If you live in Western Australia, you may have seen recent news stories warning you not to eat seafood you’ve caught in the Swan River. If ingested (even after cooking), local fish and shellfish can cause a severe condition called paralytic shellfish poisoning (PSP), which is due to recent algal blooms in the river.
Most of our major waterways are regularly monitored for the presence of algal blooms, as some types of algae secrete toxins that are absorbed by marine creatures and then ingested by us when we eat these creatures. Currently, the concerning genus in Perth’s rivers is a type of dinoflagellate called 𝘈𝘭𝘦𝘹𝘢𝘯𝘥𝘳𝘪𝘶𝘮 𝘴𝘱𝘱, which secrete a type of alkaloid neurotoxin called a saxitoxin.
Saxitoxin is the most common cause of PSP, and 𝘈𝘭𝘦𝘹𝘢𝘯𝘥𝘳𝘪𝘶𝘮 species are found in most parts of the world. Around half a milligram of saxitoxin will kill an adult human if ingested orally; if injected, half a microgram is fatal. For perspective, one grain of sand weighs around 4 milligrams.
Like many toxins covered previously on #toxicologytuesday , saxitoxin is a potent sodium channel blocker. When ingested or administered, the toxin reversibly binds to voltage-gated sodium channels in nerve cells, blocking the passage of sodium ions into the cell. When this occurs, the cell is unable to fire action potentials, which are an important form of communication between neurons and either other neurons or other cell types. Some major consequences of this include no hormone secretion by glands and no contraction by skeletal muscle tissue. The latter, a more urgent problem, causes flaccid paralysis and respiratory arrest, as the victim is obviously unable to breathe.
After ingesting contaminated shellfish, the victim will show classic food poisoning symptoms, such as vomiting, diarrhoea and abdominal pain, after around 30 minutes. However, tingling lips and extremities, numbness, breathing difficulties and confusion accompany these symptoms. Once paralysis sets in, the victim will die of respiratory arrest unless immediate artificial ventilation is provided. There is no antidote to saxitoxin, but victims may recover with immediate medical attention. ...