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Mistletoe Ingestion

I had a friend ask if Mistletoe is poisonous.

Gary Pfalzbot (GoatWorld): This is a good question. I've looked everywhere for the connection of Mistletoe being poisonous to goats and have found nothing to indicate that it is. This is without researching the actual chemical components of the plant. However, Mistletoe is considered poisonous (berries and leaves) to humans, dogs, cats and certain exotic birds. Mistletoe is actually a parasitic plant which grows on a host such as a pecan tree, apricot tree, black walnut tree, etc. I seem to recall that throughout the years, many people have considered this plant to be poisonous so I think just to be on the safe side, I wouldn't allow goats to eat it. It is perhaps one of those plants that is mildly toxic and produces side effects such as gastrointestinal difficulties. I will research this further and post the conclusive findings in the GoatWorld Poisonous Plant section.

I am going to venture out on a limb here and say that Mistletoe is probably at least "mildy toxic" because it contains glycosides but perhaps not fatal. In reading the findings of this report (that were largely based upon human consumption), it might be reasoned that "some" goats may incur difficulties ingesting mistletoe, others may not. The same can be said of the poison oak, ivy and sumac classes of plants. Some goats (and humans) will incur effects, others may not. There is no data pertinent to ingestion and the effect on dairy animals. Here is the report I found:

Spiller HA Willias DB Gorman SE Sanftleban J
Retrospective study of mistletoe ingestion.
In: J Toxicol Clin Toxicol (1996) 34(4):405-8
ISSN: 0731-3810

BACKGROUND: There are limited data concerning accidental exposure to Phoradendron flavescens (Phoradendron serotinum, American Mistletoe). The only published reports include a review of 14 cases which revealed no symptoms and a single fatality from an intentional ingestion of an unknown amount of an elixir brewed from the berries. The risk of serious toxicity from accidental exposure to this plant appears to be minimal, yet it continues to be regarded as a dangerous plant. We reviewed charts for four years (1990-1993) from three poisoncenters where Phoradendron flavescens is indigenous.

RESULTS: Ninety-two human cases were located. Age ranged from four months to 42 years, with a mean of six years (SD 8.8) and median of two years. There were 14 symptomatic cases of which 11 were determined to be related to mistletoe exposure. There were six gastrointestinal upset, two mild drowsiness, one eye irritation, one ataxia (21 months), one seizure (13 months). Treatments included gastrointestinal decontamination in 54 patients (59%), ocular irrigation in one and IV benzodiazepine in one. Decontamination did not appear to affect outcome. Amount ingested ranged from one berry or leaf to more than 20 berries or five leaves. In cases with a known amount ingested, eight of ten cases with > or = 5 berries remained symptom free. In the 11 cases with leaf-only ingestion (range 1-5 leaves), three patients had gastrointestinal upset. The one case with five leaves ingested remained asymptomatic. The infant with seizures was an unwitnessed exposure, found with both berries and leaves in the crib. No arrhythmias or cardiovascular changes were reported in any case. All symptomatic cases had onset of symptoms in < or = 6 hours.

DISCUSSION: Symptoms are infrequent and in all but one case would not require direct medical supervision. Seizures have not previously been reported with Phoradendron flavescens exposure.

CONCLUSION: Symptoms from Phoradendron flavescens exposure are infrequent, even with ingestion of 5-20 berries or 1-5 leaves, but may include seizures. Cardiovascular effects were not seen.


*****FEBS LETTERS*****Endo Y Oka T Tsurugi K Franz H The mechanism of action of the cytotoxic lectin from Phoradendron californicum: the RNA N-glycosidase activity of the protein. In: FEBS Lett (1989 May 8) 248(1-2):115-8
ISSN: 0014-5793

A toxic lectin from Phoradendron californicum (PCL) was found to inactivate catalytically 60 S ribosomal subunits of rabbit reticulocytes, resulting in the inhibition of protein synthesis. To study the mechanism of action of PCL, rat liver ribosomes were treated with the toxin and the extracted rRNA was treated with aniline. A fragment containing about 450 nucleotides was released from the 28 S rRNA. Analysis of the nucleotide sequence of the fragment revealed that the aniline-sensitive phosphodiester bond was between A4324 and G4325 of the 28 S rRNA. These results indicate that PCL inactivates the ribosomes by cleaving an N-glycosidic bond at A4324 of 28 S rRNA in the ribosomes as does ricin A-chain.

Registry Numbers:EC 3.2.2. (Nucleosidases) EC 3.2.2.- (RNA N-glycosidase)

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