PTX appears to increase cell permeability to sodium in neuronal cells by converting the sodium-potassium ATPase pump to a permeable channel to monovalent cations, allowing potassium efflux and sodium influx. The subsequent membrane depolarization may open voltage-dependent calcium channels in synaptic nerve terminals, cardiac cells, and smooth muscle cells. Additionally, there is increased intracellular calcium concentration through the sodium–calcium exchanger. Ultimately, the increase in intracellular calcium stimulates release of neurotransmitters from nerve terminals, histamine from mast cells, and vasoactive agents from the vascular endothelium.^343,501 PTX may also increase cytosolic hydrogen concentration.⁵⁰¹

Clinical Presentation

Symptoms of palytoxin exposure vary greatly, depending on the route of exposure. This was originally described using several animal species and various routes of exposure.⁵⁰⁶ Deaths have occurred due to PTX injection in animals and ingestion in humans. However, a variety of additional symptoms have been observed to be caused by dermal, ocular, and inhalational exposure in humans. Ingestion in humans reportedly causes abdominal cramps, nausea, diarrhea, limb paresthesias, muscle spasm, and respiratory distress. Of this cluster of symptoms, the predominant physical findings appear to be respiratory distress and extreme tonic muscle contractions. Severe debility leading to death may occur within 15 minutes of the onset of symptoms.¹⁹⁴ Mortality has been reported to be as high as 45%. One of the most commonly reported complications appears to be rhabdomyolysis, with peak creatine kinase levels typically occurring 24 to 36 hours after symptom onset.^115,349 A postmortem examination in one case after ingestion of Sardinella marquesensis (Marquesan sardine) flesh and viscera demonstrated enterocolitis and the sequelae of hypotension and acute heart failure.³¹⁶

Inhalational exposure has also been described. In the summer of 2005, a massive proliferation of the tropical microalga Ostreopsis spp. broke out along the Mediterranean coastline of Liguria, near Genoa, Italy. Approximately 200 people experienced fever, conjunctivitis, and respiratory distress after exposure to this marine aerosol. Palytoxin and a new analog, ovatoxin-A, were later identified.⁹⁵ Dermal exposures have also been described, specifically with handling of PTX-containing marine zoanthids sold in the home aquarium trade.^210,343 There is a great deal of conflicting information regarding the risks of PTX exposure from store-bought aquarium zoanthids. Numerous unconfirmed anecdotal stories can be found by affected individuals online at coral reef hobbyist forums. PTXs are not found in all commercially available zoanthid species, but clearly occur in potentially dangerous concentrations in a select few.¹¹⁵

Treatment

Therapy is supportive and based on symptoms, with focus on aggressive hydration to prevent renal failure associated with rhabdomyolysis. Because of the severe nature of the intoxication, early gastric emptying is desirable; however, the disease is so unusual and so rarely suspected (because of a lack of history) that gastric emptying is not often considered. Aggressive management and early intensive care are essential.

Prevention

Clupeotoxic fish should be avoided, especially during summer months. These fish are indigenous to the Caribbean, African coastal, and Indo-Pacific waters. The viscera of suspicious fish can be fed to experimental animals to see if an illness is generated. Because a rapid and sensitive hemolysis neutralization assay for palytoxin is available, its presence in toxic seafood should become easier to determine.⁴¹ Persons handling zoanthid coral should wear protective gloves to decrease the risk of local and systemic toxicity.

Pathophysiology

The major toxin sources of PSP include marine dinoflagellates of the genera Alexandrium (formerly Gonyaulax), Gymnodinium, and Pyrodinium. Bacterial origins of the toxin have also been proposed.¹⁴⁰

Dinoflagellates produce a number of toxins, the most commonly identified of which is saxitoxin. If a single organism predominates, it can discolor the water, creating a black, blue, pink, red, yellow, brown, or luminescent “tide.”⁹⁶ Organisms can multiply rapidly from a concentration of 20,000/L to more than 20 million/L. These plankton can release massive amounts of toxic metabolites into the water, at times leading rapidly to enormous mortality in various bird and marine populations, including large mammals such as dolphins and even whales. Large numbers of dead animals on the beach suggest a colored tide. The trend to increased numbers and magnitude of blooms is empirically attributable to many factors, including coastal development, dumping of sewage, fertilizer runoff, and ocean warming. Kills by the dinoflagellate Ptychodiscus (formerly Gymnodinium) brevis are estimated at 100 tons of fish per day. The problem is markedly increasing in Europe.⁴⁸⁸

A limited number out of the approximately 1200 species of dinoflagellates has been implicated in human toxic syndromes.⁴⁰¹ PSP has been linked to the dinoflagellate Protogonyaulax, species catanella (U.S. Pacific coast) species tamarensis var. excavata (U.S. Atlantic coast and Europe), and Gymnodinium catenatum (northwestern Spain).^312,461 These creatures are relatively fastidious and prefer to bloom in warm, sunlit water of low salinity. Some algal organisms may release their toxin in the form of microscopic cysts, which can overwinter at the sediment–water interface. In mollusks, the greatest concentration of toxin is found in the digestive organs (e.g., the dark hepatopancreas), gills, and siphon.⁴¹⁵ Toxic benthic dinoflagellate cysts may be transported by dredging operations, potentially introducing a dinoflagellate population into a new region.⁵³⁰

Although the origin of PSP toxins is assumed to be dinoflagellates, the toxins have been isolated in both marine and freshwater bivalves that are not associated with dinoflagellates. It has not been determined how this has occurred.³⁴⁶ The bacterium Moraxella isolated from Protogonyaulax tamarensis has been shown to produce PSP toxins in culture. Toxin production can increase in nutritionally deficient environments.²⁵⁹

The paralytic shellfish toxins identified to date are 18 related tetrahydropurine compounds produced mainly by dinoflagellates of the genus Alexandrium. These include saxitoxin, neosaxitoxin, and the gonyautoxins (GTX1, GTX2, GTX3, GTX4, GTX5), with the best characterized being saxitoxin.¹⁶¹ Saxitoxin (C₁₀H₁₇N₇O₄) takes its name from Saxidomus giganteus, the Alaskan butter clam. P. brevis is a toxic dinoflagellate that produces a milder toxin. Other dinoflagellates considered poisonous to animals or humans include Gonyaulax acatenella, Pyrodinium phoneus, Pyrodinium bahamense var. compressa, Gonyaulax monilata, Gonyaulax polyhedra, Gymnodinium veneficum, and Exuviaella ariae-lebouriae.³⁵³ S. giganteus and the Washington clam (Saxidomus nuttalli) may carry the toxin in their neck parts for up to 2 years; however, no physical characteristic distinguishes a carrier animal.

Unfortunately, a direct human serum assay to identify the toxin responsible for PSP is not readily available to clinicians. PSP is assessed in foodstuff using a mouse bioassay, in which a 20-g mouse is injected with 1 mL of an acid extract of the shellfish, and the time taken for the animal to die is recorded. One mouse unit (mu), or 0.18 mg, is the amount of injected saxitoxin that kills a test mouse in 15 minutes.⁴⁸⁸ In most countries, the action level for closure of a fishery is 400 mu/100 g shellfish. Polyclonal enzyme-linked immunosorbent assays (ELISAs) that measure saxitoxin, neosaxitoxin, and gonyautoxins 1 and 3 may be refined soon as reasonable screening techniques. Other testing methods under investigation include a sodium channel–blocking assay, spectrometry, thin-layer chromatography, and fluorometric HPLC.^161,300 An automated tissue culture (neuroblastoma cell) bioassay may become a valid alternative to live animal testing.²³³

Saxitoxin (STX) and related compounds are water-soluble and heat and acid stable. At least 24 saxitoxin-like congeners have been identified with an array of hydroxyl, carbamyl, and sulfate substitutions on the backbone structure, also with large variation in potency.^191,140 Like TTX, they can be destroyed to a certain extent in an alkaline medium but not by ordinary cooking. Saxitoxins are chemically distinct from TTX, but both act on site 1 of the voltage-dependent sodium channel, blocking influx of sodium into excitable cells and restricting signal transmission along nerve and muscle membranes.²⁶⁸ Although the threshold levels for causing illness in humans are not definitively known, it has been suggested that ingestion of 200 to 500 mg would cause at least mild symptoms; 500 to 2000 mg, moderate illness; and more than 2000 mg, serious or fatal illness. However, serious symptoms have been reported after ingestion of less than 100 mg of saxitoxin in adults. During peak red tide seasons, each mussel may accumulate up to 50,000 mu of saxitoxin. Mussel concentrations of saxitoxin have been determined to be too high for consumption when seawater dinoflagellate counts are as few as 200/mL.⁴¹⁵ A saxitoxin concentration of greater than 75 to 80 mcg/100 g foodstuff is considered hazardous to humans. In the 1972 New England red tide, the concentration of saxitoxin in blue mussels exceeded 9000 mg/100 g foodstuff. After cases of PSP in Massachusetts, saxitoxin concentrations of 24,400 mg/100 g were recorded in raw mussels. With oral ingestion of saxitoxin, the LD₅₀ for mice is 263 mg/kg. It has been estimated that as little as 0.5 to 1 mg of saxitoxin can be fatal in humans.⁴¹⁵

Neither steaming nor cooking affects the potency of the toxin. Commercial processing of shellfish does not eliminate the toxin or the potential for toxicity; therefore, public health agencies in the United States and Canada strictly monitor these canning industries.

Clinical Presentation

The onset of symptoms of paralytic shellfish poisoning is rapid. Within 30 to 60 minutes of ingesting toxic shellfish, victims complain of paresthesias, numbness, vertigo, and tingling of the face, tongue, and lips. Cranial nerve dysfunction, including dysarthria, dysphonia, dysphagia, and even blindness, can occur.^{168,192,214,312} Other early symptoms include lightheadedness, floating sensation, ataxia, weakness, hyperreflexia, incoherence, sialorrhea, thirst, abdominal pain, nystagmus, dysmetria, headache, diaphoresis, sensation of loose teeth, chest pain, and tachycardia. Neurologic symptoms progress to involve the extremities and trunk over the first 1 to 2 hours. Weakness of the limbs may begin anytime after the sensory changes, and gradually progresses to ataxia, inability to use the extremities, and finally paralysis. Reflexes are frequently normal throughout progression of the disease, and patients remain awake and alert. Death results from respiratory failure with diaphragmatic and chest wall muscle paralysis.

Although some victims have nausea, vomiting, or diarrhea, lack of gastroenteritis and thus early self-decontamination may in part explain why mortality from PSP approaches 25% in some older series.^26,505 More recent reports cite a lower incidence of fatalities, probably because of improvements in supportive care. Hypotension can result from direct action of the toxin on vascular smooth muscle, although both diastolic and systolic hypertension have been reported.^242,167 Toxicity is generally not delayed more than 10 to 12 hours, with a median onset of 3 hours. Prognosis is good for individuals surviving past 12 hours, but weakness can persist for weeks after recovery. Children seem to be more sensitive to saxitoxin than are adults. In milder cases, alcohol ingestion appears to increase toxicity. Saxitoxin is very similar structurally to TTX and shares a common mechanism of action. Intoxication causes superimposable symptoms, and these two syndromes can be differentiated only by their area of distribution or by isolation and identification of the specific toxin.¹⁴⁵

Treatment

No antidotes are currently available for saxitoxin or paralytic shellfish poisoning. The victim should be closely observed in the hospital for at least 24 hours for respiratory insufficiency. Airway patency and respiratory support are of utmost importance, and even patients with severe symptoms of PSP often do well if expeditiously supported with mechanical ventilation. Although gastric emptying has been advocated by some authors when shellfish suspected of containing saxitoxin are ingested, airway collapse can be rapid and induction of emesis should not be attempted.²¹⁴ These toxins bind well to charcoal, and an oral dose of charcoal should be administered if this can be done safely.⁸⁵ Some clinicians suggest that atropine administration may worsen symptoms of PSP and should be avoided, because saxitoxin and its derivatives may have antimuscarinic effects.⁴¹⁴ Several studies have suggested that acidity may enhance the potency of saxitoxin, leading some authors to speculate that serum alkalinization might be of benefit to victims, although the efficacy of this practice has yet to be established.^{9,203,307,356}

At least one human case report and some animal data have implied that dialysis or hemoperfusion may benefit some victims of severe PSP.^26,377 Other reports are less optimistic, as in vitro trials have demonstrated that dialysis is not effective in removing saxitoxin.^132,203 Some clinicians have suggested enhancing renal clearance with diuresis, but no study supports this practice. Maintaining normal urine output should suffice in most cases.

Prevention

The most important aspect of managing PSP is prevention. Although leeching of shellfish in freshwater for several weeks followed by vigorous cooking may remove up to 70% of the toxin, such procedures are recommended only for persons stranded on desert islands. It has been said that one should not eat shellfish in the northern hemisphere in months that contain the letter r. It has become more apparent with changing ocean conditions that shellfish in many parts of the world may be contaminated throughout the year because of high water concentrations of Gonyaulax. Most coastal agencies monitor dinoflagellate concentrations off the shores of developed countries and restrict shellfish harvesting during high-risk periods. In addition, harvesting management strategies, such as harvesting parts of the organisms known to be safe and discarding the parts of the organism that may pose a threat, are in place.¹⁴⁰ Many outbreaks of this illness have occurred on isolated islands where public health monitoring is infrequent and intensive care medicine resources scarce. Saxitoxin found in southern puffer fish off the coast of Florida is much more concentrated within the muscle than in the liver; therefore, even careful preparation of these puffer fish fillets would not prevent intoxication to consumers.²⁶⁸

Pathophysiology

Domoic acid was first isolated in 1958 following investigations on the antihelmintic and insecticidal activity of seaweed extracts. After the 1987 epidemic of neurotoxic illness in Price Edward Island, Canada, significant evaluation of the surviving victims was undertaken. Chemical analysis at various laboratories ruled out all other known toxic causes of the symptoms displayed by patients.⁵²¹ Intraperitoneal injection of extracts of implicated mussels into mice produced a syndrome characterized by reproducible scratching followed eventually by death.^363,463 The toxin was finally identified as domoic acid.

Domoic acid is a water-soluble, excitatory neurotransmitter and a glutamate receptor agonist. It is structurally related to kainic acid, a potent neurotoxic amino acid.^{351,408,463,521} This group of compounds is excitatory and acts on three types of receptors in the central nervous system (CNS), with those in the hippocampus being the most sensitive. Domoic acid seems to work by activating kainate receptors in the brain more potently than does kainic acid itself. The result of this stimulation is extensive damage to the hippocampus in victims of the poisoning, as well as less severe injury to portions of the thalamic and forebrain regions.^312,387,463 There may also be non-N-methyl-D-aspartate (NMDA) mediated mechanisms.⁴⁵⁹

It was estimated that the mussels implicated in the Canadian outbreak of ASP contained a total amount of domoic acid in excess of 6 kg, with most being concentrated in the digestive glands.^178,521 Other organisms known to produce domoic acid include the phytoplankton Alsidium corallinum and C. armata. Subsequent research suggests that other phytoplankton, such as Amphora coffeaeformis, can also produce domoic acid. Scientists continue to monitor shellfish and marine microorganisms to determine the presence of other sources. There are 10 isomers of DA identified to date; however, some of these have significantly lower toxicity than does the parent compound.²⁷⁹ Domoic acid is relatively stable and does not degrade at room temperature. Also, cooking will not increase the safety of the shellfish product if contaminated with DA.³¹¹ There is wide variation in tissue distribution and retention of DA; for example, razor clams have been shown to retain DA for up to a year and contain DA throughout all tissues, whereas a majority of the toxin is confined to the viscera in mussels and fish.²⁷⁹

Clinical Presentation

As a result of the Prince Edward Island event, numerous laboratory-based toxicity studies were performed in order to characterize the toxicity of DA. Multiple regimens that have been investigated include intraperitoneal, intravenous, intraarterial, intrauterine, and oral dosing and direct brain injections, making a direct comparison of DA toxicity between species difficult. Studies have been performed in monkeys, mice, rats, birds, and fish. The most notable clinical signs of toxicity include scratching and seizures in rodents, vomiting in monkeys, spiral-swimming in fish, and tremors and scratching behavior in birds.^279,363,335

Humans involved in the Canadian epidemic of amnestic shellfish poisoning had initial symptoms of nausea, vomiting, abdominal cramps, and diarrhea 1 to 24 hours after ingestion.^363,463 Neurologic symptoms initiated with memory loss began within 48 hours after ingestion and progressed in some victims to seizures, hemiparesis, ophthalmoplegia, and coma. Some victims displayed purposeless grimacing and chewing. Follow-up neuropsychological testing on affected patients displayed predominantly an anterograde memory disorder, with most other cognitive functions preserved.³⁶³ The most severely affected individuals also had some retrograde amnesia. Labile blood pressure and cardiac dysrhythmias were recorded in a few individuals, suggesting DA may be cardiotoxic.³⁷¹ Elevations in blood urea nitrogen (BUN) and creatine phosphokinase were also noted in many victims and have been recorded in animals suffering DA poisoning, possibly resulting from exertional myopathies or tremors.^363,519

The onset of symptoms in victims of the Prince Edward Island epidemic ranged from 15 minutes to 38 hours, with the average approaching 5 hours.^363,463 Increased age was identified as a risk factor for both the severity of illness and memory loss. Males were found to be more susceptible.³⁷¹ Most fatalities occurred in the oldest victims, with postmortem findings suggesting neuronal loss or necrosis, accompanied by astrocytosis.³⁶³ The most severe damage was to the hippocampus and amygdala, which are areas of the brain participating in memory functions. Lesions were also noted in the claustrum and the septal and olfactory regions. Retinal lesions have also been reported.³⁷¹ No lesions were found in the motor nuclei of the brainstem. Hippocampal lesions in victims at autopsy resembled those seen in the brains of animals injected with kainic acid.^363,312,432 A follow-up study on patients from the Montreal area suggested that bronchial secretions became so profuse in the hours after mussel ingestion that one-half of the severely affected individuals required endotracheal intubation.³⁶³ Pupillary dilation or constriction, and piloerection were also common findings. Approximately 10% of the involved patients demonstrated either persistent memory loss or other neuropathies. Of patients exhibiting neurologic toxicity, maximal effects were noted within the first 3 days after mussel ingestion, and maximal improvement in neurotoxicity occurred in 24 hours to 12 weeks after ingestion. Four and 6 months postexposure, several patients had distal atrophy with weakness of the extremities and hyporeflexia. Electromyography findings were consistent with an acute nonprogressive neuronopathy involving anterior horn cells or diffuse axonopathy predominantly affecting motor axons.³⁷¹

Treatment

As with most other shellfish toxins, no antidote exists for amnestic shellfish poisoning. Based on the alleged mechanism of action of both domoic and kainic acid, it is possible that benzodiazepines may be beneficial in controlling some of the excessive hippocampal activity and seizures.^351,519 Animal studies have suggested a lowered mortality in groups in which benzodiazepines are used after domoic acid exposure. There may also be a role of NMDA antagonists.³⁸

Prevention

Many regulatory agencies worldwide have established biotoxin monitoring programs. Although monitoring programs have been effective at preventing human toxicity, chronic DA toxicity has been characterized in other mammalian species such as sea lions.²⁷⁹ To protect seafood consumers, authorities have established an action limit for DA of 20 mcg DA/g shellfish tissue. This is based on retrospective estimations of DA concentrations of 200 mcg DA/g mussel, which caused illness during the ASP outbreak and incorporates a safety factor of 10. This regulatory limit has been adopted by the United States, European Union, New Zealand, and Australia. Levels exceeding this limit trigger closure of the affected beaches and shellfish harvesting areas.²⁷⁹

Pathophysiology

The producing organism was originally thought to be Protoperidinium crassipes. However, it is now known to be produced by the small dinoflagellate Azadinium spinosum.²³⁹ Limited availability of the pure toxins has impeded the necessary investigations of AZP. Initially, AZA1 was isolated from the Killary mussels. Investigations have shown that AZA1 is cytotoxic to many cell types, including liver, lung, pancreas, thymus, spleen, and especially small intestine. These effects are time and concentration dependent.⁴⁸⁴ There has been identification of several analogs of AZA. Some studies indicate that AZAs might have different targets. For example, AZA4 inhibits plasma membrane calcium channels.¹⁵⁸

Clinical Presentation

The symptoms of AZP appear within hours of ingestion and include nausea, vomiting, severe diarrhea, and stomach cramps. The illness persists for 2 to 3 days. To date, no long-term effects have been reported.⁴⁸⁴ Most information regarding AZA toxicology has been obtained from in vitro and in vivo experiments. Mice injected with low doses of AZA developed slowly progressive paralysis, difficulty breathing, and listlessness. Large oral doses in mice demonstrated widespread organ damage, particularly necrosis in the lamina propria within the small intestine.¹⁵⁸ AZP remains a rare illness, although it is likely that there is underreporting because of the short duration and benign coarse of illness.

Diagnosis

Levels of AZA vary significantly among mussels harvested from a given region. The European Commission regulatory limit is 0.16 mg/kg shellfish. Previous reports have determined the presence of AZA by liquid chromatography–mass spectrometry/mass spectrometry.²⁵⁴ Other detection methods, such as ELISA, have been developed for AZA but are not commercially available.⁴⁸⁴

Treatment

At present, there is no specific treatment for AZP. Treatment is primarily supportive, with focus on hydration to prevent dehydration and antiemetics.

Prevention

Several incidents of human intoxication were the impetus for implementation of a national surveillance program that monitors weekly the levels of AZA in shellfish from all production areas in Ireland. There have since been no further reports of AZP incidents associated with Irish shellfish. In 2008, an outbreak occurred in France and Ireland following accidental dispatch to consumers of AZA-contaminated shellfish that were held in quarantine following AZA confirmation.¹⁵⁸