Differential expression of the rhoptry associated protein -1a in Theileria equi; Implications for host cell invasion

Primary Author: Cynthia Onzere

Faculty Sponsor: Carlos Suarez


Primary College/Unit: College of Veterinary Medicine

Category: Medical and Life Sciences

Campus: Pullman




Principal Topic

Theileria equi (T. equi) is one of the causative agents of equine piroplasmosis, a severe tick-transmitted disease that affects all equid species. Presently, there is no vaccine for the control of the parasite. T. equi is an Apicomplexan organism characterized by the presence of secretory organelles, such as the rhoptries, on the anterior end that are essential for invasion and establishment of the parasite within the host cell. Rhoptry proteins have been shown to be important in the attachment of several apicomplexan parasites to the host cell during invasion. Despite their functional importance, the pattern of expression and potential of rhoptry proteins as vaccine targets in T. equi remain unexplored.


We evaluated the expression of a putative T. equi rhoptry protein known as the rhoptry associated protein-1a (RAP-1a) in the parasite’s invasive stages in horses. RAP-1a was selected because it is widely conserved among the closely related Babesia and Theileria parasites.


Our findings indicate that RAP-1a is expressed in the merozoite stage of development that invades red blood cells (erythrocytes) but it’s not expressed in the sporozoite stage that invades peripheral blood mononuclear cells. This indicates that T. equi RAP-1a could be important for invasion of erythrocytes and could therefore be a marker for pathogenicity because the symptomatic stage of T. equi infection is associated with the intra-erythrocytic stage of the parasite’s development. Future work will be focused on defining the functional relevance of RAP-1a in T. equi and its role in eliciting protective immune responses.