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

The research investigated if equine immunoglobulin specifically targeting Rhodococcus equi virulence-associated proteins A and C (VapA and VapC) could protect foals against pneumonia caused by R. equi. The study reveals that this targeted immunoglobulin provided a similar level of protection to the commercially available hyperimmune plasma (HIP), suggesting that immunoglobulin is a major protective component in HIP.

Methodology

• The study involved twenty-eight 3-week-old mixed-breed pony foals divided into four groups.
• One group received intravenous injections of equine hyperimmune plasma (HIP), which is traditionally used against whole-cell R. equi.
• Another group received purified equine immunoglobulin targeting VapA and VapC, proteins associated with the virulence of R. equi.
• The injections were given one day before the foals were infected with a strain of R. equi via their bronchial tubes.
• Eleven foals received no treatment before being subjected to the infection.
• The last group of three foals was the control group, which remained uninfected and untreated.
• Once the infection was established, researchers monitored the foals through daily measurements of heart rate, respiratory rate, rectal temperature while performing complete blood counts (including white blood cells) and fibrinogen concentration in the serum every other day.
• Fourteen days after infection, the foals were euthanized, and their lungs were assessed for lesions and for the concentration of R.equi.

Results of the Study

• The onset of pneumonia symptoms was significantly delayed in the foals that received HIP and the VapA and VapC-specific immunoglobulin.
• The lung lesions in the treated foals were less severe than those in the untreated group, and fewer R. equi organisms were cultured from the lungs of the treated animals.

Conclusions of the Study

• The research concludes that the purified immunoglobulin specifically targeting R. equi proteins — VapA and VapC — produced a similar degree of protection against R. equi-induced pneumonia as HIP.
• These findings suggest that the immunoglobulin is the primary component in HIP that confers protection against pneumonia caused by R. equi in foals.
• It also indicates that antibodies targeting R. equi’s VapA and VapC proteins have protective properties, providing a potential new avenue for preventive treatments.