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ARS Home » Research » Research Project #440740

Research Project: Building Foundations for E. Ruminantium Vaccine Development

Location: Operations

Project Number: 3022-32000-012-007-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 1, 2021
End Date: Aug 31, 2023

Objective:
Major knowledge gaps slow progress developing interventions against heartwater, which is caused by the obligate intracellular bacteria, Ehrlichia ruminantium. This work is designed to start to address some of these gaps. Amblyomma maculatum would be the likely tick vector for E. ruminantium, should this pathogen be introduced into the U.S. The capacity of A. maculatum to transmit E. ruminantium is well demonstrated. However, transmission models required for vaccine development using this tick have not been established. Based on field challenges conducted in South Africa it is likely that tick transmission has increased virulence as compared to needle inoculation. Additionally, large knowledge gaps remain in the understanding of the pathophysiology of heartwater, which is likely due to immune dysregulation. Finally, the need for live animals or cell culture to grow E. ruminantium limits the ability to produce an inactivated vaccine. The major objectives of this work are to: 1) Determine if tick feeding and salivary glands will enhance virulence of E. ruminantium. 2) Characterize the anti-E. ruminantium immune response that associates with mild disease and/or immune protection. 3) Work toward developing a cell free culture system for E. ruminantium. 4) Develop collaboration with scientists at CIRAD and CaribVET housed in Guadeloupe in support of determining the risk of regional spread of E. ruminantium and A. variegatum ticks. The planned research will be used to train a graduate student in developing expertise in tick-borne diseases. The student will be broadly trained in research involving bacterial cell culture, animal infection studies, molecular biology, host response assessment, field studies involving tick collections, tick rearing and manipulations, and tick-host-pathogen interactions.

Approach:
For Objective 1, Amblyomma maculatum ticks will be infected with E. ruminantium via inoculation or acquisition feeding to determine infection rates and levels. Disease severity will then be compared between groups of animals infected via tick feeding or IV inoculation. In Objective 2, the anti- E. ruminantium immune response will be measured using a variety of approaches including PBMC stimulation assays, cytokine/chemokine magnetic bead multiplex assays and/or RNAseq to measure the TH1, TH2 and TH17 cytokine responses to E. ruminantium through time. For Objective 3, the initial steps of developing a cell free culture system will involve optimization of purification and cell free storage of E. ruminantium and validation of methods to measure protein incorporation that do not require radioactive materials.