Location: Animal Diseases Research
2013 Annual Report
Sub-objective 1A: Identify surface exposed antigens expressed by Babesia bovis during its development within the tick.
Sub-objective 1B: Test if antibody response in cattle immunized with tick midgut surface antigens enhances access of bovine antibodies to tick hemolymph.
Sub-objective 1C: Determine if immunization with Babesia tick stage and midgut antigens blocks B. bovis transmission.
Objective 2: Evaluate the risks of B. equi or B. caballi transmission by species of ticks indigenous to the United States.
Sub-objective 2A: Identify tick species feeding on horses at the outbreak ranch in Texas that are capable of transmitting B. equi.
Sub-objective 2B: Determine the B. equi transmission efficiency of vector-competent tick species from the outbreak ranch in Texas.
Objective 3: Determine the impact of both new and current chemotherapeutic agents on the clearance of B. equi or B. caballi from persistently infected horses and on the risks of transmission.
Sub-objective 3A: Assess the efficacy of imidocarb dipropionate to eliminate B. equi infection
Sub-objective 3B: Develop a serological method that rapidly and accurately predicts elimination of B. equi infection following treatment.
Sub-objective 3C: Assess tick-borne transmission risk of imidocarb dipropionate treated horses.
In contrast to bovine babesiosis, the control strategy for equine babesiosis is based on serological restriction of infected horses from entering the country. Due to previous use of the complement fixation test (CFT), which lacked sensitivity, infected horses have been admitted into the U.S. which likely led, at least in part, to the recent reemergence of this foreign equine disease in the U.S. The goal of this research plan related to equine babesiosis is to assist the Animal Plant Health Inspection Service (APHIS), State Veterinarians and owners in eliminating Babesia infections, transmission risk, and potential endemicity by developing pharmacological interventions. Replacing 5348-32000-028-00D (October 2011).
We have continued to develop the Babesia transfection system that can be used for development of live attenuated vaccine strains that deliver vaccine antigens, or can be used as a system to knockout specific genes for studies of gene function and strain attenuation. Progress includes development of a new transfection vector that can express two different exogenous genes at the same time. This system was used to transfect an attenuated strain of B. bovis and the transfected strain remained stable in infected cattle. Cattle infected with this transfected strain were protected from disease when challenged with a virulent strain of B. bovis, demonstrating that transfected attenuated strains can be used as live vaccines to protect against B. bovis infection (Objective 1).
As part of our ongoing work on Babesia (Theileria) equi, we have determined that imidocarb dipropionate can eliminate Babesia equi from naturally persistently infected horses and we have shown that this treatment can remove the future risk of transmission (objective 3a). Because many infected animals that have been cleared remain seropositive on the commercially available regulatory approved cELISA assay we have also begun to identify other immunological markers that may be more useful for defining clearance of infection. We have done this by beginning to characterize the full repertoire of immunoreactive antigens in T. equi infected and treated/cleared horses (Objective 3b). Also, as part of our cooperative agreement between Texas A&M University and our laboratories we have identified tick species feeding on horses in the Equine piroplasmosis outbreak area of Texas and have begun vector competence studies to determine which of these species are capable of transmitting equine piroplasmosis (Objective 2).
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.
Kappmeyer, L.S., Thiagarajan, M., Herndon, D.R., Ramsay, J.D., Caler, E., Djikeng, A., Gillespie, J.J., Lau, A.O., Roalson, E.H., Silva, J.C. 2012. Comparative genomic analysis and phylogenetic position of Theileria equi. Biomed Central (BMC) Genomics. BMC Genomics 2012, 13:603.
Ueti, M.W., Mealey, R.H., Kappmeyer, L.S., White, S.N., Kumpula-Mcwhirter, N., Pelzel, A.M., Grause, J.F., Bunn, T.O., Schwartz, A., Traub-Dargatz, J.L. 2012. Re-emergence of the apicomplexan theileria equi in the United States: Elimination of persistent infection and transmission risk. PloSONE 7(9):e44713.
Gomes Da Silva, M., Domingos, A., Esteves, M.A., Antunes, S., Cruz, M.M., Suarez, C.E. 2013. Evaluation of the growth-inhibitory effect of trifluralin analogues on in vitro cultured babesia bovis parasites. International Journal for Parasitology. (3):59-68.
Hall, C.M., Busch, J.D., Palma-Cagle, K.A., Scoles, G.A., Ueti, M.W., Kappmeyer, L.S., Wagner, D.M. 2013. Genetic characterization of theileria equi infecting horses in North America: evidence for a limited source of U.S. introductions. International Journal for Parasitology. doi:10.1186/PV.1756-3305-6-35.
Gomes Da Silva, M., Graca, T., Suarez, C.E., Knowles Jr, D.P. 2013. Repertoire of theileria equi antigens bound by equine antibody during persistent phase of infection. Molecular and Biochemical Parasitology. 188(2):109-115.
Baptista, C., Lopes, M.S., Tavares, A.C., Rojer, H., Kappmeyer, L.S., Mendonça, D., Da Câmara Machado, A. 2013. Diagnosis of theileria equi infections in horses in the Azores using cELISA and nested PCR. Ticks and Tick Borne Diseases. 4(3):242-245.