Thursday 31 October 2013

A bad lashing

Chironex fleckeri  the sea-wasp, a variety of box-jellyfish, is billed as the most poisonous animal in the sea, and that it has taken more human lives than sharks, stone-fish and crocodiles combined. It was brought to my attention this week by the interview with Tom and Dorothy Cross.  Wikipedia offers "The amount of venom in one animal is said to be enough to kill 60 adult people".  Which is not really useful except in the sense of a teacupful of botulinum toxin could kill 1-2 billion people IF it was carefully aliquoted out and distributed on a ng/kg basis to a very long queue of people.  I've looked at such lines of people before at events in the Baltics and Catalonia.  The Botox event would have a queue going 40 times round the world at the equator.  Which is a packing problem similar to the fact that each human cell 30 microns across has 2 m of DNA coiled inside.

The sea-wasp makes its living actively hunting through the seas of Northern (tropical) Australia.  It trails out tentacles loaded with nematocysts, cells which turn themselves inside out when they brush against things that feel and smell right - primarily small fish and shrimps.  This response deposits a tiny poison dart into the prey; as it struggles the tentacles wrap round and deliver more darts. The biomechanics happens really fast "The venom is fired into the skin within 3 milliseconds of being triggered – 10 times faster than the inflation of an airbag in a car crash".  And the biochemistry is zippy as well: within minutes the dead protein is brought into the head of the jellyfish where it is digested . . . in full view because the sea-wasp is pretty much transparent.  

The contents of the nematocyst pay-load is a mix including a pair of largish proteins A7L035 and A7L036. These two are 73% identical and less closely related to other cnidarian toxins but the protein family has no known antecedents or distant cousins.  Like the nematocyst itself, these toxins are unique to cnidarins. Despite their evolutionary distance from other proteins, it looks like there are a few (just possibly seven but I don't really believe my own analysis on that one) transmembrane helixes in their structure. It is therefore possible that their mode of action is to make channels in the cells of their victims and disrupt the delicate homeostatic balance of what's inside and what's out.  However it works, they have a devastating effect on shrimp, fish and humans who get an armful.  They jangle your nociceptors so you feel a intense pain; cardiac arrhythmia follows; then respiratory distress; wild fluctuations in blood-pressure also occur; on a microscopic level you can see some cells burst open; and on a molecular level there is some elevation of potassium. 

But, since records began in 1884, there have only been 64 deaths recorded: most of them children.  Which is about a third of the road deaths in Ireland last year.  So we don't need to worry too much about death but the survivors of a C fleckeri lashing are deeply unhappy - from the pain and from the disfiguring scars of massive local necrosis where the delicate tendrils brushed against you. Like with road traffic accidents we only record and compare the deaths but ignore the far greater number of people who are "merely" injured.

Advice to young Irish people before they emigrate to Australia.
Go to Adelaide or Ballarat rather than Cairns or Darwin. Be a man! Men are hairier than women and children and this can minimise contact with nematocysts which are fast but very short range. Wear clothing - any clothing, tights will give you significant protection.   Research when C fleckeri comes inshore - it's seasonal - and don't go swimming then. Don't whip your arm away quickly - it will ensure more contact.  Don't reach down to your leg when you feel the first stab of excruciating pain - your arms are more useful to you than your legs.  Don't panic.  Don't run about screaming - it will hasten the delivery of the toxins to your heart and lungs. When you get to shore don't pull off the tentacles until you've neutralised the nematocysts with vinegar - pulling will activate the remaining motion-sensitive nematocysts.  Wash off with salt- rather than fresh water.  If it's your child, it's better to pick off the neutralised tentacles with the thick pads of your fingers.  
Just stay in Ireland?

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