Rhodococcal Pneumonia in Horses

Key takeaways

Rhodococcal pneumonia is an infection of the lungs in horses. It is caused by the bacteria Rhodococcus equi, which is found in soil. 

  • Rhodococcal pneumonia is the most common cause of pneumonia in foals
  • In some cases, the infection can cause joint infection, diarrhea, and/or internal abscesses, whether pneumonia develops or not
  • The most common route of exposure is through inhalation of dust particles containing R. equi
  • Symptoms include coughing, difficulty breathing, fever, lethargy, and reduced appetite
  • Diagnostics include a complete physical evaluation, bloodwork, and diagnostic imaging
  • Specific tests such as PCR testing and collecting cell samples from the lungs are also required for definitive diagnosis
  • Treatment typically involves long-term antibiotic therapy and supportive care
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A closer look: Rhodococcal Pneumonia in Horses

Rhodococcal pneumonia can lead to an endemic infection in some breeding farms and which represents a significant economic weight on owners with respect to the liability of mortality, therapy, and surveillance programs.

Risk factors

Rhodococcal pneumonia commonly affects foals between 1 and 6 months of age and, in some cases, immunocompromised adult horses. It is a serious disease that might also lead to death. As such, symptoms of pneumonia in foals must be considered an immediate emergency.

In more severe cases, the infection can spread to other parts of the body.

Possible causes

R. equi is a bacterium commonly found in soil. The most common form of transmission in horses is through inhalation of dust particles containing the pathogen. Some farms are thought to be enzootic for R. equi, meaning the organism is commonly found in these farms, and foals born in these particular locations are more prone to develop rhodococcal pneumonia.

Main symptoms

Testing and diagnosis

The diagnostic process focuses on determining whether R. equi is the cause of pneumonia or not. Tests include a complete physical evaluation, bloodwork, diagnostic imaging such as ultrasound and X-rays, and specific testing to identify the bacteria such as PCR testing and collecting cell samples from the lungs through lavage.

Steps to Recovery

Treatment usually consists of long-term antibiotic therapy (up to 3-5 weeks).

Supportive therapy is also often necessary and involves ensuring the barn has good ventilation, that affected foals are in a relaxed environment, and tube feeding if the patients refuse to eat on their own.

With appropriate treatment, the survival rate is around 70 to 90%. Most foals fully recover if there are no complications such as antibiotic-induced enterocolitis.


Rhodococcal pneumonia is contagious and might result in endemic contagion between in-contact horses. Isolating affected foals is important in preventing contamination within the farm and in other foals. Prevention also includes monitoring for early signs of infection, frequently checking foals’ body temperature, and thorough cleaning of the foaling environment.

Is Rhodococcal Pneumonia in Horses common?

Rhodococcal pneumonia is particularly common in foals between 1 to 6 months of age. Sometimes, it also affects already immunocompromised adult horses. It is not the most common cause of pneumonia in foals, but is arguably the most serious.

Typical Treatment

  • Antibiotic therapy (3-5 weeks)
  • Supportive care
  • Hygienic practices

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