Rhodococcus equi (Prescottella equi)vaccines; the future of vaccine development

Abstract

For decades researchers have been targeting prevention of Rhodococcus equi (Rhodococcus hoagui/Prescottella equi) by vaccination and the horse breeding industry has supported the ongoing efforts by researchers to develop a safe and cost effective vaccine to prevent disease in foals. Traditional vaccines including live, killed and attenuated (physical and chemical) vaccines have proved to be ineffective and more modern molecular-based vaccines including the DNA plasmid, genetically attenuated and subunit vaccines have provided inadequate protection of foals. Newer, bacterial vector vaccines have recently shown promise for R. equi in the mouse model. This article describes the findings of key research in R. equi vaccine development and looks at alternative methods that may potentially be utilised.

Rhodococcus equi Joint Sepsis and Osteomyelitis Is Associated With a Grave Prognosis in Foals

“…Future treatments may include novel antimicrobials or non-traditional delivery modalities, such as liposomal formulations of gentamicin (5). Preventative approaches for decreasing the prevalence of endemic R. equi should be a continued priority, including research into vaccinations (20). In the meantime, the use of prophylactic antibiotics needs to be weighed against the increase in resistance (12).…”

The extracellular thioredoxin Etrx3 is required for macrophage infection in Rhodococcus equi

“…The rise of multidrug-resistant R. equi strains is making current antibiotherapies ineffective [3,4]. In addition, any attempts to develop a vaccine against R. equi have been unsuccessful so far [5]. Because of this, hyperimmune plasma administration has been implemented as a preventative primary intervention in foals, despite of its high costs and variable efficacy [6].…”

“…However, the essential role of this extracellular thioredoxin during macrophage infection makes the etrx3-null mutant strain an attractive candidate for the development of an attenuated vaccine. The Δetrx3 deletion strain might be able to elicit a strong immune response against R. equi since it was unable to survive phagocytosis despite of carrying a functional pVAPA virulence plasmid, which is required to generate both cell-mediated and humoral immune responses [5].…”

A Novel Screening Strategy Reveals ROS-Generating Antimicrobials That Act Synergistically against the Intracellular Veterinary Pathogen Rhodococcus equi

“…During the last decade, the number of R. equi isolates resistant to commonly used antimicrobials has dramatically increased [7][8][9], making current antibiotherapies often ineffective [10]. Primary preventative strategies based on the use of vaccines or hyperimmune plasma administration do not confer full protection against this pathogen [11][12][13]. Thus, new treatments based on a combination of clinically established antimicrobials with novel anti-R. equi compounds could be the only realistic option to solve in the short term the crisis caused by antimicrobial resistant strains.…”