OVER the past couple of months we’ve seen a handful of very odd, but related, neurological cases in animals as diverse as a black-headed caique, cats and a bulldog.
All were exhibiting strange behaviour, including poor co-ordination, weakness, muscle tremors and depression. In two dogs, the first sign was vomiting.
What these patients had in common was that all had recently been treated with products containing tea tree oil (melaleuca oil), either shampoos or insecticidal spot-ons.
Treatment involved washing residual amounts of oil from their skin and using activated charcoal to reduce the absorption of the oil in the gut. While the parrot and dogs recovered quickly, the two cats needed two to three days of care.
It is likely that the toxic effects of the oil occur when the product is ingested, probably when an animal grooms itself.
These cases took many of us by surprise, after all tea tree oil is found widely in pet shampoos and skin preparations. We consulted the Veterinary Poisons Information Service (VPIS) for advice and have been back in touch to report the outcomes.
The VPIS database has recorded 55 cases where the outcome of treatment is known (and many more when it is not). Only one involved a bird (ours). Thirty-five cases were dogs, all of which recovered. The remaining 19 were cats — four did not have any symptoms, eight recovered, one still had symptoms after several days, and four sadly died.
Cats may be more sensitive to essential oil toxicity because they are less able to process these chemicals in their livers. Also, cats are more likely to ingest oils when they groom. It is also possible that the presence of dermatitis (inflamed skin) in cats with a heavy flea infestation may increase absorption, and it is these animals that are more likely to be treated with shampoos or spot-ons in the first place.
Many animals are bathed in shampoos containing tea tree and other essential oils and never exhibit any adverse symptoms so the cases appear to be quite rare, but I think that at the very least an animal should be rinsed thoroughly after being bathed and extra care should be taken to follow carefully the instructions. None of the prescription spot-ons available from us have tea tree oil in them. It is always advisable to contact us for advice if you are worried that your pet has a skin condition.
(Some of the information comes from a paper by Genovese et al., 2012 which looked at adverse effects in cats and dogs from essential oils. Thanks to the VPIS for this reference).
Director and Senior Vet