Location: Animal Disease Research2011 Annual Report
1a. Objectives (from AD-416)
The objectives of this research are: (1) the testing of the hypothesis that tick antigens capable of inducing anti-tick immunity can be delivered through a transfected parasite; (2) discovery of new tick antigen vaccine targets; (3) an understanding of the vector competence of certain U. S. ticks for transmission of equine babesiosis, and (4) the determination if certain anti-babesial drugs are capable of clearing horses of persistent babesial infection.
1b. Approach (from AD-416)
The above objectives will be approached through the use of transfection to create replication competent parasites containing tick antigens known to induce anti-tick immunity. In parallel with this approach new tick antigens will be discovered and characterized through genetic approaches including suppressive subtractive hybridization and Serial Analysis of Gene Expression. New antigens will first be tested by subunit immunization for their ability to induce anti-tick immunity. Tick vectors present in the U. S. and known to feed on horses will be tested for their ability to transmit B. equi and/or B. caballi and finally selected chemotherapeutics will be tested for their ability to clear persistent B. equi and/or B. caballi infections. Clearance will be defined as the lack of detectable anti-parasite antibody, the lack of PCR detectable genetic elements of B. equi and/or B. caballi and finally by testing for the ability of know competent ticks to acquire infection from treated horses. Formerly 5348-32000-020-00D (12/06).
3. Progress Report
This research plan addressed critical gaps in our knowledge regarding transmissibility, pathogenesis, and treatment of tick-borne pathogens that affect cattle and horses. These tick-borne pathogens lead to significant production problems and barriers to trade for the United States livestock industry. The risk of outbreaks of bovine babesiosis due to increasing resistance of Rhipicephalus tick populations to acaricides in the U.S.-Mexico border and the risk establishment of endemic cycles of transmission of equine piroplasmosis following the recent outbreaks in the United States are the major issues of concern to the U.S. livestock industry. This report encompasses the progress of project plan 5348-32000-028-00D throughout FY06-FY11. Research accomplishments towards the control of bovine babesiosis and equine piroplasmosis include: 1) completion of the Babesia bovis genome sequence; 2) development of a stable Babesia bovis transfection system for more efficient delivery vaccine antigens; 3) demonstration of the transovarial transmission efficiency of B. bovis by Rhipicephalus microplus fed on persistently infected cattle; 4) completion of the Babesia equi genome sequence; 5) demonstration of the ability to eliminate Babesia caballi and B. equi infection through chemotherapeutic with imidocarb dipropionate; and 6) demonstration of the efficiency of species of ticks indigenous to the U.S.to acquire B. equi from infected horses and transmit to naïve horses. New project 5348-32000-034-00D to start 10-1-11.
1. Bovine babesiosis causes significant economic loss to the cattle industry worldwide. The emergence of Rhipicephalus microplus resistance to acaricides requires the development of novel methods to control this tick and thus the spread of the disease. Development of this novel live attenuated delivery system using vaccine components by ARS scientists in Pullman, WA, was done in collaboration with Washington State University scientists and is a significant advancement because it may only require one vaccination. The impact of this research is the provision of a B. bovis delivery vaccine system encoding vaccine components for controlling pathogen transmission and/or tick infestation.
2. Identified a new tick species. The discovery of ticks native to the United States with the capability of transmitting equine piroplasmosis has significantly increased the risk of transmission to the U.S. horse population. Furthermore, the potential of Rhipicephalus microplus to expand its geographic range in the U.S. due to acaricide resistance and increased abundance of wildlife hosts are additional risk factors. ARS scientists in Pullman, WA, identified species of ticks capable of transmitting Babesia equi in the Texas outbreak of this foreign animal disease, equine piroplasmosis. It was demonstrated that ticks present on the outbreak ranch in Texas are competent to transmit B. equi. Knowledge of which tick species are capable of transmitting this foreign parasite allows for risk assessment and derivation of control procedures.
3. Established protocols for treatment and elimination of Babesia equi infection. ARS scientists at Pullman, WA, demonstrated that B. equi infection can be eliminated from infected horses by treatment with anti-protozoan agent imidocarb dipropionate. Previously, euthanasia and permanent quarantine were the only options available for removal of the risk of transmission from asymptomatic carrier horses. This discovery gives USDA-APHIS and state veterinarians a tool for the elimination of the risk of transmission from asymptomatic carrier horses, thus controlling the outbreak of this foregin animal disease in the United States and will aid in returning the United States to infection free status.
Goff, W.L., Bastos, R.G., Brown, W.C., Johnson, W.C., Schneider, D.A. 2010. The bovine spleen: interactions among splenic cell populations in the innate immunologic control of hemoparasitic infections. Veterinary Immunology and Immunopathology. 138:1-14.