Evaluation of equine immunoglobulin specific for Rhodococcus equi virulence-associated proteins A and C for use in protecting foals against Rhodococcus equi-induced pneumonia

Objective—To determine whether purified equine immunoglobulin specific for Rhodococcus equi virulence- associated proteins A and C (VapA and VapC) can confer passive protection against R equi-induced pneumonia in foals. Animals—Twenty-eight 3-week-old mixed-breed pony foals. Procedure—7 foals received IV injections of equine hyperimmune plasma (HIP) against whole-cell R equi, and 7 received purified equine immunoglobulin specific for VapA and VapC 1 day prior to intrabronchial infection with R equi strain 103+. Eleven foals were not treated prior to infection, and 3 control foals were neither treated nor infected. Heart rate, respiratory rate, and rectal temperature were recorded twice daily, and serum fibrinogen concentration and WBC count were determined every other day following infection. Foals were euthanatized 14 days following infection, and lung lesions and concentration of R equiin lungs were assessed. Results—The onset of clinical signs of pneumonia was significantly delayed in the HIP- and immu...