Oral Administration of Electron-Beam Inactivated Rhodococcus equi Failed to Protect Foals against Intrabronchial Infection with Live, Virulent R. equi

Abstract

There is currently no licensed vaccine that protects foals against Rhodococcus equi–induced pneumonia. Oral administration of live, virulent R. equi to neonatal foals has been demonstrated to protect against subsequent intrabronchial challenge with virulent R. equi. Electron beam (eBeam)-inactivated R. equi are structurally intact and have been demonstrated to be immunogenic when administered orally to neonatal foals. Thus, we investigated whether eBeam inactivated R. equi could protect foals against developing pneumonia after experimental infection with live, virulent R. equi. Foals (n = 8) were vaccinated by gavaging with eBeam-inactivated R. equi at ages 2, 7, and 14 days, or gavaged with equal volume of saline solution (n = 4), and subsequently infected intrabronchially with live, virulent R. equi at age 21 days. The proportion of vaccinated foals that developed pneumonia following challenge was similar among the vaccinated (7/8; 88%) and unvaccinated foals (3/4; 75%). This vaccination regimen did not appear to be strongly immunogenic in foals. Alternative dosing regimens or routes of administration need further investigation and may prove to be immunogenic and protective.

Antibody to Poly-N-acetyl glucosamine provides protection against intracellular pathogens: Mechanism of action and validation in horse foals challenged with Rhodococcus equi

“…equi pneumonia [ 8 , 9 ], it is generally felt that most attempts to date to create an effective R . equi vaccine have been unsuccessful [ 10 , 11 ]. There is no approved vaccine for R .…”

“…A final premise justifying immunizing pregnant mares to evaluate vaccine-induced immunity to R . equi is that foals are considered to be infected soon after birth [ 22 ] when they are more susceptible to infection [ 23 ] and when their immune system is less effective in responding to vaccines [ 10 , 24 – 26 ]. This precludes active immunization of very young foals as a strategy for vaccine evaluation against R .…”

In vitro evaluation of complement deposition and opsonophagocytic killing of Rhodococcus equi mediated by poly‐N‐acetyl glucosamine hyperimmune plasma compared to commercial plasma products

“…Immulon 4 HBX 96-well immunoassay plates (VWR International, Radnor, Pennsylvania) were coated with either the purified PNAG molecule 16 or whole R. equi. 4 For PNAG coating, plates were treated with 100 μL of PNAG, purified as described previously, 16 at 0.6 μg/mL and then incubated for a minimum of 3 hours. The strain of virulent R. equi used to coat plates (EIDL 5-331; confirmed virulent by polymerase chain reaction and in vivo infection 4,15 ) was grown overnight in brain heart infusion broth (BHIB; Becton, Dickinson, and Co, Sparks, Maryland) at 37 C; 100 μL of a bacterial suspension prepared at an optical density (OD) of 1 (corresponding to a concentration of 1.0 × 10 8 R. equi/mL or 2.5 mg/mL of R. equi antigen) 4 at a 650-nm wavelength was placed in sensitization buffer (0.04 M PO 4 [pH 7.2]).…”

“…2,3 Thus, there is a great need for prevention of R. equi pneumonia. No commercially available vaccines against R. equi exist, 1,4 such that prevention of pneumonia is based primarily on transfusion of plasma that is hyperimmune to R. equi (RE-HIP). 1,5,6 Transfusion of RE-HIP, however, is not completely effective in decreasing the incidence of R. equi pneumonia at horse breeding farms.…”

Antibody-based vaccine for tuberculosis: validation in horse foals challenged with the TB-related pathogen Rhodococcus equi

“…The sample size for the foal protection study was based on prior experience with 443 this model 6,30,48 indicating a dose of 10 6 CFU of R. equi delivered in half-portions to the 444 left and right lungs via intrabronchial instillation would cause disease in ~85% of foals. 445…”