R. Equi and Foal Pneumonia D.P. Leadon and M. Klay

Rhodococcus equi is primarily an important cause of broncho-pneumonia and abscess formation in foals aged > 6 months although a minority of cases first present at 8 months postpartum and the disease is now seen occasionally in adult horses.

Although R. equi infection is usually a respiratory disease, abscessation can occur in extra-pulmonary sites. Per-acute onset, often totally unresponsive to therapy, is also seen. In the classical form, the disease is manifest as an ill-thrift, accompanied by high fever, profound neutrophilia and muco-purulent respiratory discharge which when disturbed by inhalation and expiration gave rise to the colloquial term “Rattles”. Inappetence was seldom seen even in terminally ill foals, which often maintained a good appetite until moribund.

This comparatively readily diagnosed, classical form is now seldom seen in our experience. Heightened awareness, the need to minimise lost productivity due to ill-thrift and wasteful / inappropriate medication, the high cost of often protracted periods of treatment with macrolide antibiotics and rifampin, together with the dangers of antibiotic resistance and the risks of adverse drug reactions in the foal have all resulted in greater efforts at achieving earlier, accurate diagnosis and improved medication.

Fever is now seldom seen in these “sub-clinical” cases. Laboratory findings often, but not always include a mild neutrophilic leucocytosis (>14,000x109/l), hyperfibrinogenaemia and in our experience, microcytic RBC manifest as reduced MCV, depending on the stage of disease. Radiology is seldom used in clinical practice and the significance of R. equi serology is controversial and not readily available. Capture of exhaled breath for culture and PCR using impaction samplers is currently under evaluation. Thoracic ultrasonography may demonstrate abscessation or potentially pre-cursor change. These findings have been used as a basis for the justification of recovery of respiratory tract secretions for cytology and culture and where available, for PCR.  [...]