Experimental subacute foal pneumonia induced by aerosol administration of Corynebacterium equi.

This research investigates how subacute pyogranulomatous pneumonia was successfully induced in baby horses by repeatedly exposing them to air droplets containing Corynebacterium equi bacteria over seven days. Changes in their lung tissue, lymph nodes, and immune response matched symptoms seen in naturally occurring cases.

Experimental Method and Setup

• The researchers conducted an experiment to induce subacute pyogranulomatous pneumonia in three neonatal foals (baby horses).
• The process involves repeatedly exposing the subjects to aerosols containing the Corynebacterium equi bacteria for seven consecutive days.
• During each exposure, the foals were subjected to approximately 3.5 X 10(7) viable C equi, delivered in droplets tiny enough to penetrate the terminal airways.
• The control group consisted of three foals exposed to saline, instead of the bacteria-infused aerosols.

Results and Observations

• At the end of the experiment, clinical, pathological, and bacteriological symptoms presented in the three test subjects mirrored those displayed in foals with naturally occurring subacute C equi pneumonia.
• Radiographic imaging showed pronounced damage to the lungs before any clinical symptoms became observable.
• Cultures taken while the foals were still alive were inconsistent in identifying the presence of the C equi infection.
• In line with spontaneous cases of C equi pneumonia, the affected foals displayed lymphocytic hyperplasia (increased production of lymphocytes) in specific areas of the bronchial lymph nodes and spleen, and also developed granulomatous lesions in the lungs.
• These histological alterations indicate the stimulation of cell-mediated immune processes in foals infected with C equi.
• Lesions were confined to the lungs and the pulmonary lymph nodes, and post-mortem examinations revealed the presence of the C equi bacteria in the lung tissue of all three test subjects.
• Apart from the lungs, the C equi bacteria was also found in the trachea, mediastinal lymph nodes, mesenteric lymph nodes and caecal contents of one foal and in the liver of another.
• In contrast, the three control foals showed no evidence of pneumonia.

Conclusion and Implication

• The study successfully replicated subacute pyogranulomatous pneumonia in neonatal foals, using aerosol administration of Corynebacterium equi.
• The presence of activation of cell-mediated immune processes indicates that C equi bacteria might have the potential to trigger adaptive immunity in the host.
• The findings have clinical implications in diagnosing and identifying the early presence of C equi pneumonia, as the study demonstrated that radiographic evidence of pulmonary damage preceded the appearance of clinical signs, and pre-death cultures proved unreliable in identifying the infection.