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Alexandrium spp. (al-eh-k-ZAND-ree-uhm)
Species Distribution: A number of species of the dinoflagellate Alexandrium produce saxitoxin and related congeners. Although various species of
Alexandrium have been reported in temperate oceans worldwide, potentially toxic species have been observed along the northeast and west coasts of
North America and in the Canadian maritime provinces.
Toxins/Mode of Action: Saxitoxin (STX) and Congeners
The toxins responsible for paralytic shellfish
poisoning consist of a suite of heterocyclic guanidines collectively called saxitoxins.
Saxitoxin binds with voltage dependent sodium channel, inhibiting channel opening. The
voltage dependent sodium channel plays a critical role in neurotransmission at both the neuronal synapses and
neuromuscular junctions. The primary site of STX action in humans is most likely at the neuromuscular junction, thus inhibiting nerve conduction.
Human Health Syndrome: Paralytic Shellfish Poisoning (PSP)
Paralytic shellfish poisoning produces symptoms consumption of contaminated
shellfish. In mild exposures, symptoms include tingling sensations or numbness, headaches, fever, rash, dizziness, and gastrointestinal illness. In severe cases
symptoms include muscular paralysis, pronounced respiratory difficulty, and choking sensation. Despite the severity of this toxin victims begin to recover
within 12-24 hours of intoxication. In some severe cases death may occur through paralysis and respiratory failure. Learn more about paralytic shellfish toxins in an excerpt from Diversity of Marine and Freshwater Algal Toxins
Species Associated With PSP:
- Alexandrium caternella
- Alexandrium tamarense
- Alexandrium fundyense
- Alexandrium minutum
- Gymnodinium catenatum
- Pyrodinium bahamense var. compressum
Syndrome Distribution: PSP was first confirmed in 1948 on the coast of Japan. In the 1960s and the early 1970s Japan continued to see outbreaks of PSP and new cases were confirmed in Malaysia, the Philippines, Indonesia, Australia, and North America. The United States has reported persistant problems with cases of PSP along both west and northeast coasts since the mid 1960s. In the early 1980s, various countries within Europe also began to report cases of PSP.
