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Title: Imidocarb dipropionate clears persistent Babesia caballi infection with elimination of transmission potential

item SCHWINT, O - Washington State University
item UETI, MASSARO - Washington State University
item PALMER, GUY - Washington State University
item Kappmeyer, Lowell
item HINES, MELISSA - Washington State University
item CORDES, R - Animal And Plant Health Inspection Service (APHIS)
item Knowles Jr, Donald
item Scoles, Glen

Submitted to: Antimicrobial Agents and Chemotherapy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2009
Publication Date: 10/1/2009
Citation: Schwint, O.N., Ueti, M.W., Palmer, G.H., Kappmeyer, L.S., Hines, M.T., Cordes, R.T., Knowles Jr, D.P., Scoles, G.A. 2009. Imidocarb dipropionate clears persistent Babesia caballi infection with elimination of transmission potential. Antimicrobial Agents and Chemotherapy. 53(10):4327-4332.

Interpretive Summary: Infection of horses with the parasites (Babesia caballi and/or Babesia equi) are significant impediments to horse health and international movement and commerce. These data show that treatment of horses infected with Babesia caballi with imidocarb dipropionate at a dose of 4mg/kg body weight removed the parasite and eliminated transmission potential from tick transmission and direct needle transfer of blood.

Technical Abstract: Antimicrobial treatment of persistent infection to eliminate transmission risk represents a specific challenge requiring compelling evidence of complete pathogen clearance. The limited repertoire of antimicrobial agents targeted at protozoal parasites magnifies this challenge. Using Babesia caballi as both a model and a specific apicomplexan pathogen for which evidence of the elimination of transmission risk is required for international animal movement, we tested whether a high dose regimen of imidocarb dipropionate cleared infection from persistently infected asymptomatic horses and/or eliminated transmission risk. Clearance with elimination of transmission risk was supported by four specific lines of evidence: i) inability to detect parasites by quantitative PCR and nested PCR amplification; ii) conversion from seropositive to seronegative status; iii) inability to transmit infection by direct inoculation of blood into susceptible recipient horses; and iv) inability to transmit infection by ticks acquisition fed on the treated horses and then subsequently transmission fed on susceptible horses. In contrast, untreated horses remained infected and capable of transmitting B. caballi using the same criteria. These findings establish that imidocarb dipropionate treatment clears B. caballi infection with confirmation of lack of transmission risk either by direct blood transfer or a high tick burden. Importantly, the treated horses revert to seronegative status using the international standard for serologic testing and would permit movement between endemic and pathogen-free countries.