BY FARHAN ZULKIPLEE
We can see sometimes the ocean, river and lakes change colour from blue to red, brown and green. This phenomenon is caused by an algae bloom.
Algae is a microorganism which will grow and proliferate when there are abundant nutrients in the water. It will rapidly multiply and changes the water colour depending on the species.This phenomenon might look fascinating but it can be harmful to animals and humans. While most algae in the water is harmless, the harmful algal bloom (HAB) can secrete or contain phycotoxin that can accumulate in the fish, crab or bivalve filter feeder (shellfish).
In shellfish, the toxin will accumulate in the digestive glands without causing any adverse effect on the shellfish itself. However, when substantial amount of contaminated shellfish is consumed by humans, it can cause severe intoxification of various kinds of shellfish poisoning that may lead to severe effect to health and even death. The toxins don’t go away even when shellfish are cooked or frozen. Here are some of the shellfish poisoning that is caused by HABs that occur around the world.
[ihc-hide-content ihc_mb_type=”show” ihc_mb_who=”2,3,5″ ihc_mb_template=”1″ ]Paralytic shellfish poisoning (PSP)
The first known effect of HABs is paralytic shellfish poisoning (PSP) that is caused by saxitoxin produced by several species of dinoflagellates. Saxitoxins are a kind of neurotoxin compound that is 1,000 times more potent in toxicity than cyanide and have a high mortality case. When ingested it causes peripheral parenthesis, nausea, vomiting, diarrhoea, ataxia, weakness, shortness of breath and could potentially and rapidly cause progressive muscle paralysis and respiratory arrest.
Amnesic shellfish poisoning (ASP)
Amnesic shellfish poisoning, is caused by domoic acid. Domoic acid is a neurotoxin that binds with glutamate receptors affecting the hippocampus, which is involved in processing memory and visceral functions in the brain. The symptoms include dizziness, headache, seizures, disorientation, short-term memory loss, respiratory difficulty, and coma.
Diarrhoeic shellfish poisoning (DSP)
Diarrhoeic shellfish poisoning (DSP) is an acute gastrointestinal illness caused by consumption of bivalve molluscs that have accumulated okadaic acid. Okadaic acid is a naturally occuring marine toxin, called “biotoxin,” that is produced by microscopic algae, specifically, the dinoflagellate Dinophysis. The acid causes long-lasting contraction of smooth muscle from human arteries causing nausea, vomiting, abdominal pain, and diarrhoea being the most commonly reported symptom.
Neurologic shellfish poisoning (NSP)
Neurologic shellfish poisoning (NSP) is caused by polyether brevetoxins produced by the unarmoured dinoflagellate Gymnodinium breve An unusual feature of Gymnodinium breve is the formation by wave action of toxic aerosols which can lead to asthma-like symptoms in humans.
Adverse effects observed are diarrhoea, vomiting, cramps, rapid reduction of the respiratory rate and cardiac conduction disturbances which can lead to coma and eventually to death. Inhalation of brevetoxin aerosols may result in respiratory problems, eye and nasal membrane irritations.
Azaspiracid shellfish poisoning (AZP)
Although the symptoms of this kind of poisoning resembles those of diarrhoeic shellfish poisoning (DSP), concentrations of the major DSP toxins were very low in the mussel extracts. Eventually the toxin, azaspiracid, was identified and the new toxic syndrome was called azaspiracid poisoning (AZP). It is not readily known, how this poison acts its compound is not yet fully understood but the effects such as gastrointestinal disorder, diarrhoea and abdominal cramps are observed during AZP intoxication.
Ciguatera food poisoning (CFP)
At present, ciguatera food poisoning is the most common type of marine food poisoning worldwide and it constitutes a global health problem. The ciguatoxins accumulate through the food chain, from small herbivorous fish grazing on the coral reefs into organs of bigger carnivorous fish that feed on them. The first symptoms can be either gastrointestinal or neurological in nature. The symptoms typically last for several weeks to several months and in some cases, it may persist for years. But this does not prove that we should avoid eating fish and shellfish now. We just need to control how much we eat it and how often to avoid getting this poisoning. Another thing, always check if there are any restriction or warning from the authorities that state if there are harmful algae bloom occurring around the region to avoid eating contaminated marine food.
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