Unit 1 - Rhodococcus equi

Question 1

Describe the morphology and features of R. equi.

Answer 1

Gram positive, facultative intracellular bacteria.

Question 2

What population is rhodococcus equi the most common cause of pneumonia in?

Answer 2

It’s one of the most common causes of pneumonia in foals 3 weeks to 5 months of age.

Question 3

What are the clinical manifestations of R. equi?

Answer 3

Pulmonary disease is most common
Subclinical disease: sonographic lesions, but no outward respiratory signs
Clinical disease: chronic, suppurative bronchopneumonia with abscess formation
Decreased appetite, lethargy, fever, cough, tachypnea, labored breathing, +/- nasal discharge
Death

Question 4

_______ disorders (EPDs) for RE are common. 74% of foals get at least one of these.

Answer 4

extrapulmonary

Question 5

What are the common extrapulmonary disorders of rhodococcus equi?

Answer 5

Intestinal lesions
Abdominal disease
Intra-abdominal lymph node abscesses
Uveitis and polysynovitis 
Septic arthritis and osteomyelitis

Question 6

RE pathogenicity is linked to its ability to persist in and ultimately destroy _______ _______.

Answer 6

alveolar macrophages

Question 7

What is the major route of pulmonary RE infection in foals?

Answer 7

Inhalation of virulent RE

Question 8

What is an important route of exposure to RE resulting in immunity? Why can’t it be used in a widespread manner?

Answer 8

Ingestion of bacteria - it would lead to progressive seeding of the environment with virulent organisms

Question 9

True or false: Large breeding farms that have a high stocking density and a large population of transient mare / foal pairs increases the odds of RE pneumonia.

Answer 9

TRUE

Question 10

True or false: There is no compelling evidence that RE infection is contagious among foals and that affected foals should be isolated from other foals.

Answer 10

TRUE

Question 11

Describe the steps to how RE causes macrophage necrosis.

Answer 11

1. RE inhaled
2. receptor-mediated phagocytosis by alveolar macrophages
3. RE modifies the phagocytic vacuole to prevent acidification and subsequent fusion with lysosomes
4. uncontrolled intracellular RE replication
5. macrophage necrosis.

Question 12

What is the most apparent example of the role of antibody-mediated immunity to RE in foals?

Answer 12

Mares vaccinated against RE provides foals with protection against intrabronchial challenge with RE.

Question 13

The ____ _____ nature of RE suggests that a cell-mediated immunity response is likely a major component to resisting infection.

Answer 13

facultative intracellular

Question 14

How can we definitively diagnose RE?

Answer 14

identification of the organism on a TBA by bacterial culture and/or amplification of the vapA gene by PCR in a foal with clinical signs of lower respiratory tract disease, cytologic evidence of septic airway inflammation and/or radiographic or ultrasonographic evidence of bronchopneumonia

Question 15

What is the most common trend in blood analysis seen with foals infected with RE?

Answer 15

Hyperfibrinogenemia

Question 16

What ways can we image foals to monitor RE?

Answer 16

thoracic radiographs or ultrasonography

Question 17

True or false: Currently, there is no convincing data that serologic testing of RE is beneficial to the diagnosis of RE.

Answer 17

TRUE

Question 18

What are the methods of establishing a diagnosis RE pneumonia?

Answer 18

Bacterial culture or PCR amplification of VapA from a TBA.
TBA culture is a valid method for diagnosing RE pneumonia, but its sensitivity and specificity aren’t great.
PCR should be performed in addition to culture, but not as a replacement for culture.
The current data drives home the point that the results of culture and PCR must be interpreted in the context of cytologic and clinical findings.

Question 19

How do you treat foals with severe clinical pneumonia?

Answer 19

A combination of Rifampin and a macrolide, especially Clarithromycin.

Question 20

How should you treat foals with mild to subclinical RE lesions?

Answer 20

Available data highlights that foals with mild sRE have a high rate of recovery (78%) without antimicrobial therapy and this data cannot be interpreted as proof of antimicrobial efficiency.

Question 21

True or false: polymicrobial isolation from TBA negatively affects survival.

Answer 21

FALSE

Question 22

Why do researchers believe macrolide resistance to be increasing?

Answer 22

Mass treatment of sRE on endemic farms.

Question 23

What is sRE antimicrobial duration time based on?

Answer 23

Resolution of lesions on sonographic imaging. Duration is 2-12 weeks, depending on the severity of disease

Question 24

What is the most common side effect of macrolides + Rifampin?

Answer 24

Diarrhea - it’s usually self limiting and does not require specific therapy. Occasionally, hyperthermia, tachypnea, and severe enterocolitis (erythromycin) may occur.

Question 25

What is the survival rate of RE now that we have macrolide + Rifampin treatment?

Answer 25

> 80% - prognosis for athletic performance in survivors is very good

Question 26

What are the recommendations for control and prevention of RE on endemic farms?

Answer 26

Screening tests for early detection of RE pneumonia (Ultrasound, rectal temperatures, observation for cRE, etc.)
Environmental management
Chemoprophylaxis (not great and contributes to the current macrolide resistance problem.)
Passive or active immunization

Question 27

Describe how we can provide passive immunization.

Answer 27

Administration of hyperimmunized plasma obtained from horses vaccinated against RE using a variety of antigens.

Question 28

True or false: the process of actively immunizing mares and foals is extremely important in the effort of preventing RE.

Answer 28

false - goven that CMI plays an integral role in protecting from RE, immunization of the foal should be beneficial, but we are yet to make a functional vaccine that works and doesn’t actually infect the foal