The Harmful Algae Page

Human Illness Associated with Harmful Algae


Man is exposed principally to the naturally-occurring toxins produced by harmful algae through the consumption of contaminated seafood products. The most significant public health problems caused by harmful algae are:

Each of these syndromes are caused by different species of toxic algae which occur in various coastal waters of the US and the world. With the increase in interstate and international transport of seafood, as well as international travel by seafood consumers, there are virtually no human populations that are free of risk. Since 1978, illnesses in the US due to natural algal toxins have included PSP, NSP, CFP, and ASP. No incidents of DSP have yet been verified in this country. Although records are incomplete because reporting to the Centers for Disease Control (CDC) is voluntary, evidence indicates that ciguatera was responsible for about half of all seafood intoxications. A growing body of evidence indicates that incidents of ASP are on the increase and that DSP may shortly make its debut in the United States, since the causative organisms occur throughout the temperate coastal waters of the US.


Amnesic Shellfish Poisoning (ASP)

causative organisms: Pseudo-nitzschia sp.

toxin produced: Domoic Acid

ASP can be a life-threatening syndrome. It is characterized by both gastrointestinal and neurological disorders (Bates et al., 1989). Gastroenteritis usually develops within 24 hours of the consumption of toxic shellfish; symptoms include nausea, vomiting, abdominal cramps, and diarrhea. In severe cases, neurological symptoms also appear, usually within 48 hours of toxic shellfish consumption. These symptoms include dizziness, headache, seizures, disorientation, short-term memory loss, respiratory difficulty, and coma. In 1987, four victims died after consuming toxic mussels from Prince Edward Island, Canada. Since that time, Canadian authorities have monitored both the water column for the presence of the causative diatom, and shellfish for the presence of the toxin, domoic acid. Shellfish beds are closed to harvesting when the domoic acid concentration reaches 20 µg/g shellfish meat. Fish and crab viscera can also contain domoic acid, so the risk to human consumers and animals in the marine food chain is more significant than previously believed.

Additional information on ASP:

General Background - Clinical Presentation - Diagnosis - Management and Treatment -
Chemical Structure - Molecular Mechanism of Action - References - Poison Control Marine Hotline


Ciguatera Fish Poisoning (CFP)

causative organisms: Gambierdiscus toxicus, Prorocentrum spp., Ostreopsis spp., Coolia monotis, Thecadinium sp. and Amphidinium carterae

toxins produced: Ciguatoxin/Maitotoxin

CFP produces gastrointestinal, neurological, and cardiovascular symptoms. Generally, diarrhea, vomiting, and abdominal pain occur initially, followed by neurological dysfunction including reversal of temperature sensation, muscular aches, dizziness, anxiety, sweating, and a numbness and tingling of the mouth and digits. Paralysis and death have been documented, but symptoms are usually less severe although debilitating (Miller, 1991). Recovery time is variable, and may take weeks, months, or years. Rapid treatment (within 24 hours) with manitol is reported to relieve some symptoms. There is no antidote, supportive therapy is the rule, and survivors recover. Absolute prevention of intoxication depends upon complete abstinence from eating any tropical reef fish, since there is currently no easy way to measure routinely ciguatoxin or maitotoxin in any seafood product prior to consumption.

Additional information on CFP:

General Background - Clinical Presentation - Diagnosis - Management and Treatment -
Chemical Structure - Molecular Mechanism of Action - Poison Control Marine Hotline

Diarrhetic Shellfish Poisoning (DSP)

causative organisms: Dinophysis sp.

toxin produced: Okadaic Acid

DSP produces gastrointestinal symptoms, usually beginning within 30 min to a few hours after consumption of toxic shellfish (Yasumoto and Murato, 1990). The illness, which is not fatal, is characterized by incapacitating diarrhea, nausea, vomiting, abdominal cramps, and chills. Recovery occurs within three days, with or without medical treatment.

Additional information on DSP:

General Background - Clinical Presentation - Diagnosis - Management and Treatment -
Chemical Structure - Molecular Mechanism of Action - References - Poison Control Marine Hotline




Neurotoxic Shellfish Poisoning (NSP)

causative organism: Karenia brevis

toxins produced: Brevetoxins

NSP produces an intoxication syndrome nearly identical to that of ciguatera. In this case, gastrointestinal and neurological symptoms predominate. In addition, formation of toxic aerosols by wave action can produce respiratory asthma-like symptoms. No deaths have been reported and the syndrome is less severe than ciguatera, but nevertheless debilitating. Unlike ciguatera, recovery is generally complete in a few days. Monitoring programs (based on K. brevis cell counts) generally suffice for preventing human intoxication, except when officials are caught off-guard in previously unaffected areas.

Additional information on NSP:

General Background - Clinical Presentation - Diagnosis -
Management and Treatment - Molecular Mechanism of Action - References -
Poison Control Marine Hotline

Paralytic Shellfish Poisoning (PSP)

causative organisms: Alexandrium spp.,Gymnodinium catenatum, Pyrodinium bahamense

toxins produced: Saxitoxins

PSP, like ASP, is a life threatening syndrome. Symptoms are purely neurological and their onset is rapid. Duration of effects is a few days in non-lethal cases. Symptoms include tingling, numbness, and burning of the perioral region, ataxia, giddiness, drowsiness, fever, rash, and staggering. The most severe cases result in respiratory arrest within 24 hours of consumption of the toxic shellfish. If the patient is not breathing or if a pulse is not detected, artificial respiration and CPR may be needed as first aid. There is no antidote, supportive therapy is the rule and survivors recover fully. PSP is prevented by large-scale proactive monitoring programs (assessing toxin levels in mussels, oysters, scallops, clams) and rapid closures to harvest of suspect or demonstrated toxic areas.

Additional information on PSP:

General Background - Clinical Presentation - Diagnosis - Management and Treatment -
Chemical Structure - Molecular Mechanism of Action - References -
Poison Control Marine Hotline


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