Rhodococcus Equi

Question 1

What is the most common cause of pneumonia in foals? How do they typically become infected?

Answer 1

Rhodococcus equi - Gram-negative facultative intracellular coccobacillus

common environmental pathogen especially in large equine breeding operations and is readily aerosolized during dry and dusty periods –> NOT a normal inhabitant of equine respiratory tract

Question 2

What horses are most commonly affected by Rhodococcus equi pneumonia? What is its pathogenesis?

Answer 2

foals 1-6 months old –> any earlier = maternal antibodies

organism is inhaled and subsequently invades alveolar macrophages where it replicates, producing pyogranulomatous pneumonia and pulmonary abscessation

Question 3

Other than the lungs, what body system is also commonly affected my Rhodococcus equi?

Answer 3

GIT –> some foals develop ulcerative colitis and mesenteric lymphadenitis which manifest as diarrhea or colic

Question 4

What clinical signs are associated with Rhodococcus equi infection in foals? What are 2 common clinicopathologic abnormalities?

Answer 4

• intermittent fever
• inappetence and weight loss/failure to gain weight
• cough, tachypnea, increased respiratory effort (nostril flaring)
• abnormal thoracic auscultation - wheezes, crackles
• nasal discharge

neutrophilic leukocytosis + hyperfibrinogenemia

Question 5

What are 2 diagnostics used for confirmation of Rhodococcus equi infection?

Answer 5

1. thoracic U/S - pulmonary abscessation
2. transtracheal wash and positive culture

Question 6

What is commonly seen on thoracic radiographs in cases of Rhodococcus equi pneumonia?

Answer 6

numerous radiodense abscesses distributed throughout the lung fields

Question 7

What is used to treat Rhodococcus equi pneumonia? What 4 methods of supportive care is commonly included?

Answer 7

Rifampin + Erythromycin/Clarithromycin/Azithromycin

1. anti-inflammatory
2. cool temperature-controlled environment
3. intranasal oxygen supplementation
4. hydration

Question 8

What are 4 possible complications associated with Rhodococcus equi pneumonia?

Answer 8

1. internal abscessation - ulcerative colitis, intervertebral abscess cause neurologic deficits caudal to the lesion
2. septic arthritis
3. osteomyelitis
4. joint effusion (non-septic)

Question 9

What is prognosis of Rhodococcus equi pneumonia like?

Answer 9

fair to good as long as appropriate therapy is instituted as soon as the disease is recognized

• because of the slow and insidious nature of the disease, some foals do not get examined and treated until the disease is severe = worse prognosis

Question 10

What are 2 ways of preventing Rhodococcus equi pneumonia in equine breeding facilities? What is no longer recommended?

Answer 10

1. administration of hyperimmunized plasma against R. equi early in life
2. maintain strict environmental cleanliness and reduce dusty environments

prophylactic administration of macrolides –> antibiotic resistance + questionable efficacy

Question 11

What are 3 methods for early detection of Rhodococcus equi pneumonia at equine breeding facilities?

Answer 11

1. routine measurement of body temperature and respiratory rate in age susceptible foals (1-6 months)
2. routine screening of a CBC observing for leukocytosis, serum amyloid, and/or hyperfibrinogenemia
3. routine diagnostic screening of lung via U/S or radiography