Rhodococcus equi infection
Introduction
- Severe pyogranulomatous bronchopneumonia, mainly in foals of 1-4 months old, rare in horses older than 6 months of age.
- Cause:Rhodococcus equi Rhodococcus equi (nowPrescottella equi). Predisposing factors: stress, poor hygiene, environmental contamination, concurrent parasitism.
- Signs: generally non-specific (fever, inappetence); some cases may show coughing or nasal discharge.
- Diagnosis: bacteriology and PCR on transtracheal aspirate samples; radiology; ultrasonography; hematology.
- Treatment: combinations of antibiotics based on susceptibility testing; macrolide and rifampicin.
- Prognosis: fair to good with appropriate treatment; morbidity up to 80% in outbreaks.
Presenting signs
Common
- Inappetence, fever and depression in foals 1-4 months old.
- Fever.
- Lethargy.
- Increased respiratory rate and effort (increased abdominal effort, nostrils flaring, tachypnea).
- Cough.
- Nasal discharge (inconsistent).
Signs of extra pulmonary rhodococcal infection
- Gastroenteritis.
- Severe lameness.
- Gastroenteritis.
- Uterine infection with abortion Abortion: overview .
- Neurological deficits.
- Immune-complex deposition → uveitis, hypopyon, anemia, thrombocytopenia.
Acute presentation
- Acute suppurative bronchopneumonia with dyspnea.
Geographic incidence
- Worldwide.
- Sporadic.
- Common in hot conditions.
- Enzootic on some farms.
- May be unrecognized.
Age predisposition
- 1-4 months.
- Adults (rare) with the exception of animals with immunodeficiencies.
Public health considerations
- Humans with immune deficiencies could develop infection.
Cost considerations
- An important cause of foal loss.
- Long-term antibiotic therapy is important to avoid relapses.
- Intensive monitoring of foals during risk periods - daily temperature monitoring, serial monitoring of thoracic ultrasonography and radiography, serial monitoring of leukocyte count and fibrinogen.
Special risks
- Foals being treated with macrolides are prone to hyperthermia.
Pathogenesis
Etiology
- Rhodococcus equi Rhodococcus equi .
- Foals infected at an early age by inhalation or ingestion ofR. equi.
- Fairly prolonged incubation period (9 days to 4 weeks experimentally).
- R. equiis carried passively in the equine intestine and shed in feces.
Predisposing factors
General- Bacterial contamination of environment, especially in dry fecal material.
- Decline in maternally derived immunity.
- Immature local respiratory tract immunity in young foals.
- Stress.
- Poor hygiene.
- Parasitism, especially migrating larvae.
- Immune compromise.
- Poor ventilation/dusty environment.
Specific
- Virulent strains ofR. equi; presence of VaPA plasmid.
- Equine herpesvirus Equine herpesvirus , may be a trigger for the development of rhodococcal pneumonia.
- Genetic predisposition has been suggested.
Pathophysiology
- Infection likely occurs shortly after birth, clinical signs rarely seen prior to one month of age.
- Inhalation ofR. equiin dust → survives in alveolar macrophages → pyogranulomatous inflammation → abscesses in lungs and hilar lymph nodes → progressive destruction of lung tissue → acute or chronic suppurative bronchopneumonia.
- Stimulates development of acute or chronic pyogranulomatous pneumonia.
- Hematogenous spread from lungs or gastrointestinal system → septic arthritis/osteomyelitis.
- Immune-complex deposition → polysynovitis and uveitis, hypopyon, anemia, thrombocytopenia.
- Abscesses may form in intestines and mesenteric lymph nodes following ingestion of the organism or hematogenous spread from pulmonary infection.
- Villous atrophy, intestinal ulceration and peritonitis contribute to diarrhea, weight loss and poor growth.
- Organism may also localize in joints, bones, spleen, uterus or skin.
- Rare manifestations:
- Ulcerative lymphangitis.
- Cellulitis.
- Subcutaneous swellings and abscessation.
- Uveitis.
- Panophthalmitis.
- Nephritis.
- Hepatic and renal abscessation.
- Vertebral or paravertebral body abscessation.
Timecourse
- Incubation period: experimental data suggest 9 days to 4 weeks.
- Foals are generally infected at a very young age.
Epidemiology
- R. equipresent in feed → passes through (and may proliferate in) intestinal tract of healthy horses and other herbivores → contamination of pasture and bedding with infected fecal material → transmitted by inhalation of dust or ingestion.
- Congenital infection may also occur, via umbilical or mucous membrane exposure.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Giles C et al (2014) Rhodococcus equi (Prescottella equi) vaccines: the future of vaccine development. Equine Vet J 47 (5), 510-518 PubMed.
- Venner M, Credner N, Lammer M & Giguere S (2013) Comparison of tulathromycin, azithromycin and azithromycin-rifampin for the treatment of mild pnuemonia associated with Rhodococcus equi. Vet Rec 173 (16), 397 PubMed.
- Boyen F, Pasmans F & Haesebrouck F (2011) Acquired antimicrobial resistance in equine Rhodococcus equi isolates. Vet Rec 168 (4), 101 PubMed.
- Giguere S et al (2011) Diagnosis, treatment, control and prevention of infections caused by Rhodococcus equi. J Vet Intern Med 25 (6), 1209-1220 PubMed.
- Giguere S et al (2011) Rhodococcus equi: Clinical manifestations, virulence and immunity. J Vet Intern Med 25 (6), 1221-1230 PubMed.
- Reuss S M, Chaffin M K & Cohen N D (2009) Extrapulmonary disorders associated with Rhodococcus equi infection in foals: 150 cases (1987). JAVMA 253 (7), 855-863 PubMed.
- Davis E (2008) Rhodococcus equi in adult horses. Equine Vet Educ 20 (2), 72-73 Wiley Online Library.
- Waldridge B M, Morresey P R, Loynachan A T et al (2008) Rhodococcus equi pneumonia in an adult horse. Equine Vet Educ 20 (2), 67-71 VetMedResource.
- Muscatello G, Leadon D, Klay M, Meijer W & Gilkerson J (2007) Rhodococcus equi infection in foals: the science of 'Rattles'. Equine Vet J 39 (5), 470-478 PubMed.
- Janicek J C et al (2006) Intracranial abscess caused by Rhodococcus equi infection in a foal. JAVMA 228 (2), 251-253 PubMed.
- Cohen N D et al (2005) Study of serum amyloid A concentrations as a means of achieving early diagnosis of Rhodococcus equi pneumonia. Equine Vet J 37 (3), 212-216 PubMed.
- Chaffin M K, Cohen N D et al (2003) Foal-related risk factors associated with development of Rhodococcus equi pneumonia on farms with endemic infection. JAVMA 233 (12), 1791-1799 PubMed.
- Chaffin M K, Cohen N D & Martens R J (2003) Evaluation of equine breeding farm management and preventative health practices as risk factors for development of Rhodococcus equi pneumonia in foals. JAVMA 222 (4), 476-485 PubMed.
- Chaffin M K, Cohen N D & Martens R J (2003) Evaluation of equine breeding farm characteristics as risk factors for development of Rhodococcus equi pneumonia in foals. JAVMA 222 (4), 467-475 PubMed.
- Ainsworth D M (1999) Rhodococcal infection in foals. Equine Vet Educ 11 (4), 191-198 VetMedResource.
- Baverud V et al (1998) Clostridium difficile associated with acute colitis in mares when their foals are treated with erythromycin and rifampicin for Rhodococcus equi infection. Equine Vet J 30, 482-488 VetMedResource.
- Giguere S & Prescott J F (1997) Clinical manifestations, diagnosis, treatment and prevention of Rhodococcus equi infections in foals. Vet Microbiol 56 (3-4), 313-334 VetMedResource.
- Paradis M R (1997) Cutaneous and musculoskeletal manifestations of Rhodococcus equi infection in foals. Equine Vet Educ 9, 266-270 VetMedResource.
- Takai S (1997) Epidemiology of Rhodococcus equi infections - a review. Vet Microbiol 56 (3-4), 167-176 VetMedResource.
- Clarke A F (1989) Management and housing practices in relation to Rhodococcus equi infection of foals. Equine Vet Educ 1 (1), 30-32 VetMedResource.
- Leadon D P (1989) An outbreak involving six cases of Rhodococcus equi on a studfarm. Equine Vet Educ 1 (1), 23-24 VetMedResource.
- Keen P M (1989) Pharmacology and treatment of Rhodococcus equi infection. Equine Vet Educ 1 (1), 28-29 Ve