Fish neurotoxin. Ciguatera Fish Poisoning: Understanding Risks, Symptoms, and Treatment

29.08.202319.07.2023 by alexxlab

What are the symptoms of ciguatera poisoning. How can you identify potentially toxic fish. What areas pose the highest risk for ciguatera poisoning. How is ciguatera poisoning treated. What other types of fish poisoning exist. How do symptoms differ between various fish toxins. Where can travelers find reliable information on fish poisoning risks.

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The Hidden Dangers of Ciguatera Fish Poisoning

Ciguatera fish poisoning is a form of foodborne illness caused by consuming certain reef fish that have accumulated ciguatoxins through their diet. These potent neurotoxins originate from dinoflagellates, microscopic algae that live on coral reefs. As smaller fish consume these algae, the toxins move up the food chain, becoming more concentrated in larger predatory fish.

Despite being a significant health concern, particularly in tropical and subtropical regions, ciguatera poisoning often goes underreported and underrecognized. This is partly due to the difficulty in diagnosing the condition and the fact that the toxins responsible cannot be destroyed by normal cooking methods.

High-Risk Fish Species

While over 400 species of fish have been associated with ciguatera poisoning, some are more frequently implicated than others. These include:

Groupers
Barracudas
Moray eels
Snappers
Jacks
Mackerel
Parrotfish
Surgeonfish
Triggerfish

It’s important to note that the presence of ciguatoxins in these fish is unpredictable and cannot be detected by smell, taste, or appearance. This makes it challenging for consumers to identify potentially dangerous fish.

Geographical Distribution of Ciguatera Risk

Ciguatera poisoning is primarily associated with reef ecosystems in tropical and subtropical waters. The regions with the highest risk include:

The Caribbean Sea
The Pacific Ocean, particularly around Hawaii and other Pacific islands
The Indian Ocean

In the United States, cases have been reported in Hawaii, Guam, Puerto Rico, the U.S. Virgin Islands, and Florida. Interestingly, there have been isolated incidents along the eastern seaboard of the United States, highlighting the potential for the toxin to affect areas outside its typical range.

Is ciguatera poisoning becoming more widespread?

There is growing concern that climate change and increasing sea surface temperatures may be expanding the geographical range of the dinoflagellates responsible for producing ciguatoxins. This could potentially lead to ciguatera poisoning becoming a problem in previously unaffected areas. Researchers are actively monitoring this situation to better understand the potential future impacts on global fish safety.

Recognizing the Symptoms of Ciguatera Poisoning

The symptoms of ciguatera poisoning can vary in severity and typically appear within a few minutes to 6 hours after consuming contaminated fish. The diverse range of symptoms can be categorized into three main groups:

Gastrointestinal Symptoms

Nausea
Vomiting
Diarrhea
Abdominal pain

Neurological Symptoms

Tingling and numbness in extremities
Itching
Blurred vision
Tooth pain or feeling as if teeth are loose
Temperature reversal (cold objects feeling hot and vice versa)

Cardiovascular Symptoms

Irregular heartbeat
Low blood pressure
Bradycardia (slow heart rate)

In severe cases, individuals may experience muscle pains, dizziness, and hallucinations. While most symptoms resolve within several days to weeks, some neurological effects can persist for months or even years in rare cases.

Diagnosis and Treatment of Ciguatera Poisoning

Diagnosing ciguatera poisoning can be challenging due to the similarity of its symptoms to other foodborne illnesses. Currently, there is no widely available test to confirm the presence of ciguatoxins in human specimens. Diagnosis is typically based on a combination of clinical symptoms and recent dietary history.

How is ciguatera poisoning treated?

Treatment for ciguatera poisoning is primarily supportive, focusing on managing symptoms and preventing complications. There is no specific antidote for the toxin. The main components of treatment include:

Intravenous fluids to prevent dehydration
Medications to control nausea and vomiting
Pain relievers for headaches and muscle pain
Antihistamines to reduce itching
In some cases, mannitol may be administered to help alleviate neurological symptoms

Most people recover from ciguatera poisoning within days to weeks, but in some cases, symptoms can persist for months or even years. Individuals who have experienced ciguatera poisoning may be more sensitive to future exposures and should be cautious about consuming reef fish from high-risk areas.

Preventing Ciguatera Fish Poisoning

Given that ciguatoxins cannot be destroyed by cooking, freezing, or other food preparation methods, prevention primarily relies on avoiding consumption of high-risk fish species from areas known to have ciguatera.

Tips for reducing the risk of ciguatera poisoning:

Avoid eating large predatory reef fish, especially those weighing more than 6 pounds
Be cautious when consuming fish caught in tropical or subtropical waters
Seek local knowledge about which fish species are considered safe to eat in a particular area
When traveling, consider choosing smaller, herbivorous fish species which are less likely to accumulate high levels of toxins
Be aware that ciguatoxins are tasteless and odorless, so sensory inspection cannot determine if a fish is safe

It’s important to note that commercial fishing operations and regulatory bodies in many countries have implemented measures to reduce the risk of ciguatoxic fish entering the market. However, the risk can never be completely eliminated, especially for locally caught fish in endemic areas.

Other Types of Fish Poisoning: Tetrodotoxin and Scombrotoxin

While ciguatera is a significant concern, it’s not the only type of fish poisoning that can affect humans. Two other notable forms are tetrodotoxin poisoning and scombrotoxin poisoning.

Tetrodotoxin (Pufferfish) Poisoning

Tetrodotoxin poisoning, 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 (fugu) from Indo-Pacific waters, although cases have been reported from pufferfish in the Atlantic Ocean, Gulf of Mexico, and Gulf of California.

Symptoms of tetrodotoxin poisoning typically appear between 20 minutes and 3 hours after ingestion and can include:

Numbness of lips, tongue, face, and extremities
Sensations of lightness or floating
Headache and nausea
Difficulty walking and speaking
Muscle weakness and paralysis
Respiratory distress
Cardiac arrhythmia

Tetrodotoxin poisoning can be life-threatening, with death occurring within 4 to 6 hours in severe cases. There is no specific antidote, and treatment focuses on supportive care and managing complications.

Scombrotoxin (Histamine) Poisoning

Scombrotoxin poisoning, also called scombroid poisoning or histamine poisoning, is one of the most common forms of fish poisoning worldwide. It occurs when fish containing high levels of histidine are improperly handled or stored, allowing bacteria to convert the histidine to histamine.

Fish commonly associated with scombrotoxin poisoning include:

Tuna (albacore, bluefin, yellowfin)
Mahi-mahi
Mackerel
Sardines
Anchovies
Marlin
Bluefish

Symptoms of scombrotoxin poisoning typically appear rapidly, within minutes to a few hours after consuming contaminated fish, and can include:

Flushing of the face and neck
Headache
Heart palpitations
Itching
Blurred vision
Cramps and diarrhea

While scombrotoxin poisoning is generally less severe than ciguatera or tetrodotoxin poisoning, it can still cause significant discomfort and, in rare cases, more serious complications.

The Impact of Fish Poisoning on Global Health and Economy

Fish poisoning, particularly ciguatera, has far-reaching implications beyond individual health concerns. It affects local and global economies, influences fishing practices, and poses challenges for food security in many regions.

Economic Impact

The economic consequences of fish poisoning are multifaceted:

Reduced fish consumption in affected areas, impacting local fishing industries
Increased healthcare costs associated with treating poisoning cases
Loss of productivity due to illness
Negative effects on tourism in regions known for seafood cuisine

In some Pacific island nations, where fish is a primary source of protein, the fear of ciguatera poisoning has led to changes in dietary habits, potentially affecting nutrition and food security.

Challenges for the Fishing Industry

The fishing industry faces several challenges related to fish poisoning:

Implementing effective testing methods to identify contaminated fish
Developing strategies to fish in areas with lower risk of ciguatoxin contamination
Educating fishers and consumers about the risks and safe practices
Adapting to potential shifts in fish populations due to climate change

These challenges require collaboration between the fishing industry, scientists, and regulatory bodies to ensure the safety of fish products while maintaining sustainable fishing practices.

Research and Future Directions in Fish Poisoning Prevention

Ongoing research in the field of fish poisoning is focused on several key areas:

Improved Detection Methods

Scientists are working on developing more accurate and accessible methods for detecting ciguatoxins and other marine toxins in fish. These include:

Rapid test kits that can be used in the field
Advanced laboratory techniques for quantifying toxin levels
Biomarkers that could indicate previous exposure to ciguatoxins in humans

Understanding Toxin Production and Accumulation

Research is ongoing to better understand the environmental factors that influence the production of ciguatoxins by dinoflagellates and their accumulation in the food chain. This knowledge could help predict high-risk areas and seasons.

Potential Treatments

While current treatment for ciguatera poisoning is primarily supportive, researchers are exploring potential therapies that could directly target the toxins or their effects on the body. Some areas of investigation include:

Compounds that could bind to and neutralize ciguatoxins
Medications that could block the effects of ciguatoxins on nerve cells
Therapies to address the long-term neurological symptoms some patients experience

Climate Change and Fish Poisoning

As global temperatures rise, there is increasing concern about how climate change might affect the distribution and prevalence of fish poisoning. Research is being conducted to:

Model the potential spread of ciguatoxin-producing organisms to new areas
Understand how changes in ocean chemistry might affect toxin production
Predict how shifts in fish populations could alter the risk of various types of fish poisoning

This research is crucial for developing proactive strategies to mitigate the potential increased risk of fish poisoning in a changing climate.

Global Efforts to Combat Fish Poisoning

Addressing the challenge of fish poisoning requires coordinated efforts on a global scale. Various international organizations, governments, and research institutions are working together to improve understanding, prevention, and management of fish poisoning.

World Health Organization (WHO) Initiatives

The WHO has recognized ciguatera fish poisoning as an important food safety issue. Their efforts include:

Providing guidance on risk assessment and management
Supporting research into improved detection methods
Facilitating information sharing between affected countries

Regional Cooperation

In areas where fish poisoning is prevalent, regional cooperation is crucial. Examples include:

The Pacific Ciguatera Fish Poisoning Project, which involves collaboration between Pacific Island nations
The Caribbean Ciguatera Strategy, aimed at improving management and communication about ciguatera risks in the region

Education and Awareness Programs

Many countries and organizations are implementing education programs to raise awareness about fish poisoning. These programs often target:

Local communities in high-risk areas
Tourists and travelers
Healthcare providers to improve diagnosis and reporting
Fishers and fish vendors to promote safe practices

By combining research, policy, and education efforts, the global community aims to reduce the incidence of fish poisoning and mitigate its impacts on health and economies worldwide.

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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