ARS | Publication request: In vitro activity of ponazuril against Theileria equi

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 27, 2011
Publication Date: April 30, 2012
Repository URL: http://dx.doi.org/10.1016/j.vetpar.2011.10.036
Citation: Wise, L.N., Ueti, M.W., Kappmeyer, L.S., Hines, M.T., White, S.N., Davis, W., Knowles Jr, D.P. 2012. In vitro activity of ponazuril against Theileria equi. Veterinary Parasitology. 185(2-4):282-5.

Interpretive Summary: Two parasites, Babesia equi and Babesia caballi cause the disease piroplasmosis in horses. Babesia equi enters the horse’s bloodstream after being bitten by certain ticks or by other methods of blood transfer. Infection can be fatal or the horses recover and develop a lifelong infection and are a source of transmission to uninfected horses. To date, no drug has been shown to completely eliminate infection. The drug ponazuril, which is marketed as an oral paste under the name Marquis® (Bayer Animal Health), is used in equine medicine as an effective treatment for equine protozoal myeloencephalitis (EPM). This drug is also effective against several other animal parasites. In an attempt to find a drug that can eliminate Babesia equi infection, we tested the ability of ponazuril to inhibit this parasite’s growth in cell culture. Our results indicate that at high concentrations, ponazuril can completely inhibit the growth of Babesia equi. Further testing is warranted to assess its activity in treatment of infected horses.

Technical Abstract: The equid hemoprotozoan parasite Theileria equi is endemic in most regions worldwide. Infection of horses is a cause of significant economic loss due to costs associated with disease and restriction of trade with non-endemic nations. The ability of certain drugs such as imidocarb dipropionate to eliminate persistent T. equi infection and transmission risk is controversial. The anti-protozoal agent ponazuril has been used successfully to treat equine Sarcosystis neurona and Toxoplasma gondii. The hypothesis that ponazuril inhibits replication of T. equi in vitro was tested. Theileria equi infected equine erythrocyte cultures were treated with ponazuril at multiple concentrations. Cessation of parasite replication was observed over a 5 day period and the degree of inhibition was variable between drug concentrations. Ponazuril inhibited T. equi in erythrocyte culture at all concentrations tested but parasite elimination required at least 500µg/mL. The high dose of ponazuril required for in vitro inhibition likely limits its ability to control or clear T. equi infection in vivo, however additional research to evaluate related drugs is warranted.