Dermatological and parasitological evaluation of infestations with chewing lice (Werneckiella equi) on horses and treatment using imidacloprid.

Lice infestations in horses caused by the chewing louse Werneckiella (Damalinia) equi are observed worldwide. In the present study, the efficacy of 10% imidacloprid was tested on horses naturally infested with lice. Two groups of animals received a double application of 4 ml and 8 ml Advantage 10% spot-on on day 0 and 28 either. Horses, presenting dermatological signs with negative lice counts, were also included in this investigation. 40.86% of the horses presented positive lice counts and 84.21% of these animals showed clinical dermatologic signs. 65.45% of the lice-negative horses also showed clinical manifestations. Two days after treatment, lice counts dropped in both the treatment groups and on day 56, all animals were free of alive lice, and dermatological lesions decreased significantly (P<0.001) in both the lice-positive and the negative animals. No correlation (P>0.050) between lice burden and clinical signs was detected.