Vaccine Development for Prescottella Equi

Prescottella equi (formerly Rhodococcus equi) is an intracellular pathogen that causes pyogranulomatous pneumonia in Thoroughbred foals. There is currently no vaccine available for the prevention of this disease in foals despite years of research. Cell mediated immunity is considered crucial for overcoming an infection caused by this pathogen. The virulence associated protein (VapA) is a well characterized immunogenic protein associated with this pathogen and was used to develop DNA and recombinant protein vaccines in this study. Vaccine candidates and live P. equi based vaccine were tested in BALB/c mice. Mice were challenged with virulent P.equi 2 weeks following the last boost and IgG subtypes and bacterial clearance from spleen and liver determined. The DNA vaccine elicited a significant IgG2a response indicating a Th1 biased immune response. The IFN gamma response from DNA and recombinant VapA vaccinated mice was moderate. The results of the challenge study showed that neither the recombinant VapA protein nor DNA vaccine enhanced clearance of P. equi in this model.