Comparison of tracheal aspiration with other tests for diagnosis of Rhodococcus equi pneumonia in foals.

This research evaluates tracheal aspiration’s effectiveness in diagnosing Rhodococcus equi pneumonia in foals. It found that aspiration, coupled with bacterial isolation, was the most valuable method, surpassing radiography, serodiagnosis, and fecal culture in accuracy.

Methodology

The study made use of an experimental model of Rhodococcus equi pneumonia in foals. This was achieved by:

• Inducing pneumonia in the foals by spraying a virulent R. equi strain (ATCC 33701) into their trachea.
• Multiple diagnostic tests, including tracheal aspiration, radiography, serodiagnosis, and fecal culture, were carried out to determine the presence of R. equi pneumonia.

Findings

Here are the significant findings from the research:

• The foals developed a fever 11 to 16 days after the bacterial inoculation.
• A continual isolation of R. equi was observed from tracheal aspirates collected through a transnasal silicone catheter, from day 8 to day 32 post-inoculation.
• Radiography, serodiagnosis, and fecal culture were valuable diagnostic methods, but their effectiveness was limited compared to tracheal aspiration.

Additional Diagnostic Techniques

In addition to the primary diagnostic tests, the researchers also used two rapid diagnostic techniques:

• The indirect fluorescent antibody technique (IFA), which uses a monoclonal antibody against the 15- to 17-kDa virulence-associated antigens (VapA) of R. equi.
• A Polymerase Chain Reaction (PCR) targeting the structural gene of VapA.

These methods were found to be less sensitive than the isolation technique in detecting bacteria in tracheal aspirates.

Conclusion

From the study, the researchers concluded that a combination of tracheal aspiration and bacterial isolation is the most valuable method for routine diagnosis of R. equi pneumonia in foals. This approach proved to be more accurate than other tested methods such as radiography, serodiagnosis, and fecal culture.