Research Project
9998279
PROJECT SUMMARY: Tick-transmitted rickettsial diseases of the genera Anaplasma, Ehrlichia, and Rickettsia remain a growing public health concern in the USA and many parts of the world. The diseases include one of the oldest known rickettsial diseases, Rocky Mountain spotted fever (RMSF) caused by Rickettsia rickettsii. RMSF remains a serious disease of people and continues to be a public health concern in the USA and several North, Central and South American countries. Clinical signs of RMSF include fever, headache, nausea, vomiting, muscle pain, lack of appetite, and rash. The disease can progress rapidly to a life-threatening illness in untreated patients, resulting in high mortality rates ranging from 30-80%. During the last two decades, reported RMSF cases continue rising in parts of North America. Tick-borne diseases (TBDs) require the interplay of humans, ticks and reservoir animal hosts. We believe that developing a vaccine to prevent the disease can be accomplished by engaging in collaborative research with a team of experts having diverse expertise and yet having common broad research interests. Since dogs develop disease similar to people, a vaccine to prevent the disease in this host will most likely be effective in controlling the disease spread from wildlife, ticks and also infections from dogs to people. We recently tested two experimental vaccines; a subunit vaccine, which included two R. rickettsii recombinant proteins (RCA) and a whole cell inactivated antigen vaccine (WCA), to confer protection against virulent R. rickettsii infection challenge. WCA offered complete protection against RMSF, while RCA did not. This prior published work offers a strong scientific premise for the proposed detailed investigation. In particular, we aim to further characterize WCA in determining A) the duration of protection, B) the role of adjuvants in defining protection, C) the type of immune response observed, and D) the protection against tick transmitted homologous and heterologous challenges. We believe that this project, supported by strong scientific premise, addresses a significant public health problem. The goals are innovative as we will be the first group to investigate RMSF vaccine development using a physiologically relevant animal- tick-pathogen infection model. The central hypothesis of our application is that WCA protects against lethal RMSF caused by blood- and tick-borne infections, resulting from geographically distant pathogen strains, by stimulating immune protection for one year or longer. The specific aims of this application are: 1) Evaluate inactivation methods for preparing WCA and adjuvants in defining the vaccine protection. 2) Evaluate WCA protection against tick-transmitted challenges. 3) Evaluate WCA protection against R. rickettsii heterologous strain infection challenges. At the conclusion of this project, we expect that our efforts will translate to a fully developed vaccine, which is efficacious in an animal model known to naturally acquire R. rickettsii infections from an infected tick leading to life-threatening RMSF. We believe that achieving goals of this application will pave the way for extending vaccine studies to protect people from this lethal disease in the very near future.
