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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Friday 10th February 2012

A story from China makes me think I shall have to change what I say about deaths due to toxic fungi. It also made me think about Paracelsus and rhubarb.

The report said that researchers had discovered a fungus to be the cause for what was known as ‘Yunnan Sudden Unexpected Death’, a condition believed to have claimed over 260 lives in the past 30 years. Now, 260 deaths over 30 years is not a huge toll but it, probably, means I should stop saying that deaths from toxic mushrooms are ‘extremely rare’ and substitute ‘very rare’ or ‘quite rare’.

The idea of a geographically discrete medical condition is not new. I’ve written quite a lot about Balkan endemic nephropathy (BEN) both on the Aristolochia clematitis page and in blog entries here and here. In that case, the unusually high incidence of serious kidney disease was, finally, discovered to be because subsistence farmers were not removing birthwort growing amongst their wheat before harvesting and the seeds were being milled into flour with the wheat.

Now that the kidney disease has been attributed to plant poisoning, the condition is known as aristolochic acid nephropathy (AAN). The same condition has also been found in people using Chinese herbal remedies containing extracts from the plant.

I wonder if ‘Yunnan Sudden Unexpected Death’ will now be renamed. Initially, research in the area discovered a new fungus that was named Trogia venenata and established that, as far as could be determined, ingestion of the mushroom was a common factor in the sudden deaths of apparently healthy villagers in the Yunnan province. The conclusion that the mushroom was the cause of these deaths seems to be supported by the fact that, since 2009 when villagers were warned against eating these mushrooms, there have been no deaths.

The new report is that researchers say that have isolated the toxic components and synthesised them to have enough to conduct a trial in mice that proves the lethality of the compounds. So, we have the physical evidence of an apparent end to the deaths now coupled with the scientific proof of the toxicity of the compounds found in the mushrooms. Job done, right?

Well, maybe not, and here’s where Paracelsus and rhubarb, usually from varieties of the domestic Rheum x hybridum, come in. Because other experts on toxic fungi have questioned whether there is enough of the toxic amino acids in the mushrooms to be lethal. One has calculated that it would require the consumption of 4kg of the mushrooms to produce fatal poisoning.

Paracelsus had quite a bit to say about the nature of poison and it is often précised as ‘the dose makes the poison’. For example, we know that quite a few of the people who are reported to have died as a result of taking ecstasy actually died from drinking too much water to overcome the dehydration said to result. Water is a poison – if you have enough of it. So, if people aren’t eating 4kg of mushrooms, assuming that is the lethal dose, do we know why they are dying?

The rhubarb comparison comes because it is often said that oxalic acid in rhubarb leaves is what makes them potentially fatal. But post mortem examinations have shown that the concentration of the metabolites of oxalic acid is too low for that to be the cause of death. Anthraquinone alkaloids are suspected of being the true cause though I’m not aware of anyone doing the work required to confirm this. That may be because, as long as people know that rhubarb leaves can be fatal and avoid eating them, there is no reason, other than pure scientific interest, to conduct the research.

As long as the people in Yunnan accept that Trogia venenata is to be avoided then queries about the exact mechanism are irrelevant. Unless, that is, someone argues that since science can’t precisely define what makes the mushroom a killer it means that it is not a killer and people are encouraged to continue eating them.

Going back to Aristolochia clematitis, there are those who dispute the science and claim that the case against using extracts from the plant in Traditional Chinese Medicine is politically motivated and seeks to undermine cultural heritage. They continue to offer remedies that are, almost certainly, destroying people’s kidneys.