The Effectiveness of Anti-R. equiHyperimmune Plasma againstR. equiChallenge in Thoroughbred Arabian Foals of Mares Vaccinated withR. equiVaccine

Abstract

This study aimed to determine the effectiveness of a pregnant mare immunization of aRhodococcus equi(R. equi) vaccine candidate containing a water-based nanoparticle mineral oil adjuvanted (Montanide IMS 3012) inactive bacterin and virulence-associated protein A (VapA), as well as the administration of anti-R. equihyperimmune (HI) plasma againstR. equichallenge in the mares’ foals. The efficacy of passive immunizations (colostral passive immunity by mare vaccination and artificial passive immunity by HI plasma administration) was evaluated based on clinical signs, complete blood count, blood gas analysis, serological response (ELISA), interleukin-4 (IL-4) and interferon gamma (IFN-γ), total cell count of the bronchoalveolar lavage fluids (BALF) samples, reisolation rate ofR. equifrom BALF samples (CFU/mL), lung samples (CFU/gr), and lesion scores of the organs and tissue according to pathological findings after necropsy in the foals. The vaccination of pregnant mares and HI plasma administration in the foals reduced the severity ofR. equipneumonia and lesion scores of the organs and tissue by 3.54-fold compared to the control foals. This study thus indicates that immunization of pregnant mares withR. equivaccine candidate and administration of HI plasma in mares’ foals effectively protect foals againstR. equichallenge.