Toxigenic Algae And Algal Food Poisoning- An Overview

Algae are photosynthetic organisms that live in aquatic environments and produce oxygen and organic matter. However, some algae can also produce harmful substances called toxins that can affect the health of humans and animals. These toxins can cause various types of food poisoning when ingested through contaminated seafood or water. In this article, we will introduce three major groups of toxin-producing algae: dinoflagellates, diatoms and cyanobacteria.

Dinoflagellates are microscopic, single-celled algae that have two flagella for movement. They are found in both freshwater and marine ecosystems, and some of them can form large blooms that change the color of the water. These blooms are sometimes called red tides or harmful algal blooms (HABs). Dinoflagellates can produce different types of toxins that affect the nervous system, the digestive system or the blood cells of animals and humans. Some examples of these toxins are:

• Ciguatoxins: These are lipid-soluble toxins that accumulate in the flesh of large reef fish such as barracuda, grouper and snapper. They cause ciguatera fish poisoning, which is characterized by gastrointestinal symptoms (nausea, vomiting, diarrhea), neurological symptoms (numbness, tingling, pain, weakness) and cardiovascular symptoms (low blood pressure, irregular heartbeat). Ciguatoxins can also be transmitted through sexual contact or breast milk and affect the fetus or the newborn.
• Saxitoxins: These are water-soluble toxins that bind to sodium channels and block nerve impulses. They cause paralytic shellfish poisoning (PSP), which is characterized by tingling, numbness, drowsiness, respiratory paralysis and death. Saxitoxins are found in shellfish such as clams, mussels, oysters and scallops that feed on toxic dinoflagellates. They can also be found in some fish such as pufferfish and needlefish.
• Brevetoxins: These are lipid-soluble toxins that activate sodium channels and cause nerve depolarization. They cause neurotoxic shellfish poisoning (NSP), which is characterized by gastrointestinal symptoms (nausea, vomiting, diarrhea), neurological symptoms (tingling, numbness, headache, dizziness) and respiratory symptoms (coughing, wheezing, difficulty breathing). Brevetoxins are found in shellfish that feed on toxic dinoflagellates such as Karenia brevis. They can also become airborne and cause respiratory irritation to people living near the coast.

Diatoms are microscopic algae that have a cell wall made of silica. They are found in both freshwater and marine ecosystems, and they form the base of many food webs. Diatoms can produce different types of toxins that affect the liver, the kidneys or the nervous system of animals and humans. Some examples of these toxins are:

• Domoic acid: This is a water-soluble toxin that mimics glutamate and activates excitatory receptors in the brain. It causes amnesic shellfish poisoning (ASP), which is characterized by gastrointestinal symptoms (nausea, vomiting, diarrhea), neurological symptoms (confusion, memory loss, seizures) and death. Domoic acid is found in shellfish that feed on toxic diatoms such as Pseudo-nitzschia spp. It can also affect marine mammals such as sea lions and dolphins that eat contaminated fish.
• Okadaic acid: This is a lipid-soluble toxin that inhibits protein phosphatases and disrupts cellular functions. It causes diarrhetic shellfish poisoning (DSP), which is characterized by gastrointestinal symptoms (nausea, vomiting, diarrhea) and dehydration. Okadaic acid is found in shellfish that feed on toxic diatoms such as Dinophysis spp. It can also affect fish such as sardines and anchovies that eat contaminated plankton.
• Palytoxin: This is a lipid-soluble toxin that binds to sodium-potassium pumps and causes massive ion fluxes across cell membranes. It causes palytoxin poisoning, which is characterized by gastrointestinal symptoms (nausea, vomiting, diarrhea), cardiovascular symptoms (low blood pressure, irregular heartbeat) and respiratory symptoms (difficulty breathing). Palytoxin is found in some corals such as Palythoa spp. It can also be released into the air when these corals are disturbed or handled.

Cyanobacteria are bacteria that perform photosynthesis and produce oxygen. They are also known as blue-green algae and they are found in both freshwater and marine ecosystems. Cyanobacteria can produce different types of toxins that affect the liver, the kidneys, the nervous system or the skin of animals and humans. Some examples of these toxins are:

• Microcystins: These are cyclic peptides that inhibit protein phosphatases and cause liver damage. They cause hepatotoxic cyanobacterial poisoning, which is characterized by gastrointestinal symptoms (nausea, vomiting, diarrhea), liver symptoms (jaundice, bleeding, failure) and death. Microcystins are found in freshwater cyanobacteria such as Microcystis spp. They can also affect livestock and pets that drink contaminated water.
• Nodularins: These are cyclic peptides that inhibit protein phosphatases and cause liver damage. They cause nodularin poisoning, which is characterized by gastrointestinal symptoms (nausea, vomiting, diarrhea), liver symptoms (jaundice, bleeding, failure) and death. Nodularins are found in brackish water cyanobacteria such as Nodularia spumigena. They can also affect fish and shellfish that feed on toxic cyanobacteria.
• Anatoxins: These are alkaloids that mimic acetylcholine and activate nicotinic receptors in the nervous system. They cause anatoxin poisoning, which is characterized by neurological symptoms (tremors, convulsions, paralysis) and death. Anatoxins are found in freshwater cyanobacteria such as Anabaena spp. They can also affect livestock and pets that drink contaminated water or eat contaminated plants.
• Cylindrospermopsins: These are alkaloids that inhibit protein synthesis and cause liver and kidney damage. They cause cylindrospermopsin poisoning, which is characterized by gastrointestinal symptoms (nausea, vomiting, diarrhea), liver symptoms (jaundice, bleeding, failure) and kidney symptoms (blood in urine, failure). Cylindrospermopsins are found in freshwater cyanobacteria such as Cylindrospermopsis spp. They can also affect livestock and pets that drink contaminated water or eat contaminated plants.

These are some of the main toxins produced by algae and their effects on humans and animals. In the next sections, we will discuss the route of exposure to algal food poisoning, the toxicokinetics of algal toxins, the effects of acute and chronic toxicity, and the control and clinical management of algal food poisoning.

Algal food poisoning can occur when humans or animals ingest or inhale toxins produced by certain algae species. The most common route of exposure is through the consumption of contaminated seafood products such as shellfish, fish, and crustaceans. Some of the algal toxins that can cause food poisoning are:

• Ciguatoxins and maitotoxins, which are produced by dinoflagellates that grow on coral reefs and accumulate in large reef fish such as barracuda, grouper, snapper, and amberjack. These toxins cause ciguatera poisoning, which is characterized by gastrointestinal, neurological, and cardiovascular symptoms. Ciguatoxins and maitotoxins can also be transmitted through sexual contact and affect the fetus and newborn babies.
• Saxitoxins, which are produced by dinoflagellates that cause red tides or harmful algal blooms in marine and freshwater environments. These toxins accumulate in filter-feeding shellfish such as clams, mussels, scallops, and oysters, and cause paralytic shellfish poisoning (PSP), which is characterized by numbness, tingling, weakness, and respiratory paralysis. Saxitoxins can also be found in some fish species such as pufferfish, which can cause tetrodotoxin poisoning or fugu poisoning.
• Domoic acid, which is produced by diatoms that cause harmful algal blooms in coastal waters. This toxin accumulates in shellfish such as mussels, clams, scallops, and oysters, and fish such as anchovies, sardines, and herring. Domoic acid causes amnesic shellfish poisoning (ASP), which is characterized by gastrointestinal symptoms, memory loss, confusion, seizures, and coma.
• Brevetoxins, which are produced by dinoflagellates that cause red tides or harmful algal blooms in warm coastal waters. These toxins affect the nervous system of fish and marine mammals, causing them to die or become disoriented. Brevetoxins can also become airborne when the algae cells are broken by waves or wind, and cause respiratory irritation to humans who inhale them. Brevetoxins cause neurotoxic shellfish poisoning (NSP), which is characterized by gastrointestinal symptoms, tingling sensations, dizziness, and muscle weakness.
• Microcystins, anatoxins, cylindrospermopsins, and other toxins produced by cyanobacteria or blue-green algae that grow in freshwater lakes, ponds, reservoirs, and rivers. These toxins can affect the liver, kidney, nervous system, skin, and other organs of humans and animals who drink or swim in contaminated water. Microcystins cause hepatotoxicity or liver damage; anatoxins cause neurotoxicity or nerve damage; cylindrospermopsins cause cytotoxicity or cell damage.

The risk of algal food poisoning depends on several factors such as the type and amount of toxin ingested or inhaled; the age, weight, health status, and genetic susceptibility of the person or animal exposed; the presence of other contaminants or pathogens in the food or water; and the availability of medical treatment. Algal food poisoning can be prevented by avoiding consumption of seafood from areas affected by harmful algal blooms; monitoring the water quality and algal toxin levels; cooking seafood thoroughly; wearing protective masks when near red tide areas; and seeking medical attention if symptoms occur.

Toxicokinetics is the study of how toxins are absorbed, distributed, metabolized and excreted by the body. Different algal toxins have different toxicokinetic properties that affect their toxicity and health effects.

Absorption

Algal toxins can enter the body through various routes such as ingestion, inhalation, skin contact or sexual contact. The most common route of exposure is through the consumption of contaminated seafood products such as shellfish or fish. The absorption of algal toxins depends on their chemical structure, solubility and stability. Lipophilic toxins such as ciguatoxins and brevetoxins are easily absorbed from the gastrointestinal tract and can cross the blood-brain barrier. Hydrophilic toxins such as saxitoxins and domoic acid are less readily absorbed and have limited access to the central nervous system.

Distribution

Once absorbed, algal toxins are distributed throughout the body via the bloodstream. The distribution of algal toxins depends on their affinity for different tissues and organs. Some algal toxins have a high affinity for specific organs such as the liver (microcystins), the brain (anatoxins) or the heart (maitotoxins). Other algal toxins have a more widespread distribution such as brevetoxins and domoic acid. The distribution of algal toxins can also be influenced by factors such as age, gender, pregnancy, lactation and nutritional status.

Metabolism

Metabolism is the process of transforming algal toxins into less toxic or more water-soluble forms that can be eliminated from the body. The metabolism of algal toxins occurs mainly in the liver, but also in other organs such as the kidneys, lungs and intestines. The metabolism of algal toxins involves various enzymatic reactions such as oxidation, reduction, hydrolysis, conjugation and glucuronidation. The metabolism of algal toxins can vary depending on the species, dose and duration of exposure. Some algal toxins are metabolized rapidly and completely such as saxitoxins and domoic acid. Other algal toxins are metabolized slowly and incompletely such as ciguatoxins and microcystins.

Excretion

Excretion is the process of eliminating algal toxins from the body. The excretion of algal toxins occurs mainly through urine and feces, but also through sweat, saliva, bile and milk. The excretion of algal toxins depends on their chemical structure, solubility and stability. Water-soluble toxins such as saxitoxins and domoic acid are excreted quickly and efficiently. Lipid-soluble toxins such as ciguatoxins and brevetoxins are excreted slowly and incompletely. Some algal toxins can be reabsorbed from the intestines or recycled in the enterohepatic circulation such as microcystins and anatoxins.

The toxicokinetics of algal toxins determines their bioavailability, bioaccumulation and biomagnification in the food chain. The toxicokinetics of algal toxins also influences their clinical manifestations, diagnosis and treatment. Understanding the toxicokinetics of algal toxins is essential for assessing their risk to human health and developing effective prevention and management strategies.

The effects of algal toxins on humans and animals depend on the type, dose, and duration of exposure. Algal toxins can cause acute or chronic toxicity, which have different symptoms and health consequences.

Acute toxicity refers to the adverse effects that occur within a short time (usually hours or days) after a single or multiple exposures to a high dose of a toxin. Acute toxicity can result in severe symptoms such as nausea, vomiting, diarrhea, abdominal pain, headache, dizziness, muscle weakness, respiratory distress, cardiac arrhythmia, seizures, coma, and death.

Chronic toxicity refers to the adverse effects that occur after repeated or prolonged exposures to a low dose of a toxin over a long time (usually months or years). Chronic toxicity can result in subtle or delayed symptoms such as liver damage, kidney damage, neurodegeneration, cancer, reproductive impairment, immune suppression, and endocrine disruption.

The acute and chronic toxicity of algal toxins can vary depending on the species of algae, the environmental conditions, the route of exposure, and the susceptibility of the exposed organism. Some algal toxins are more potent than others and some organisms are more sensitive than others. For example, saxitoxin is one of the most toxic algal toxins known and can cause paralysis and death in humans and animals within minutes after ingestion. On the other hand, microcystin is a less toxic algal toxin but can cause chronic liver damage and cancer after long-term exposure.

The effects of acute and chronic toxicity of algal toxins can also be influenced by interactions with other chemicals or stressors in the environment. For example, some algal toxins can enhance the toxicity of pesticides or metals by increasing their bioavailability or disrupting their metabolism. Some algal toxins can also increase the susceptibility of organisms to infections or diseases by impairing their immune system.

Therefore, it is important to monitor and manage the occurrence and exposure of algal toxins in water resources to protect human and animal health from acute and chronic toxicity.

The prevention and control of algal food poisoning depend on the monitoring and surveillance of algal blooms and seafood contamination. The following measures can help to reduce the risk of exposure and illness:

• Avoid eating raw or undercooked shellfish, especially during algal bloom seasons or in areas with known contamination.
• Check for advisories or warnings before harvesting or consuming shellfish from coastal waters.
• Discard any shellfish that have an unusual odor, color, or texture.
• Wash and cook shellfish thoroughly before eating. Cooking can destroy some toxins, but not all. Boiling or steaming is preferable to frying or baking, as some toxins can become more concentrated in the oil or fat.
• Do not eat the viscera (guts) of shellfish, as they may contain higher levels of toxins than the flesh.
• Avoid contact with algal blooms in freshwater or marine environments. Wear protective clothing and gloves if handling algae or contaminated water. Rinse off with clean water after exposure.
• Do not drink water from sources that may be affected by algal blooms. Use bottled water or treat water with filtration, boiling, or disinfection methods.
• Seek medical attention immediately if you experience any symptoms of algal food poisoning, such as nausea, vomiting, diarrhea, abdominal pain, tingling, numbness, dizziness, headache, or difficulty breathing. Inform your doctor about your recent seafood consumption and possible exposure to algal blooms.

The treatment of algal food poisoning is mainly supportive and symptomatic. There is no specific antidote for most algal toxins. The following interventions can help to manage the condition:

• Gastric lavage or activated charcoal may be administered to reduce the absorption of toxins from the gastrointestinal tract. This should be done as soon as possible after ingestion, preferably within 3 hours.
• Intravenous fluids and electrolytes may be given to correct dehydration and electrolyte imbalance caused by vomiting and diarrhea.
• Oxygen therapy and mechanical ventilation may be required for patients with respiratory distress or failure due to neurotoxic effects of some toxins.
• Antihistamines, corticosteroids, or bronchodilators may be used to treat allergic reactions or bronchospasm caused by some toxins.
• Anticonvulsants may be used to control seizures caused by some toxins.
• Atropine may be used to counteract the muscarinic effects of some toxins, such as bradycardia, salivation, lacrimation, urination, and defecation.
• Mannitol may be used to reduce intracranial pressure and cerebral edema caused by some toxins, such as domoic acid.
• Hemodialysis or hemoperfusion may be used to remove some toxins from the blood, such as microcystins or cylindrospermopsin.

The prognosis of algal food poisoning depends on the type and amount of toxin ingested, the time elapsed since ingestion, the severity of symptoms, and the availability of medical care. Most cases are mild and self-limiting, but some can be fatal or cause permanent damage to the nervous system, liver, kidney, or heart. Early diagnosis and treatment can improve the outcome and prevent complications.

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