Delayed neurotoxicity resulting from administration of leptophos to the comb of domestic fowl.

We investigated the occurrence of delayed neurotoxicity in domestic fowl following percutaneous application of leptophos. Five groups of 5 adult hens received daily percutaneous doses of 1.0 ml/hen of leptophos emulsion (leptophos; 340 mg/hen/day) for 2, 5, 10, 15 or 20 days. There was no abnormal gait in the 2-day group. Two out of 5 hens in the 5-day group showed mild ataxia from about 2 weeks after the final administration, but did not develop severe neuropathy. On the contrary, 4 out of 5 birds in the 10-day group and all hens in the 15- and 20-day groups were affected by various stages of neurotoxicity. Some of them died from neurotoxicity. Ten of young male chickens were given the same dermal dose for 5 or 10 days. Although no abnormal chicken was observed in the 5-day group, all chickens in the 10-day group showed severe paralysis and two of them died. We studied the incidence rates of delayed neurotoxicity resulting from respective applications of the emulsion and the acetone solution of leptophos. No significant difference was observed between them. These results suggest that the daily dermal application of the relatively high dose of leptophos, even if for the short term, can cause the same delayed neurotoxic effects as by the oral administration in hens or chickens.