EQUINE
Welcome to the Equine NAVLE Notes: Cardiorespiratory section.
Here, veterinarians preparing for the NAVLE test will find comprehensive notes on respiratory and cardiovascular issues in horses. Explore key topics such as equine asthma, exercise-induced pulmonary hemorrhage (EIPH), atrial fibrillation, and valvular heart disease. These notes are designed to help you prepare thoroughly and confidently for the exam, ensuring you're ready to pass with flying colors.
CONTENT:
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Rhodococcus equi in Foals
Overview:
Rhodococcus equi is a Gram-positive, facultative intracellular pathogen primarily affecting foals between 1 to 6 months of age. It is a significant cause of bronchopneumonia, leading to high morbidity and mortality rates in affected animals. The pathogen is commonly found in the soil of horse farms and can cause both pulmonary and extrapulmonary infections.
Clinical Signs:
Early signs of R. equi infection are often subtle and include a slight increase in respiratory rate and mild fever. As the disease progresses, more pronounced symptoms such as cough, nasal discharge, lethargy, fever, tachypnea, and respiratory distress become evident. In advanced cases, abscess formation within the lungs is common.
Diagnosis:
Diagnosis is typically based on a combination of clinical signs, thoracic imaging, and microbiological culture. Thoracic ultrasound and radiography are key tools, with ultrasound being particularly effective in identifying peripheral lung lesions. Transtracheal wash samples can be used for cytology and culture, revealing intracellular coccobacilli. Serologic tests are not recommended for diagnosis due to their poor correlation with disease severity.
Treatment:
The standard treatment involves a combination of a macrolide antibiotic (e.g., clarithromycin or azithromycin) and rifampin. This combination is preferred due to the synergistic action of these drugs and their ability to penetrate abscesses. Treatment duration ranges from 2 to 12 weeks, depending on the severity of the infection. Monitoring is essential to adjust therapy based on the foal’s clinical response and radiographic findings.
Prevention:
Preventive measures include environmental management to reduce dust and exposure to contaminated soil, as well as early detection and treatment of subclinical infections. Vaccination strategies are still under research, with some promising developments.
Prognosis:
The prognosis for foals with R. equi pneumonia ranges from guarded to good, with survival rates between 60% and 90% if treated early and appropriately.
References:
• Merck Veterinary Manual. Rhodococcus equi Pneumonia in Foals.
• dvm360. Rhodococcus equi infection in foals: diagnosis and treatment (Proceedings)
• American Association of Equine Practitioners (AAEP). Rhodococcus Equi.
NAVLE test sample questions
Equine: Cardiorespiratory
Question 1:
Which of the following is the most reliable diagnostic method for confirming Rhodococcus equi infection in foals?
A) Serologic testing
B) Fecal flotation
C) Thoracic radiography
D) Nasopharyngeal swab culture
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Question 2:
When treating a foal diagnosed with severe Rhodococcus equi pneumonia, which combination of drugs is considered the standard therapy?
A) Doxycycline and gentamicin
B) Amoxicillin and clavulanic acid
C) Azithromycin and rifampin
D) Tetracycline and metronidazole
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Answers & Explanations
Question 1:​
Answer: C) Thoracic radiography
Explanation: Thoracic radiography is a key diagnostic tool for Rhodococcus equi in foals, particularly for identifying perihilar alveolar patterns indicative of pulmonary consolidation and abscess formation. Serologic testing is not recommended due to its poor correlation with disease severity, and fecal flotation and nasopharyngeal swabs are not effective diagnostic methods for this disease​
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Question 2:
Answer: C) Azithromycin and rifampin
Explanation: The standard treatment for severe Rhodococcus equi pneumonia in foals is a combination of a macrolide antibiotic (such as azithromycin) and rifampin. This combination is highly effective due to its synergistic activity and ability to penetrate abscesses, which are common in this disease. Alternatives like doxycycline and gentamicin are considered in cases of resistance, but they are not the first-line treatment​
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