Coumaphos: delayed neurotoxic effect following dermal administration in hens

This study reports the differential neurotoxic effects of coumaphos [O,O-diethyl O-(3-chloro-4-methyl-7-coumarinyl) phosphorothioate] when applied orally or dermally in the adult hen. Dermal administration of single (50-500 mg/kg) or daily (100 mg/kg) doses resulted in delayed neurotoxicity in hens, similar to that caused by other delayed neurotoxic organophosphorus compounds. Coumaphos caused loss of weight and produced ataxia, which progressed to paralysis and death. Degeneration of axons and myelin in the spinal cord was the most consistent histopathologic alteration and was identical to that reported for other delayed neurotoxic organophosphorus esters. Only one hen showed peripheral nerve degeneration. Oral administration of a single 100 mg/kg dose or daily doses of 10 mg coumaphos caused severe acute toxicity and killed all treated hens 1-8 d. These hens did not develop delayed neurotoxicity. Some hens given a single oral 50-mg/kg dose or daily 5-mg/kg doses of coumaphos recovered from the initial cholinergic effect and developed clinical signs of delayed neurotoxicity. These hens, however, improved with time and did not show unequivocal nervous-tissue damage at termination.