Today I am once again going to talk about my honest opinions on ragwort. It includes an example of a discussion where an equine vet got things wrong on ragwort. This happened on Facebook earlier in the week and I have given her enough time to respond so I think I should now share this encounter so that you can all see the problem.
As regular readers will know it isn't the first time there has been an issue with what an equine vet has said. I do wonder if they are taught all I would expect them to be taught.
The issue in question here is whether you can diagnose ragwort poisoning with certainty. My view on this is, after having read the literature, you cannot. It is quite simple really. There are characteristic symptoms of damage which can be observed under a microscope, but while those symptoms are characteristic of pyrrolizidine alkaloid poisoning caused by the toxins in ragwort, that is not their only cause. Another cause is damage by toxins produced in invisibly mouldy hay.
Since you have more than one cause it is surely not possible to say that the damage is caused by one of them.
Although it doesn't seem to be the problem in this specific case there is also the issue of vets doing blood tests which are just indicative of liver damage from any of a number of causes. I got four letter insults from one equine charity which insisted that veterinary blood test results proved ragwort poisoning on twitter.
Naturally as a specialist on ragwort I do keep up on the latest scientific literature if I can and there is a paper published just last month that contains some interesting quotes.
"Outbreaks of hepatic disease are common and once often were suspected to be caused by pyrrolizidine alkaloid (PA) toxicosis, although more recent evidence suggests that PA toxicity is far less common than generally suspected."
Pyrrolizine alkaloid toxicosis is what happens in ragwort poisoning so the recent evidence suggests it is far less common than had been assumed. I've explained the exaggerations and nonsense statistics in previous postings.
"We found that mycotoxins were present in >80% of hay samples fed to horses in the United Kingdom."
Now not all of them were the kind of mycotoxins that might be confused with ragwort poisoning on biopsy but we do know as I said above that this is assumed without biopsies.
"Interestingly, although not a specific finding, scattered individual hepatocyte necrosis and apoptosis are the most common histopathologic features in liver biopsy specimens collected from horses involved in outbreaks of liver disease in the United Kingdom."
This is very significant because we can be sure what ever the cause that this shows that most cases are not ragwort poisoning, something which had been in print previously, but confirmed again here.
Well, here is the conversation on Facebook. The quotes given are not the only source of information that I have to confirm this. In case you're wondering my responses were in paragraphs. There is a way to do this on Facebook postings where normally pressing enter creates a posting, causing postings to be rather unclear.
Harriet Kate Fairhurst
Patrick Anthony Thirkell unfortunately, as an equine vet, I personally put to sleep 3 horses last year due to ragwort ingestion, causing irreversible damage to the liver. ingestion of ragwort causes Pyrrolizidine alkaloid toxicity, the alkaloids in toxic plants (such as ragwort) cause a primary toxic effect on liver parenchyma, leading to enlargement of liver cells, leading to impairment of cell division, resulting in large bits of the liver then being unable to function, ultimately leading to hepatic failure and death. There are many plants which cause it, however ragwort is the main perpetrator.
Bill Ellson
Harriet Kate Fairhurst How do you distinguish between liver failure caused by ragwort and liver failure caused by mycotoxins?
Harriet Kate Fairhurst
Bill Ellson ragwort poisoning specifically causes changes in liver cells termed megakaryocytes. On histology slides of a liver biopsy, these are very specific for ragwort poisoning.
Bill Ellson
Harriet Kate Fairhurst Really? Any peer reviewed science that supports that assertion
Neil Jones
Harriet Kate Fairhurst I honestly believe you are wrong.
First of all I think you'll find that megakaryocytes are bone cells responsible for
creating the platelets in blood.
I think you mean megalocytosis. Bill Ellson asked how you tell ragwort poisoning from poisoning by mycotoxins. Aflatoxins are mycotoxins and produce the same characteristic microscopic changes,
Indeed we know from the biochemistry why this happens and why they cannot be distinguished.
If more than one cause exists for an effect, then you cannot surely describe the effect as due to just one of those causes
A few excerpts from the literature:
"Hepatic megalocytosis can be observed in some aged animals, but is characteristic lesion observed in toxic insult by pyrrolizidine alkaloids and aflatoxins. " From Veterinary Toxicology Basic and Clinical Principles
"Hepatic megalocytosis is observed with certain toxic insults, particularly pyrrolizidine alkaloid toxicosis and aflatoxin toxicosis. " from Clinical Veterinary Toxicology.
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