Most of the foals born in Texas are usually born in the spring.  The hot dry weather we usually have in August increases the chance of a severe type of pneumonia in foals called Rhodococcus equi pneumonia.  Although almost all horse farms have some amount of this organism on the premises, the disease is common and severe on some farms, sporadic on others, and fortunately unrecognized on most. 

The organism is naturally present in the intestinal tract of foals up to 3 months of age and their feces are a source of infection.  With high summer temperatures, the organism can multiply 10,000 fold in only 2 weeks.  Ingestion and inhalation are the 2 main sources of infection.  The most common symptom of the infection is a chronic suppurative bronchopneumonia with abscesses developing in the lung. 

In contrast to most cases of pneumonia where the foals are sick fairly acutely and diagnosis and treatment can begin immediately, Rhodococcus pneumonia is characterized by a slow progressive onset.  Because of this, many foals are able to compensate for the loss of lung function until they are severely ill.  Once severely ill, treatment is difficult and many foals do not survive.  Early clinical signs include a mild fever and a slight increase in respiratory rate.  As the disease progresses, the foals become lethargic, appetite decreases, and they have labored and rapid breathing.  A cough and nasal discharge are usually not seen as they are with other pneumonias.  Rarely, foals can develop a subacute form of the disease and are found in severe respiratory distress or already dead.  Rhodococcus can also cause intestinal signs in foals such as colic, weight loss, and diarrhea.  Joint problems can also develop either from immune mediated causes or from actual infection of the joints with the organism.  Our next program will deal with the diagnosis and treatment of this infection.