Fish Neurotoxins: Understanding Ciguatera, Tetrodotoxin, and Scombrotoxin Poisoning

17.08.202319.07.2023 by alexxlab

How do fish neurotoxins affect human health. What are the symptoms of ciguatera poisoning. How can you prevent pufferfish poisoning. What causes scombroid poisoning in fish. Where is the risk of fish toxin exposure highest. How are different types of fish poisoning treated. Why are certain fish species more likely to contain harmful toxins.

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The Hidden Dangers of Fish Neurotoxins

Fish neurotoxins pose a significant health risk to consumers worldwide, particularly in tropical and subtropical regions. These naturally occurring biotoxins can cause severe poisoning even when fish are properly cooked. Understanding the types, sources, and effects of these toxins is crucial for both travelers and seafood enthusiasts.

Types of Fish Neurotoxins

There are three primary types of fish neurotoxins that cause poisoning in humans:

Ciguatoxin (causing ciguatera fish poisoning)
Tetrodotoxin (associated with pufferfish poisoning)
Scombrotoxin (leading to histamine poisoning)

Each of these toxins has unique characteristics, sources, and effects on the human body.

Ciguatera Fish Poisoning: A Tropical Threat

Ciguatera fish poisoning is the most common form of fish-related neurotoxin poisoning, particularly in tropical and subtropical waters. It occurs when humans consume fish that have accumulated ciguatoxins through their diet.

High-Risk Fish Species for Ciguatera

Which fish species are most likely to cause ciguatera poisoning? The following fish are known to pose a higher risk:

Groupers
Barracudas
Moray eels
Sturgeon
Sea bass
Red snapper
Amberjack
Mackerel
Parrotfish
Surgeonfish
Triggerfish

The CDC strongly advises against consuming moray eel or barracuda due to their high risk of containing ciguatoxins.

Geographical Distribution of Ciguatera Risk

Where is the risk of ciguatera poisoning highest? The toxin is prevalent in reef fish from:

The West Indies
The Pacific Ocean
The Indian Ocean

In the United States, cases have been reported in Hawaii, Guam, Puerto Rico, the U.S. Virgin Islands, and Florida. Isolated incidents have even occurred along the eastern seaboard.

Symptoms of Ciguatera Poisoning

How quickly do ciguatera poisoning symptoms appear? Symptoms typically manifest between a few minutes to 6 hours after consuming contaminated fish. The most common symptoms include:

Gastrointestinal issues (nausea, vomiting, diarrhea)
Neurological abnormalities (tingling sensations, numbness)
Cardiovascular problems
Muscle pains
Dizziness
Temperature sensation reversal

In severe cases, irregular heart rhythms and low blood pressure may occur. Symptoms can persist for several days to up to 4 weeks.

Treatment for Ciguatera Poisoning

How is ciguatera poisoning treated? Currently, there is no specific antidote for ciguatoxin. Treatment focuses on:

Relieving symptoms
Managing complications
Supportive care

Recovery typically takes several days to several weeks, depending on the severity of the poisoning.

Tetrodotoxin: The Deadly Pufferfish Poison

Tetrodotoxin, also known as pufferfish poisoning or fugu poisoning, is a rare but potentially fatal form of fish poisoning. It is primarily associated with the consumption of pufferfish from Indo-Pacific waters.

Geographical Distribution of Tetrodotoxin Risk

Where is tetrodotoxin poisoning most common? While predominantly linked to Indo-Pacific pufferfish, cases have been reported from:

The Atlantic Ocean
The Gulf of Mexico
The Gulf of California

Japan continues to face challenges with pufferfish poisoning due to the popularity of fugu in its cuisine.

Symptoms of Pufferfish Poisoning

What are the signs of tetrodotoxin poisoning? Symptoms typically appear between 20 minutes and 3 hours after consuming poisonous pufferfish and may include:

Numbness of lips, tongue, face, and extremities
Sensations of lightness or floating
Headache
Nausea and vomiting
Abdominal pain
Diarrhea
Slurred speech
Difficulty walking
Extensive muscle weakness
Convulsions
Respiratory distress
Mental impairment
Cardiac arrhythmia

Tetrodotoxin poisoning can be fatal within 4 to 6 hours, making immediate medical attention crucial.

Treatment for Pufferfish Poisoning

How is tetrodotoxin poisoning managed? Treatment strategies include:

Limiting toxin absorption
Alleviating symptoms
Treating life-threatening complications

Currently, there is no known antidote for tetrodotoxin, emphasizing the importance of prevention and rapid medical intervention.

Scombrotoxin: The Histamine Hazard

Scombrotoxin, also referred to as scombroid poisoning or histamine poisoning, occurs when fish containing high levels of histamine are consumed. This form of poisoning remains one of the most common worldwide, including in the United States.

Fish Species Prone to Scombrotoxin

Which fish are most likely to cause scombroid poisoning? High-risk species include:

Mahi mahi (dolphin fish)
Albacore tuna
Bluefin and yellowfin tuna
Bluefish
Mackerel
Sardines
Anchovy
Herring
Marlin
Amberjack
Abalone

These fish species naturally contain high levels of histidine, which can be converted to histamine under improper storage conditions.

Causes of Scombrotoxin Formation

How does scombrotoxin develop in fish? The primary cause is improper food handling, particularly:

Inadequate refrigeration
Prolonged storage at warm temperatures
Bacterial growth leading to histidine decarboxylation

Unlike other fish toxins, scombrotoxin is not naturally present in live fish but forms post-harvest due to mishandling.

Preventing Fish Poisoning: Safety Measures and Precautions

While fish neurotoxins pose significant health risks, there are several steps consumers can take to minimize their exposure and protect themselves from poisoning.

General Safety Guidelines

Be aware of high-risk fish species and their geographical distribution
Avoid consuming large predatory reef fish, especially in tropical areas
Purchase fish from reputable sources with proper handling practices
Ensure proper refrigeration of fish at all times
Cook fish thoroughly, although this does not destroy most neurotoxins

Specific Precautions for Different Toxins

How can you protect yourself from specific fish neurotoxins?

For ciguatera:

Avoid eating moray eel and barracuda
Be cautious with large reef fish from tropical waters
Consume smaller portions of potentially risky fish species

For tetrodotoxin:

Avoid consuming pufferfish unless prepared by licensed chefs
Be extremely cautious with fugu in Japan
Do not consume pufferfish caught recreationally

For scombrotoxin:

Ensure proper cooling of fish immediately after catch
Check for signs of spoilage before consumption
Avoid consuming fish with an unusually peppery or metallic taste

The Challenge of Detecting Fish Neurotoxins

One of the most challenging aspects of fish neurotoxins is their undetectable nature through conventional means. Why are these toxins so difficult to identify?

Invisibility to Sensory Detection

Fish containing neurotoxins do not exhibit any obvious signs of contamination. They do not look, smell, or taste different from uncontaminated fish. This makes it nearly impossible for consumers to identify toxic fish through sensory evaluation alone.

Resistance to Common Food Safety Practices

Traditional food safety methods are ineffective against fish neurotoxins. The toxins remain potent even after:

Cooking
Freezing
Marinating
Smoking
Drying

This resistance to common preparation methods further complicates prevention efforts.

Limitations of Testing Methods

While laboratory tests can detect the presence of fish neurotoxins, these are not practical for everyday consumer use. Current testing methods are:

Time-consuming
Expensive
Require specialized equipment
Not suitable for rapid, on-site testing

The lack of simple, accessible testing methods leaves consumers vulnerable to potential exposure.

Global Impact and Emerging Concerns

Fish neurotoxins are not just a localized issue but a global concern with far-reaching implications. How are these toxins affecting communities and ecosystems worldwide?

Economic Impact on Fishing Industries

The presence of neurotoxins in fish can have severe economic consequences for fishing communities and related industries:

Reduced consumer confidence in seafood products
Temporary or permanent fishing bans in affected areas
Increased costs for testing and monitoring
Loss of tourism in regions known for seafood cuisine

Climate Change and Toxin Distribution

How is climate change affecting the distribution of fish neurotoxins? Recent studies suggest that global warming may be expanding the range of toxic algal blooms, potentially leading to:

Increased incidence of ciguatera in previously unaffected areas
Changes in the geographical distribution of toxic fish species
Alterations in marine ecosystems that may favor toxin-producing organisms

Emerging Research and Future Directions

What are scientists doing to address the challenges posed by fish neurotoxins? Current research focus areas include:

Development of rapid, field-deployable testing methods
Investigation of potential antidotes or treatments for neurotoxin poisoning
Improved understanding of toxin production and accumulation in marine food chains
Exploration of sustainable fishing practices to minimize toxin exposure

These research efforts aim to enhance our ability to predict, prevent, and manage fish neurotoxin poisoning incidents in the future.

The Role of Education and Awareness

Combating the risks associated with fish neurotoxins requires a multi-faceted approach, with education and awareness playing crucial roles. How can increased knowledge help mitigate the dangers of these toxins?

Public Health Campaigns

Effective public health campaigns can significantly reduce the incidence of fish poisoning by:

Informing consumers about high-risk fish species and regions
Providing guidelines for safe fish consumption
Educating travelers about potential risks in tropical destinations
Promoting awareness of symptoms to encourage early medical intervention

Training for Healthcare Providers

Enhancing the knowledge of healthcare professionals is essential for prompt diagnosis and treatment. This includes:

Training in recognizing symptoms of different types of fish poisoning
Updating treatment protocols based on the latest research
Improving reporting mechanisms for poisoning incidents

Fisheries Management and Regulation

Implementing effective fisheries management practices can help reduce the risk of toxic fish entering the market:

Establishing monitoring programs for toxic algal blooms
Implementing seasonal or area-specific fishing restrictions
Enforcing strict handling and storage regulations for high-risk fish species
Developing traceability systems to track the origin of fish products

By combining these educational and regulatory efforts, it is possible to significantly reduce the global impact of fish neurotoxins and protect consumer health.

Fish Poisoning | Johns Hopkins Medicine

At certain times of the year, various species of fish and shellfish contain poisonous biotoxins, even if well cooked. According to the CDC, it is considered an under-recognized risk for travelers, specifically in the tropics and subtropics.

Certain fish—groupers, barracudas, moray eel, sturgeon, sea bass, red snapper, amberjack, mackerel, parrot fish, surgeonfish, and triggerfish—can cause ciguatera fish poisoning. The CDC recommends never eating moray eel or barracuda. Other types of fish that may contain the toxin at unpredictable times include sea bass and a wide range of tropical reef and warm-water fish. Fish containing these toxins do not look, smell, or taste bad. Cooking, marinating, freezing, or stewing does not destroy the toxin.

The risk of ciguatera poisoning exists in all tropical and subtropical waters of the West Indies, the Pacific Ocean, and the Indian Ocean, where these reef fish are eaten.

Two other forms of poisoning can happen from naturally occurring toxins in fish: tetrodotoxin, sometimes called pufferfish poisoning or fugu poisoning, and scombroid poisoning.

Where is the risk of ciguatera poisoning the greatest?

Reef fish from the tropical and subtropical waters of the West Indies, the Pacific Ocean, and the Indian Ocean pose the greatest threat. Cases have been reported in the United States in Hawaii, Guam, Puerto Rico, U.S. Virgin Islands, and Florida. A few isolated cases of ciguatera poisoning have even been noted along the eastern seaboard of the United States.

More than 400 species of fish, particularly reef fish, are thought to contain the toxin for ciguatera poisoning.

What are the symptoms of ciguatera poisoning?

Symptoms of ciguatera poisoning generally appear between a few minutes and 6 hours after the toxic fish has been eaten. These include a variety of gastrointestinal, neurological, and cardiovascular abnormalities. The following are the most common symptoms of ciguatera poisoning. However, each individual may experience symptoms differently. Symptoms may include:

In more severe cases, the person may suffer muscle pains, dizziness, and sensations of temperature reversal, where hot things seem cold and cold things seem hot. Irregular heart rhythms and low blood pressure may also be experienced. Ciguatera poisoning symptoms typically resolve within several days, but may last up to 4 weeks. The symptoms of ciguatera poisoning may resemble other medical conditions. Always talk with your healthcare provider for a diagnosis.

Treatment for ciguatera poisoning

Treatment for ciguatera poisoning involves relieving the symptoms and treating any complications. There is no specific antidote for the toxin itself. Generally, recovery takes from several days to several weeks.

What is tetrodotoxin?

Tetrodotoxin, also called pufferfish poisoning or fugu poisoning, is a much rarer form of fish poisoning. Yet, it is potentially very serious. This is almost exclusively associated with eating the pufferfish from waters of the Indo-Pacific regions. There have also been several reported cases of poisonings, including fatalities, from pufferfish from the Atlantic Ocean, Gulf of Mexico, and Gulf of California. Pufferfish poisoning is a continuing problem in Japan.

What are the symptoms of pufferfish poisoning?

Symptoms generally appear between 20 minutes and 3 hours after eating the poisonous pufferfish. The following are the most common symptoms of pufferfish poisoning. However, each individual may experience symptoms differently. Symptoms may include:

Numbness of lips and tongue
Numbness of face and extremities
Sensations of lightness or floating
Headache
Nausea and vomiting
Abdominal pain
Diarrhea
Slurred speech
Difficulty walking
Extensive muscle weakness
Convulsions
Respiratory distress
Mental impairment
Cardiac arrhythmia

Death can happen within 4 to 6 hours of poisoning. It is essential to seek immediate medical attention.

Treatment for pufferfish poisoning

Treatment for pufferfish poisoning consists of limiting the body’s absorption of the toxin, relieving symptoms, and treating life-threatening complications. There is no known antidote for tetrodotoxin.

What is scombrotoxin?

Scombrotoxin, also called scombroid poisoning or histamine poisoning, happens after eating fish that contain high levels of histamine due to improper food handling. It remains one of the most common forms of fish poisoning in the U.S. and worldwide. These fish, which include mahi mahi (dolphin fish), albacore tuna, bluefin and yellowfin tuna, bluefish, mackerel, sardines, anchovy, herring, marlin, amberjack, and abalone, have high amounts of histidine. As a result of inadequate refrigeration or preservation, bacteria convert the histidine to histamine. This leads to scombroid poisoning. Contaminated fish may appear and taste fresh, although some may taste “peppery,” “spicy,” or “bubbly. ” The toxin may form even if the fish has only been temporarily stored at too high a temperature.

This form of fish poisoning happens worldwide in temperate and tropical waters.

What are the symptoms of scombroid poisoning?

Symptoms generally appear within minutes to an hour after eating affected fish. They typically last 3 hours, but can last several days. The following are the most common symptoms of scombroid poisoning. However, each individual may experience symptoms differently. Symptoms may include:

Tingling or burning sensations in the mouth
Rash on the face and upper body
Wheezing or shortness of breath
Drop in blood pressure
Throbbing headache
Hives and itching of skin
Nausea
Vomiting
Diarrhea

The symptoms of scombroid poisoning may resemble other medical conditions. Many cases of “fish allergy” are actually scombroid poisoning. Always talk with your healthcare provider for a diagnosis.

Treatment for scombroid poisoning

Treatment for scombroid poisoning is generally unnecessary. Symptoms usually resolve within 12 hours and scombroid poisoning is rarely life-threatening. Treatment could include antihistamines, such as diphenhydramine and cimetidine.

Specific treatment for all fish and shellfish poisoning is based on:

Your overall health and medical history
Extent of the disease
Your tolerance for specific medicines, procedures, and therapies
Your opinion or preference

Neurotoxic Seafood Poisoning · California Poison Control System (CPCS)

Updated April, 2023 by Justin Seltzer, MD
Original author Jean Lo, MD

Introduction

Neurologic symptoms following consumption of seafood are uncommon but well described, with tens of thousands of cases annually worldwide and likely many more that are unreported and/or misdiagnosed. Neurotoxic seafood poisoning most often occurs following consumption of fish and shellfish. However, seafood consumption distant from where the animal was initially caught may complicate identification of the culprit organism. Further, diagnosis can be difficult, especially given limited provider familiarity with clinical syndromes.

Case 1 presentation

A 30 year old male was brought to the emergency department 6 hours after eating sea bass. His symptoms included perioral numbness and tingling, a strange metallic taste, and reversal of temperature discrimination. He was also mildly hypotensive and bradycardic.
Questions

What is the likely causative agent?
Where are the likely sources?
What is the physiologic mechanism by which the agent exerts its effects?

Case 2 presentation

A 25 year old female was brought to the emergency department 24 hours after eating specially prepared fish at a Japanese restaurant. Shortly after ingestion, she developed lip and tongue paresthesias. Four hours after ingestion, she became nauseated, vomited, and had abdominal pain. She presented with decreased strength in both of her legs.
Questions

What is the likely causative agent?
What are the likely sources?
What is the physiologic mechanism by which the agent exerts its effects?

Ciguatera poisoning

Ciguatera poisoning is the most common domestic vertebrate fishborne poisoning. It is associated with warm-water, bottom-dwelling shore reef fish from subtropical and tropical areas, including barracuda, sea bass, parrot fish, red snapper, grouper, amber jack, sturgeon, and kingfish. In the United States, Hawaii and Florida together account for approximately 90% of all domestic cases. However, cases have been reported in areas distant from the subtropical and tropical regions due to fish importation.

The etiology is thought to be due to toxins produced by photosynthetic dinoflagellates, namely Gambierdiscus toxicus, that contaminate the fish and cause clinical ciguatera toxicity when consumed by humans. No specific causative toxin has been identified and it is thought that clinical ciguatera toxicity may be due to several toxins. Ciguatoxin is the best characterized. Ciguatoxin binds to voltage-sensitive sodium channels in diverse tissues and increases the sodium permeability of the channel. These toxins are heat, cold, and acid stable and have no taste, smell, or color; no known method of preparation can eliminate the possibility of ciguatera.

Symptoms usually begin 2 to 6 hours after ingestion but can be significantly delayed by a day or longer. The clinical syndrome can produce a wide range of symptoms. Classically, ciguatera is associated with prodromal nausea, vomiting, and diarrhea followed by development of headaches, myalgias, paresthesias, numbness and tingling of the tongue, lips, throat, and perioral area, ataxia, vertigo, and hallucinations. Autonomic instability (hypo/hypertension, brady/tachycardia) can also occur and is usually rapid in onset. Some more peculiar neurologic findings associated with ciguatera include hot-cold reversal, cold allodynia, metallic taste, and a sensation of loose and/or painful teeth. Life threatening symptoms, such as dysrhythmias and seizures, have been reported but are rare. Most ciguatera symptoms resolve within a few days, though the neurotoxic effects can persist for weeks to months, or longer.

While ciguatera is not considered communicable between people under normal circumstances, transmission has been reported. Classically, sexual contact with an affected male can cause dyspareunia and other symptoms in a previously unaffected woman. There are scattered reports of babies becoming symptomatic after nursing from symptomatic mothers. Babies born to mothers with active ciguatera have also been reported to have been born with focal neurologic abnormalities that resolved within weeks, suggesting the possibility that ciguatera toxins can cross the placenta.

Management of acute ciguatera poisoning is mainly supportive with antiemetics, intravenous fluids, and chronotropic, circulatory support as needed. The neurologic abnormalities are difficult to treat and can be chronic. Some recommended treatments include gabapentin, pregabalin, amitriptyline and intravenous mannitol. Mannitol should only be used if the patient is appropriately volume resuscitated first to avoid further volume losses. Breastfeeding mothers should not breastfeed while actively symptomatic. A minority of patients may develop chronic neurologic and/or psychiatric manifestations, such as chronic fatigue.

One episode of ciguatera can cause sensitivity to ciguatera in the future, making it important to avoid reef fish for at least 6 months after the illness. Recurrent episodes are often more severe than the initial episode. Sensitivity, with recurrence of similar symptoms, has also been documented with consumption of alcohol, caffeine, and meats including other, unrelated fish as well as with exercise for months to years after.

Neurotoxic shellfish poisoning

Neurotoxic shellfish poisoning is a specific syndrome caused by ingestion of shellfish contaminated by brevetoxin. Common shellfish culprits include oysters, clams, mussels, and scallops.

Brevetoxin is released by the dinoflagellate Karenia brevis. Karenia brevis is best known for its role in toxic “red tides” along the Gulf coast. Although associated with the southwest Florida coast, brevetoxin has been reported throughout the entire US and Mexico Gulf coasts and the Atlantic coast north to North Carolina.

Brevetoxin binds to voltage-gated sodium channels and stimulates sodium flux through these channels. The resulting neurologic manifestations include paresthesias (classically starting circumoral then descending into the extremities), vertigo, ataxia, hyporeflexia, reversal of hot and cold temperature sensation, and seizures. Increased sodium influx also causes release of acetylcholine from postganglionic parasympathetic nerve endings, resulting in bronchospasm and bradycardia. Gastrointestinal symptoms, such as nausea, vomiting, diarrhea, and rectal burning can also occur and can appear simultaneously with the other symptoms. Symptom onset ranges between 15 minutes to 18 hours.

Management of neurotoxic shellfish poisoning is mainly supportive. Respiratory symptoms can usually be managed with beta agonists such as albuterol and antimuscarinic bronchodilators.

Paralytic shellfish poisoning

Paralytic shellfish poisoning occurs following ingestion of saxitoxin contaminated shellfish, mainly bivalve mollusks (e.g, clams, oysters, mussels, and scallops). Poisoning has also occurred through consumption of other aquatic animals, such as sand crabs, reef crabs, and purple starfish. Saxitoxin-contaminated shellfish generally originate from the Pacific Northwest and Northeast Atlantic coast. The common season for this poisoning is between May and November.

Saxitoxins compounds are a large group of related toxins produced by a variety of dinoflagellates. Saxitoxin is the best characterized of the toxins. The other saxitoxins compounds are structurally derived from saxitoxin, varying by different R groups.

Saxitoxin acts through blockade of the voltage-sensitive sodium channels, thus blocking propagation of nerve and skeletal muscle action potentials. Symptoms usually occur within 30 minutes of ingestion. Neurologic symptoms predominate and include paresthesias, headache, ataxia, cranial nerve dysfunction, muscle weakness and paralysis. Gastrointestinal symptoms such as nausea, vomiting, diarrhea, and abdominal pain can occur but are less common.
Mortality is reported to be 2.6 to 23.2% in a series of paralytic shellfish poisoning and is most often secondary to respiratory failure. Toxicity peaks at around 12 hours after symptom onset, and the prognosis is good if the patient survives the first 12 hours. However, muscle weakness may persist for weeks. Management is supportive care with early intervention for neuromuscular weakness and respiratory failure.

Tetrodotoxin

Tetrodotoxin is a neurotoxin famously present in the Japanese puffer fish (fugu) and blue-ring octopus. Other sources include puffer-like fish (e.g. globe fish, balloon fish, blowfish, and toad fish), gastropod mollusks (e.g. lined moon shell, frog shell), horseshoe crab eggs, and some starfish, flatworms, and newt species.
Fugu is considered a seafood delicacy in Japan, with the tetrodotoxin effects considered an important element. The flavor of fugu is considered to be at its best from November to February, which are the months when the toxin content of the ovaries and liver in these fish increases. Tetrodotoxin-containing puffer fish is still served by certified chefs and coveted for its mild neurotoxic properties when eaten. Fugu imported to the United States is required to be tetrodotoxin-free via a complex certification process.

Tetrodotoxin is one of the most lethal toxins known and acts via inhibition of sodium channels and blocking propagation of nerve and skeletal muscle action potentials. It is heat stable.

Symptoms usually occur within minutes of ingestion and initially include headache, diaphoresis, and dysesthesias and paresthesias of the lips, tongue, mouth, face, fingers, and toes. Neuromuscular dysfunction manifesting as dysphagia, dysarthria, loss of coordination, fasciculations, and ascending paralysis with neuromuscular respiratory weakness with preserved consciousness can develop in a delayed fashion, usually 4 to 24 hours after ingestion. Hemodynamic instability can occur as well.
Management is supportive care with early airway protection and hemodynamic support as needed. Mortality in some series has been reported up to 50%. However, with aggressive supportive care including early ventilatory and hemodynamic support, the prognosis is better.

Amnesic shellfish poisoning

Amnesic shellfish poisoning is caused by domoic acid, a structural analog of glutamic and kainic acids. Domoic acid is produced by certain phytoplankton found along the Pacific Coast of North America, eastern Canadian Atlantic coast, and Gulf of Mexico, which are thought to be responsible for several historic outbreaks in these areas. Organisms that feed on domoic acid producing phytoplankton, such as shellfish, sardines, and anchovies, then become contaminated with domoic acid and cause toxicity when consumed. Domoic acid is heat stable.

Domoic acid causes excitatory neurotoxicity, leading to neuronal loss primarily within the thalamus, forebrain, and hippocampus. Hippocampal involvement is what is thought to mediate the memory loss and disorientation.

Symptoms usually begin within minutes but can take more than a day to develop after ingestion of contaminated shellfish. Gastrointestinal symptoms, such as nausea, vomiting, and diarrhea, typically precede neurological symptoms, and most often occur within 24 hours, while neurological symptoms usually occur after 48 hours. Neurological symptoms include memory loss, disorientation, ophthalmoplegia, hyporeflexia, skeletal muscle weakness, abnormal movements such as purposeless chewing and grimacing, seizures, and depressed level of consciousness. Cardiac dysrhythmias and hemodynamic instability can develop.

Management is largely supportive, with benzodiazepines for seizures if needed.

Mortality is low and usually occurs in older patients. However, affected patients are at risk for long-term anterograde memory deficits and motor and sensory neuropathy following resolution of the acute toxicity.

Palytoxins

Palytoxins are among one of the most dangerous marine toxins known. Palytoxins have been associated with some severe cases of ciguatera and is the toxin thought to cause a clinical syndrome known as “clupeotoxism” following consumption of Clupeidae such as sardines, herrings, and anchovies. It is mostly seen in subtropical and subtropical regions and can contaminate and bioaccumulate in any organism that lives in proximity to or feeds on palytoxin producing corals or dinoflagellates. Consumption of these contaminated organisms leads to human toxicity. Palytoxin exposure can also occur from handling of Palythoa corals, aerosolized toxins emanating from dinoflagellate blooms, and from cleaning aquarium tanks containing these organisms. Palytoxin is heat stable.

Palytoxin, the best described of the group of palytoxins, is thought to cause toxicity by a unique effect on the sodium-potassium ATPase in which the transporter is stuck in the open conformation, allowing sodium and potassium to passively diffuse across the cell membranes via the open transporter; effectively, palytoxin turns the sodium-potassium ATPase from an active transporter to an open ion channel. This destroys the ion gradient necessary for cellular sodium and potassium homeostasis. Ultimately, this leads to widespread cellular dysfunction and damage.

Signs and symptoms of palytoxin poisoning are not well defined due to the rarity of exposure and diversity of exposure types and routes. Toxicity from ingestion has been noted to cause nausea, vomiting, diarrhea, abdominal pain, and metallic taste rapidly followed by development of severe headache, anxiety, myalgias, dyspnea, vertigo, paresthesias, muscular weakness, seizures, and depressed level of consciousness leading to coma. Signs of shock, such as tachycardia, hypotension, and cool skin and extremities, have also been reported. Death can occur rapidly, reportedly within minutes. Those not experiencing rapid onset life threatening symptoms have shown evidence of widespread cellular damage, manifesting clinically as hemolysis and rhabdomyolysis. Similar marine syndromes primarily resulting in rhabdomyolysis, such as Haff disease, are thought to be related to palytoxin or palytoxin-like exposure as well, though no conclusive evidence of this has yet been shown.

Toxicity from other exposure routes, such as aerosol or skin/mucus membrane exposure, are even more poorly defined. Aerosols are thought to cause local irritant symptoms such as cough, dyspnea, wheezing, fever, and conjunctivitis. Skin exposure can result in local edema and erythema along with milder systemic symptoms such as perioral paresthesias and myalgias; ocular exposure can cause pain, conjunctival injection, and vision impairment with reports of resulting severe corneal injury. Significant exposures may be associated with long term neurologic symptoms and neurocognitive impairment. Management is supportive.

Case 1

Question Answers

What is the likely causative agent? Ciguatoxin. The ingestion of sea bass, reversal of temperature discrimination, hypotension and bradycardia are predominant clues.
Where are the likely sources? Ciguatoxin originates from photosynthetic dinoflagellates like Gambierdiscus toxicus, and bacteria within the dinoflagellates. Dinoflagellates are the main food source for small fish, leading eventually to bioconcentration into larger predator fish such as barracuda, sea bass, parrot fish, red snapper, grouper, amber jack, sturgeon, and kingfish. Ciguatoxin can be found in higher concentrations in the flesh, adipose tissue, and viscera of these larger fish.
What is the physiologic mechanism by which ciguatoxin exerts its effects? Ciguatoxin binds to voltage-sensitive sodium channels in diverse tissues and increases the sodium permeability of the channel.

Case 2

Question Answers

What is the likely causative agent? Tetrodotoxin. The lip and tongue paresthesias, subsequent gastrointestinal symptoms, and finally ascending paralysis are characteristic.
Where are the likely sources? Tetrodotoxin is found in fugu, a Japanese puffer fish consumed as a delicacy in Japan. Tetrodotoxin can also be found in puffer-like fish, gastropod mollusks, the blue-ring octopus, horseshoe crab eggs, starfish, flatworms, and some newts.
What is the physiologic mechanism by which tetrodotoxin exerts its effects? Tetrodotoxin acts via inhibition of sodium channels and blocking propagation of nerve and skeletal muscle action potentials.

Fish poison is out of control

May 18, 2012, 17:58
Society

Thrill-seekers will be able to risk their lives in Tokyo restaurants as the city authorities intend to lift strict restrictions on the preparation of puffer fish, which contains high concentrations of the poison tetrodotoxin. When it enters the digestive tract, the poison causes severe pain, convulsions, and then paralysis and death due to respiratory arrest. However, there is a tradition in the country: if a visitor gets poisoned by fugu, then the cook must finish the dish.

For more than fifty years, the rule in Japan has been that in order to cook fugu, chefs must work for two years as assistants to experienced masters, and then pass a written and practical exam, paying $ 220 for it. Such cooks can correctly remove the poisonous skin from the fish, carefully remove the poisoned innards, and properly process the meat so that the remaining poison does not kill the client, but causes a feeling of slight paralysis – a narcotic effect for which diners order a dangerous dish. Tokyo City Hall has now announced that anyone can work with fugu, provided that the restaurant buys already butchered carcasses, reports BBC . It is planned that the innovation will come into effect this fall.

Previously, such proposals aroused indignation both among chefs who do not want to lose their reputation, and restaurant visitors, for whom ordering fugu is tantamount to playing Russian roulette. About 40 people are known to have been poisoned in Tokyo between 1996 and 2006. True, only one of them ate a dish in a restaurant. The rest were fishermen and ate the fish from their catch. The last case of poisoning occurred in a Tokyo restaurant in November 2011, when a woman forced the chef to cook fugu liver for her. The 35-year-old visitor knew that the liver had the most poison. As a result, the doctors had to fight for her life, and the cook lost his job.

Puffer fish is the name given to several species of fish from the pufferfish family. Most often, brown puffer or dog fish are used to prepare the dish. The body of the fish does not produce neurotoxin, it is produced by bacteria that are eaten by a variety of marine life that serves as food for pufferfish. To reduce the concentration of poison in fish, the Japanese catch fry and then feed them in special cages.

The navigator James Cook, who was fed fugu by the natives, described his sensations: “About three or four o’clock in the morning we felt an unprecedented weakness in all the members, accompanied by such a sensation as if the hands and feet, stiff in the cold, had immediately fallen into the fire. I almost felt nothing and even lost the ability to measure the heaviness of bodies: a mug of water and a pen seemed equally heavy in my hand.

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