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Title: Efficacy of imidocarb dipropionate in the elimination of Theileria equi in experimentally infected horses

Author
item GRAUSE, JUANITA - Animal And Plant Health Inspection Service (APHIS)
item Ueti, Massaro
item NELSONA, JEFFREY - Animal And Plant Health Inspection Service (APHIS)
item Knowles Jr, Donald
item Kappmeyer, Lowell
item BUNN, THOMAS - Animal And Plant Health Inspection Service (APHIS)

Submitted to: The Veterinary Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2012
Publication Date: 11/28/2012
Citation: Grause, J.F., Ueti, M.W., Nelsona, J.T., Knowles Jr, D.P., Kappmeyer, L.S., Bunn, T.O. 2012. Efficacy of imidocarb dipropionate in the elimination of Theileria equi in experimentally infected horses. The Veterinary Journal. 10.1016/j.tvjl.2012.10.025.

Interpretive Summary: Theileria equi, one of the causative agents of equine piroplasmosis, is endemic worldwide but is considered an exotic animal disease in the United States. In an effort to exclude T. equi, the U.S. practices stringent serological screening of horses prior to entry. Current regulatory options available in cases of infected U.S. horses include permanent quarantine, exportation, or euthanasia. Chemotherapeutics that eliminate infection and subsequently transmission risk are a critical need for management of infected horses. In this study, we demonstrated the efficacy of imidocarb dipropionate against experimental T. equi infection. Nine horses were experimentally inoculated with T. equi isolated from an infected horse previously imported from Peru, and six of these were treated with imidocarb after the resolution of acute disease. Elimination of T. equi was demonstrated in all but one horse by the following tests: nested PCR at multiple time points, blood transfer from treated into naïve horses, and reversion to seronegative status.

Technical Abstract: Theileria equi, one of the causative agents of equine piroplasmosis, is endemic in many regions of the world but is considered a foreign animal disease in the United States. In an effort to exclude T. equi, the U.S. practices stringent serological screening of horses prior to entry. Current regulatory options available in cases of infected domestic horses include permanent quarantine with or without chemotherapy, exportation, or euthanasia. Chemotherapeutics that eliminate infection and subsequently transmission risk are a critical need for management of infected horses. In this study, we sought to determine efficacy of imidocarb dipropionate against experimental T. equi infection. Nine horses were experimentally inoculated with T. equi isolated from an infected horse previously imported from Peru, and six of these were treated with imidocarb dipropionate after the resolution of acute disease. Elimination of T. equi was demonstrated in all but one horse by the following tests: nested PCR, intravenous blood transfusion from treated to naïve horses, and reversion to seronegative status. These data show imidocarb dipropionate was capable of eliminating T. equi infection in five of six experimentally infected horses.