Effect of hyperimmune plasma on the severity of pneumonia caused by Rhodococcus equi in experimentally infected foals.

The research investigates the effect of using hyperimmune plasma (HIP), derived from R. equi immune horses, on the severity of R. equi-induced pneumonia in newborn horses. The main finding is that, although all foals developed signs of respiratory disease, administration of HIP decreased the severity of lung lesions seen in radiographs and delayed time to increased respiratory effort.

Objective of the Research

The core objective of the study was to assess the potential of hyperimmune plasma (HIP) – in this case collected from horses immunized against Rhodococcus equi – as a prophylactic measure against pneumonia induced by the same bacterium. This was measured in foals that were administered with either HIP or a control substance (saline) and then infected with R. equi.

Research Methodology

• The researchers worked with a sample of 30 newborn foals which were divided into two groups.
• One group received R. equi HIP while the other was administered saline, both at two days of age.
• At seven days of age, all foals were infected with a potent strain of R. equi to induce respiratory disease.

Research Findings

• All foals, both in the HIP and control groups, developed signs of respiratory disease.
• However, radiographic scores on day 28 after infection were significantly higher in control foals, indicating a greater severity of lung lesions.
• Moreover, neutrophil (a type of white blood cell that fights infection) concentrations on day 49 were significantly higher in control foals, suggesting a more severe immune response in those animals.
• The time to reach a respiratory effort score of 2 or higher (indicating more severe disease) was significantly shorter in control foals compared to those who received HIP.
• There was no significant difference in mortality between the two groups. Three foals died or were euthanized before the conclusion of the study, and all were from the group treated with HIP.
• Finally, the concentrations of VapA (a virulence-associated protein of R. equi) were significantly higher in the group who received the HIP treatment.

Conclusion

The study concluded that administration of R. equi HIP mitigates the severity of R. equi-induced pneumonia cases, as evidenced by less serious radiographic lesions and a delayed onset of severe respiratory disease. However, the treatment didn’t significantly affect mortality rates.