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VOL. 72 (3), 391-408, 2006 HARMFUL ALGAL BLOOMS, RED TIDES AND HUMAN...

(DSP), and amnesic shellfish poisoning (ASP). Toxins produced by
harmful species are transferred to food chain throughout filtering
organism and can remain active within them for long time. Briefly,
the causative toxin responsible of PSP is saxitoxins (SXTs) and is
produced by dinoflagellates Alexandrium spp., Gymnodinium
catenatum, and Pyrodinium bahamense. These toxins can be divided
in two groups: SXTs 5-18 and neosaxitoxins 19-27. STXs are specific
and potent agents that block the sodium channels in neuronal and
muscular tissue, which prevents propagation of the action potential.
The clinical profile is mainly neurological and their onset is rapid
(within 30 minutes), there is a tingling or numbness around the lips,
in the face and neck, a prickly sensation in the fingertips, headache,
fever, nausea, vomiting and diarrhoea. The most severe cases result
in respiratory arrest within 24 h of consumption of the toxic shellfish
(mussels, oysters, scallops, clams). There is no antidote at the
moment, only supportive therapy.

The intoxication caused by domoic acid and its congeners
denominated ASP is produced by diatoms Pseudonitzschia pungens f.
multiseries, P. australis, P. pseudodelicatissima, P. seriata, Nitzschia
actydrophila, Amphora coffeiformis. The toxin, an excitatory amino
acid, acts as an agonist to glutamate receptor (16), which conducts
Na+ ion channels inducing depolarisation increasing the Ca+ ion
permeability, which leads to cell death. Symptoms include
gastroenteritis (within 24 h of the consumption of toxic shellfish)
and in severe cases, neurological symptoms also appear, usually
within 48 h. Dizziness, headache, disorientation, short-term memory
loss, respiratory difficulty and coma are also observed (17).

Ciguatoxins (CTXs) and Maitotoxin (MTX) are the agents
responsible for the CFP. The main causative organism is
Gambierdiscus toxicus, an epiphytic dinoflagellate that produce a
group of lipid-soluble toxins (polycyclic ethers) CTXs 28-37 and
gambierol 38 (18). CFP affects more than 50,000 people annually,
caused by ingestion of coral reef fishes. Ciguatoxins are potent
neurotoxins, which act by binding quasi-irreversibly to site 5 on
sodium channels, a site overlapping the brevetoxin binding site (19),
causing them to open and modifying the sodium current. Several
effects are consequently observed at motor nerve terminals (20).
Ciguatera fish poisoning (CFP) produces gastrointestinal,

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