Rhodococcus Pneumonia in a Foal

History

“Lizzy”, a 2 month old Arabian filly presented to SWEH for evaluation of a sudden onset of fever, respiratory distress, and diarrhea.  Approximately one month previously, she had been shipped from Tucson to Phoenix for her dam to be bred.   She was treated on the breeding farm with intravenous fluids, antibiotics, and Biosponge for one day with no improvement so she was transported to SWEH for further evaluation and treatment.

Upon presentation, “Lizzy” was dull, depressed and lethargic. She was breathing very fast and with increased effort, and she would cough when she walked. She had nasal discharge and her lung sounds were very harsh and wet with wheezes heard on auscultation.  She had a febrile and appeared dehydrated. She had projectile watery diarrhea. She had excess fluid (effusion) in both stifles, but was not lame at a walk. 

The following diagnostics were performed:

A) This radiograph of Lizzy’s lungs shows multiple pulmonary abscesses caused by R. equi

B) This radiograph shows normal lungs in a similar aged foal.

C) This thoracic ultrasound image shows a cavitating lesion (abscess) caused by equi

D) Bilateral stifle synovitis (non-septic inflammation of the joint)

Diagnosis: Rhodococcus equi pneumonia, diarrhea, and synovitis

Treatment:

“Lizzy” was placed on specific antibiotics (clarithromycin and rifampin) that are able to penetrate abscesses, enter the cells, and kill R. equi.  Intravenous fluids were given to maintain hydration and replace fluid losses from her diarrhea.  Biosponge and metronidazole were added to absorb toxins and treat other bacterial causes of diarrhea (such as Clostridium).  The diarrhea resolved within a few days of treatment.  Blood work was repeated and revealed an increased white blood cell count and a very high platelet count.  Since “Lizzy” was stressed from her illness and was grinding her teeth (which may be a sign of gastric ulcers), she was placed on sucralfate and Gastrogard to treat and prevent gastric ulcers.  “Lizzy” continued to have an increased respiratory rate and effort and required intranasal oxygen therapy and bronchodilators to help open up her airways.  She had high fevers which were treated with anti-inflammatory medications and alcohol baths.  While in the hospital, Felizshah was very ill; she had a poor appetite and was losing weight.  She was offered a variety of feeds and supplemented with corn oil to help add calories to her diet.  She also received B vitamins to help stimulate her appetite.  “Lizzy” was very sick and was in the hospital for nearly 3 weeks. At the time of discharge she was eating and breathing much better, but still had abnormal lung sounds. The swelling in her stifle joints had nearly resolved and her diarrhea was completely resolved.

Follow Up:

“Lizzy”  continued to improve with antibiotic treatment at home.  She returned 6 weeks later for a check up (after 9 weeks of treatment). Her respiratory rate and effort were normal and no crackles or wheezes were heard in her lungs.  Her white blood cell count, platelet count, and fibrinogen had returned to normal values.  Ultrasound of her chest showed only some minor areas of non-aerated lung (consolidation).   No abscesses were visualized. Her antibiotics were discontinued and she did very well post-treatment… back to being a normal healthy foal.

EDUCATION:

Rhodococcus equi is a widespread bacterium that lives in the soil.  It grows very well in horse manure and thus may become endemic on some breeding farms.   It is an important cause of disease in foals aged 1- 5 months.  Rhodococcus is an intracellular bacterium which can replicate in the intestine of foals up to about 3 months of age. Most foals are thought to be infected during the first 2 weeks of life when they are most susceptible.  However, clinical signs may not develop until months later.  

Inhalation of contaminated dust particles is the most important route leading to infection of alveolar macrophages.  This causes multiple abscesses to form in the lungs resulting in pneumonia.  It can also infect the gastrointestinal tract leading to colic or diarrhea.  Clinical signs of Rhodococcus infection can include fever, increased respiratory rate and effort, coughing, bilateral nasal discharge, diarrhea, synovitis (inflammation of joints), uveitis (inflammation of the eye).  Most affected foals have an increased white blood cell count and fibrinogen (a marker of inflammation).  Bacteremic spread from the lungs or gastrointestinal tract may sometimes result in infection of the bones, joints, or abscess formation in other parts of the body, including the spinal cord.  Most foals with Rhodococcus recover fully with appropriate treatment, but Rhodococcus may be fatal, especially if it spreads to joints or bones.

Prevention of Rhodococcus Equi pneumonia in Foals:

• Ensure adequate colostrum intake and check IgG 
• Take temperature and auscult lungs often in young foals
• House foals in well ventilated areas 
• Remove feces from stalls and paddocks frequently
• Decrease dust formation in stalls and paddocks
• Isolate sick foals
• On farms with enzootic R. equi problems, hyperimmune plasma may be administered during the first week of life.

Take home message: Even when detected early (this filly was hospitalized within 24hrs of showing signs of illness), Rhodococcus can take a long time to resolve with appropriate treatment.  The prognosis for full recovery is generally quite good when treated promptly, aggressively and appropriately.