rhodococcus equi in foals
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Rhodococcus equi in foals. James Montgomery, DVM September 8, 2008. Rhodococcus equi. Gram-positive aerobic rod Facultative intracellular pathogen Helps it hide from the immune system Foals have an immature immune system Opportunistic pathogen in immunocompromised humans - HIV. - PowerPoint PPT PresentationTRANSCRIPT
James Montgomery, DVMSeptember 8, 2008
Gram-positive aerobic rod
Facultative intracellular pathogen• Helps it hide from the
immune system• Foals have an immature
immune system Opportunistic
pathogen in immunocompromised humans - HIV http://www.cvm.tamu.edu/acvp/Rhodococcus/Rhodococcus.htm
Saprophytic inhabitant of soil Widespread in the environment of
most horse farms Clinical disease ranges from
unrecognized or sporadic on some farms to enzootic and devastating on others• Morbidity rates as high as 40%
Methods for control and prevention not well understood
No effective vaccines available presently
Administration of R. equi hyperimmune plasma has been shown to be effective prophylactically
Foals between 3 weeks and 5 months of age
http://www.ca.uky.edu/gluck/ResearchDVS.asp
Most common: chronic suppurative bronchopneumonia with extensive abscessation• Early clinical diagnosis difficult – slow progression
and foals able to compensate well
Early clinical signs: • Mild fever• Slight increase in respiratory rate
With progression:• Decreased appetite, lethargy, fever, tachypnea, and
labored breathing (nostril flaring, and increased abdominal effort)
Inhalation is major route of pneumonic infection
Incubation period• Experimentally: 9 days with heavy inoculum
to approximately 2 to 4 weeks when lower inoculum administered
CBC, fibrinogen• Used for monitoring
Transtracheal wash• Isolate R. equi
Radiographs Ultrasound
Useful in evaluating the severity of pneumonia and in assessing response to therapy
Should not be used as sole criterion for prognostication and euthanasia
Prominent alveolar pattern characterized by ill-defined regional consolidation
Consolidated lesions are often more discrete nodular and cavitary• Consistent with pulmonary
abscessationLamb, 1990
In foals < 4 months: nodular lung lesions and tracheobronchial lymphadenopathy is highly suggestive of R. equi infections
In foals 4 months or older, Streptococcus zooepidemicus is another common cause of lung abscesses
http://www.ca.uky.edu/gluck/ResearchDVS.asp
Early lesions may be nonspecific irregularities of the pleural surface
In more chronic cases may see well-circumscribed, encapsulated abscesses
Very useful for evaluating severity of pneumonia and assessing response to therapy – especially if no access to thoracic radiography
Ramirez, 2004
Pulmonary consolidation
Pulmonary bronchi give lung a liver-like appearance
Hyperechoic margin indicative of air in adjacent lung
Slovis, 2005• Thoracic ultrasonography performed on foals on R. equi
endemic farms beginning at 30 days of age and repeated at 2 week intervals until weaned (16-20 weeks)
• Grading scale 0 (no evidence of pulmonary consolidation) to 10 (entire lung affected)
All foals with a graded pulmonary lesion were placed on antibiotics:• Azithromycin (10 mg/kg, q 24 h, PO for 7 days and then every
other day)• Rifampin (5 mg/kg, q 12 h, PO)• Treatments continued until ultrsonographic resolution was
determined
Farms that implemented thoracic ultrasonographic monitoring had no mortalities, and a marked reduction of clinical disease
Giguère S. Rhodococcus equi infections. In Smith BP, ed. Large Animal Internal Medicine, 4th ed (St. Louis, MO: Mosby Elsevier, 2009) pp. 510-20.
Lamb CR, O’Callaghan MW, Paradis MR. Thoracic radiography in the neonatal foal: A preliminary report. Vet Radiol Ultrasound 1990; 31: 11-6.
Ramirez S, Lester GD, Roberts GR. Diagnostic contribution of thoracic ultrasonography in 17 foals with Rhodococcus equi pneumonia. Vet Radiol Ultrasound 2004; 45: 172-6.
Slovis NM, McCracken JL, Mundy G. How to use thoracic ultrasound to screen foals for Rhodococcus equi at affected farms. AAEP Proceedings 2005; 51: 274-8.