Some toxicity aspects of dichlorvos flea collars in cats

The effects of the application of a single dichlorvos flea collar containing 500 mg of the insecticide were observed in 23 growing cats for periods of from 1 to 15 weeks. No overt signs of toxicity occurred and weight gain in young growing animals was not significantly affected. Whole blood cholinesterase was reduced within the first week of application of the collar and remained below pretreatment levels for 5 to 8 weeks before returning to normal presumably as the insecticide concentration in the resin was progressively reduced. Signs of systemic organophosphate toxicity did occur within 1 week of the application of three collars to each of two cats kept in the same cage. This suggested that the likelihood of toxicity occurring in cats following the use of dichlorvos flea collars depended mainly on the degree of exposure to the insecticide. Considering recent reports in the literature it was proposed that the environmental conditions of temperature (11 degrees to 23 degrees C) and relative humidity (50 to 65%) under which the experiments were carried out would have promoted a relatively low atmospheric concentration of dichlorvos in the near environment of the test animals and hence generally prevented occurrence of clinical signs. Under most conditions of keeping domestic cats in Australia the use of a single dischlorvos flea collar should therefore be without any untoward effect although some initial and transient inhibition of whole blood and nervous tissue cholinesterases would be expected.