Dissertation
EVALUATION OF THE EFFICACY OF IMIDOCARB DIPROPIONATE AGAINST THEILERIA HANEYI AND SUBSEQUENT ASSESSMENT OF VIRULENCE IN SPLENECTOMIZED HORSES
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2021
DOI:
https://doi.org/10.7273/000002455
Handle:
https://hdl.handle.net/2376/122104
Abstract
Identification of effective control strategies capable of successfully eliminating vector-borne pathogens are growing in demand as vector species previously constrained to certain regions of the world continue to slip into previously uninhabitable territories. With the development of a vaccine being an elusive reality for many veterinary pathogens, chemotherapeutics become the most viable control strategy for eradicating disease. Theileria haneyi is a recently identified causative agent of equine theileriosis that has been found in multiple Theileria equi-infected horses that failed to clear with multiple courses the gold standard for treatment, imidocarb diproprionate. With no known assessment of chemotherapeutic efficacy of any drug against T. haneyi, a primary objective was to then evaluate the effectiveness of imidocarb dipropionate.Additionally, with the global importance of recently discovered Theileria haneyi in equine health was recently shown by its resistance to elimination by imidocarb dipropionate (ID) and its interference in co-infected horses with ID clearance of Theileria equi infection. Genetic characterization of T. haneyi revealed marked genomic reduced compared to T. equi, and initial evaluation of infection dynamics have suggested reduced clinically severity in spleen-intact horses. Furthermore, splenectomized horses survive acute T. haneyi infection and progress to asymptomatic, persistent infection, which is in stark contrast to the fatal consequences of T. equi infection in splenectomized horses. This survival led to the hypothesis that T. haneyi is less virulent than T. equi. While progressive, invariably fatal disease was confirmed for T. equi infection of splenectomized horses in our previous dataset, seven of eight splenectomized, T. haneyi-infected horses survived. Further, in six horses co-infected with T. equi and T. haneyi, only horses cleared of T. equi infection by ID survived splenectomy and developed asymptomatic, persistent infections. The reduced virulence of T. haneyi compared to T. equi in splenectomized horses helps explain why T. haneyi was, until recently, undetected. This naturally occurring comparative reduction of virulence in a natural host provides a foundation for defining virulence mechanisms of theileriosis in the horse and apicomplexan in general.
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- Title
- EVALUATION OF THE EFFICACY OF IMIDOCARB DIPROPIONATE AGAINST THEILERIA HANEYI AND SUBSEQUENT ASSESSMENT OF VIRULENCE IN SPLENECTOMIZED HORSES
- Creators
- Kelly Sears
- Contributors
- Donald P Knowles (Advisor)Lindsay Fry (Committee Member)Jamie Kopper (Committee Member)Macarena Sanz (Committee Member)Robert Mealey (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Veterinary Medicine, College of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 83
- Identifiers
- 99900606855901842
- Language
- English
- Resource Type
- Dissertation