Progress and obstacles in vaccine development for the ehrlichioses

Abstract

Ehrlichia are tick-borne obligately intracellular bacteria that cause significant diseases in veterinary natural hosts, including livestock and companion animals, and are now considered important zoonotic pathogens in humans. Vaccines are needed for these veterinary and zoonotic human pathogens, but many obstacles exist that have impeded their development. These obstacles include understanding genetic and antigenic variability, influence of the host on the pathogen phenotype and immunogenicity, identification of the ehrlichial antigens that stimulate protective immunity and those that elicit immunopathology, development of animal models that faithfully reflect the immune responses of the hosts and understanding molecular host–pathogen interactions involved in immune evasion or that may be blocked by the host immune response. We review the obstacles and progress in addressing barriers associated with vaccine development to protect livestock, companion animals and humans against these host defense-evasive and cell function-manipulative, vector-transmitted pathogens.

Keywords::

• antibody epitope
• antigenic variation
• Ehrlichia
• immune evasion
• immunopathology
• immunoprotection
• tick
• vaccine
• zoonosis

Acknowledgements

This manuscript summarizes the information provided by many investigators covering decades of scientific inquiry. Although all relevant scientific discoveries were not cited in this article, due to the limited space available, we dedicate this article to all the investigators who have made important contributions towards the development of vaccines for the ehrlichioses.

Financial & competing interests disclosure

Jere W McBride and David H Walker are supported by grants (AI0071145 and AI069270 to Jere W McBride; AI 31431–18 to David H Walker) from the National Institutes of Health (NIH) and jointly by the Clayton Foundation for Research. Jere McBride and David Walker have independent and joint intellectual property related to vaccines and diagnostics for the ehrlichioses. Jere McBride has received prior research funding from Merial Limited. This entity did not provide support for the current manuscript. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.