Rhodococcus Flashcards
What is the definitive diagnosis method for pneumonia caused by R. equi?
Bacteriologic culture or amplification of the vapA gene using PCR from a tracheobronchial aspirate (TBA).
What clinical signs and evidence are crucial for diagnosing R. equi pneumonia in a foal?
Clinical signs of lower respiratory tract disease, cytological evidence of septic airway inflammation, and radiographic/ultrasonographic evidence of bronchopneumonia.
Why is PCR amplification of vapA not a standalone method for diagnosis?
It does not permit identification of other bacterial pathogens and in vitro antimicrobial susceptibility testing of R. equi isolates.
What is the recommended treatment for R. equi pneumonia?
The combination of a macrolide (erythromycin, azithromycin, or clarithromycin) with rifampin
What evidence exists regarding the prognosis of foals infected with macrolide- and rifampin-resistant isolates of R. equi?
Foals infected with resistant isolates might have a worse prognosis than foals infected with susceptible isolates.
How is the definitive diagnosis for extrapulmonary disorders caused by R. equi established
Bacteriologic culture or PCR amplification of vapA from samples from the site of infection.
Why is the diagnosis of enterocolitis caused by R. equi problematic?
Isolation of R. equi from feces cannot be taken as evidence of enterocolitis caused by R. equi.
What is the recommended treatment for extrapulmonary disorders caused by R. equi?
The combination of a macrolide with rifampin.
Why is implementing screening recommended for controlling R. equi pneumonia at farms with a recurrent history of affected foals?
Early identification through screening can aid in controlling the disease.
What is the recommendation regarding environmental interventions to control or prevent R. equi pneumonia?
There is inadequate evidence to recommend environmental interventions.
Why is chemoprophylaxis with macrolides or other antimicrobial drugs not recommended for R. equi pneumonia?
Conflicting evidence of efficacy and concerns for promoting resistance.
What is the recommended approach for preventing R. equi pneumonia through passive immunization?
Administration of commercially available and licensed plasma containing antibodies against R. equi.
Is active immunization of mares or foals currently recommended for controlling or preventing R. equi pneumonia?
No, there is inadequate evidence to recommend active immunization.
Which diagnostic tests aid in suspecting R. equi pneumonia?
WBC count, fibrinogen concentrations, ultrasonography, and radiography.
What diagnostic criteria were more likely to be found in foals with R. equi pneumonia than in foals with pneumonia caused by other bacteria in one study?
WBC >20,000 cells/µL, fibrinogen concentration >700 mg/dL, and evidence of pulmonary abscessation.
Why are serological tests for R. equi problematic as diagnostic tools?
hey have either low sensitivity and specificity or both, and changing cut-off values sacrifices one for the other.
What does the presence of antibodies against R. equi indicate?
It indicates exposure, subclinical infection, or maternal transfer but doesn’t confirm clinical disease.
Why should PCR amplification of vapA complement bacterial culture rather than replace it?
It may be more sensitive but increases false positives, and it will not identify other bacterial pathogens present.
What is the significance of isolating R. equi from nasal or fecal swabs?
Culturing R. equi from these swabs does not confirm disease, as healthy horses can harbor the bacterium
Why can in vitro effectiveness of antimicrobial agents against R. equi differ from their in vivo effectiveness?
In vivo effectiveness varies due to factors like poor cellular uptake.
What is the historical treatment choice for R. equi pneumonia, and why was it considered ineffective in some cases?
Historical treatments like penicillin and gentamicin were ineffective in vivo despite in vitro sensitivity due to poor tissue penetration.
What is the current preferred treatment for R. equi pneumonia, and why is it recommended?
The combination of rifampin and macrolides (erythromycin, clarithromycin, or azithromycin) is recommended, showing reduced foal mortality.
Why is the combination of macrolides and rifampin considered synergistic for treating R. equi pneumonia?
It is synergistic both in vitro and in vivo, reducing the likelihood of R. equi developing resistance to either drug.
Why is azithromycin not considered acceptable for chemoprophylaxis?
Azithromycin’s potential for resistance emergence poses concerns, and macrolide resistance is associated with a worse prognosis.
What challenges are associated with alternative antimicrobial agents for treating R. equi infections?
Limited data and lack of established preferences for antimicrobial agents in treating foals with isolates resistant to macrolides and rifampin.
What is the role of oxygen therapy in treating R. equi pneumonia, and how is it administered?
Humidified oxygen, administered through pharyngeal insufflation for moderately hypoxemic foals and percutaneous transtracheal oxygenation for severely hypoxemic patients.
What is the role of nebulization in R. equi pneumonia treatment, and what are its limitations?
Nebulization with saline, antimicrobial agents, or bronchodilators is advocated, but limited data exist to support or refute these therapeutic practices
What considerations are involved in managing septic arthritis or osteomyelitis in foals with R. equi infections?
Foals with septic arthritis or osteomyelitis may require local treatments, including joint lavage, surgical debridement, and regional limb perfusion with antimicrobial agents.
What is the prognosis post-erythromycin and rifampin treatment?
88% survival reported, and referral center studies show survival ranging between 59-72%.
What impact do screening programs have on the prognosis of R. equi pneumonia on farms?
Farms with screening programs report nearly 100% survival.
Are there significant differences in performance metrics for horses recovering from R. equi pneumonia?
No significant differences observed in performance metrics, and overall prognosis for uncomplicated treatment is excellent.
Why is diligent screening crucial for controlling R. equi pneumonia?
Clinical signs may not appear until pathological changes are well progressed, and early detection improves therapeutic outcomes.
What is the cumulative incidence of clinical signs of pneumonia attributed to R. equi?
10–20% from birth to weaning.
What is the role of ultrasonography in R. equi pneumonia screening, and what are its advantages and disadvantages?
Ultrasonography is quick, potentially more sensitive than radiography, specific for pulmonary pathology, and shows potential mortality reduction. However, it has disadvantages like increased costs and labor.
What environmental factors influence the occurrence of R. equi pneumonia?
Factors include the density of mares and foals, soil and geochemistry, manure management, airborne concentrations, foaling at pasture, and isolation of pneumonic foals.
What challenges are associated with chemoprophylaxis using azithromycin for R. equi pneumonia prevention?
Conflicting study results, potential for resistance emergence, and lack of a controlled study documenting reduction in mortality.
What challenges are associated with gallium maltolate as a chemoprophylactic option for R. equi pneumonia?
Despite promising preclinical findings, it did not show efficacy in preventing R. equi pneumonia in a placebo-controlled trial.
What challenges are associated with passive immunization using hyperimmune plasma (HIP) for R. equi pneumonia?
Risks include trauma during handling, adverse reactions to transfusions, time and labor intensity, and cost. HIP transfusion is not completely effective, requiring continued screening and monitoring of foals.
Why is early administration of HIP crucial, and when is the optimal timing for transfusion?
Early administration is crucial, and the optimal timing is around the 2nd day of life, with second doses at 2–4 weeks of age.
What type of responses does an effective vaccine for R. equi prevention need to induce?
Type 1 cell-mediated responses, including CD4+ Th1 lymphocytes secreting interferon-gamma and CD8+ T lymphocytes that recognize and eliminate R. equi-infected cells.
What was demonstrated in a study where neonatal foals were intragastrically inoculated with virulent R. equi?
Protection from subsequent respiratory challenges, indicating that young foals can mount protective immune responses.
