Osteomyelitis of the scapulohumeral joint associated with Rhodococcus equi and unresponsive to antibiotherapy in a foal

This case report describes the treatment and outcome of a 3.5-month-old lame foal, with a history of pneumonia associated with Rhodococcus equi. Clinical examination identified osteomyelitis of the scapulohumeral joint. The unusual location of the Rhodococcus equi osteomyelitis unresponsive to prevention and adequate treatment led to euthanasia of the patient. Post-mortem findings confirmed bronchopneumonia due to Rhodococcus equi as well as the osteomyelitis of the scapulohumeral joint. This case highlights that Rhodococcus equi should be considered as a pathogen in extrapulmonary locations such as septic arthritis and osteomyelitis in foals with history of bronchopneumonia. Early and aggressive treatment should be considered.     

Rhodococcus equi (Prescottella equi) vaccines; the future of vaccine development

For decades researchers have been targeting prevention of Rhodococcus equi (Rhodococcus hoagui/Prescottella equi) by vaccination and the horse breeding industry has supported the ongoing efforts by researchers to develop a safe and cost effective vaccine to prevent disease in foals. Traditional vaccines including live, killed and attenuated (physical and chemical) vaccines have proved to be ineffective and more modern molecular‐based vaccines including the DNA plasmid, genetically attenuated and subunit vaccines have provided inadequate protection of foals. Newer, bacterial vector vaccines have recently shown promise for R. equi in the mouse model. This article describes the findings of key research in R. equi vaccine development and looks at alternative methods that may potentially be utilised.     

ASSOCIATION BETWEEN RADIOGRAPHIC PATTERN AND OUTCOME IN FOALS WITH PNEUMONIA CAUSED BY Rhodococcus equi

Our objective was to characterize the association between types of radiographic findings and outcome in foals with pneumonia caused by Rhodococcus equi. Admission lateral thoracic radiographs of 62 foals with culture‐confirmed R. equi pneumonia were reviewed retrospectively. A scoring system was developed to individually assess the severity of alveolar pattern, interstitial pattern, tracheobronchial lymphadenopathy, pleural effusion, and the number of nodular opacities and cavitary lesions. Individual scores were added to obtain a total radiographic score ranging from 0 (normal) to 22. Forty‐three of 62 foals (69%) survived to discharge. The median total radiographic score of nonsurvivors (14; range, 9–16) was significantly (P = 0.007) higher than that of survivors (11; range, 4–15). Foals with a total radiographic score of greater than or equal to 15 were 6.15 times (95% CI: 1.35 to 28.2) less likely to survive than foals with a lower score (P = 0.019). A multivariate logistic regression model was used to identify the potential associations between specific types of radiographic lesions and outcome. The model was statistically significant (P = 0.002) and correctly classified 75.8% of foals. Only severity of alveolar pattern and number of cavitary lesions made statistically significant contributions to the model. There was no significant association between concurrent isolation of other bacteria along with R. equi and the types or severity of radiographic lesions. Based on the results of this study, severity of alveolar pattern and number of cavitary lesions are the radiographic findings significantly associated with a poor outcome in foals with R. equi pneumonia.     

Rhodococcus equi pneumonia in an adult horse

A 20‐year‐old, Thoroughbred mare in the fifth month of gestation was examined for weight loss, pyrexia and lethargy. Physical examination, ultrasonography and radiography revealed a severe abscessing pneumonia and a dead fetus. The mare did not respond to symptomatic treatment and died suddenly. Necropsy revealed multifocal pulmonary abscessation. Rhodococcus equi was isolated from the lungs, liver and kidneys. Specific immune function of the mare and presence of the virulence associated protein A (VapA) of the R. equi isolated was not determined. It is likely that immunosuppression is required for systemic R. equi infections in adult horses; however, it is unknown if VapA is necessary to produce disease in adult horses.     

Diagnostic contribution of thoracic ultrasonography in 17 foals with Rhodococcus equi pneumonia

The aim of this retrospective study was to determine the clinical usefulness of thoracic ultrasonography compared to thoracic radiography in evaluation of Rhodococcus equi pneumonia. Criteria for patient inclusion in this study were: (1) isolation of R. equi from transtracheal aspirate, (2) radiographic evaluation of the pulmonary parenchyma, and (3) sonographic evaluation of the pulmonary parenchyma. Seventeen foals met this criteria and their medical records were reviewed. Pyogranulomatous pneumonia was identified radiographically in 13 foals. Severe consolidative pneumonia with no detectable abscessation was identified radiographically in three others. Both consolidation and abscessation were identified radiographically in one. In this foal only consolidation was ultrasonographically identified. Ultrasonographically, pulmonary abscessation was identified in 12 foals and pulmonary consolidation with no detectable abscessation was identified in three others. Sonographic examination allowed detection of only pleural irregularities in one foal, which was subsequently found to have pyogranulomatous pneumonia radiographically. Results indicate that ultrasonography may be an accurate alternative imaging modality for detection of pulmonary pathology attributed to R. equi pneumonia in foals when thoracic radiography is not available.     

Septic pyomyositis,multiple pelvic osteomyelitis and thrombosis in a Thoroughbred foal

Multiple septic osteomyelitis, septic thrombi and septic arthritis are recognised as possible complications of sepsis; however, there are few reports of localised pyomyositis in association with septic arterial thrombosis in foals. A 1-month Thoroughbred colt was presented for investigation of acute and progressive left hindlimb lameness. Physical and laboratory examinations were performed. Ultrasonographic, radiographic and computed tomographic examinations revealed the presence of multiple abscesses and areas of osteomyelitis localised to the gluteal muscles, coxal bone and lumbar spine respectively. Considering the poor prognosis, the foal was subjected to euthanasia. Necropsy confirmed the diagnostic imaging findings and revealed the presence of an extensive septic thrombus, affecting the internal iliac artery, and a single pulmonary abscess. Streptococcus equi subsp. zooepidemicus was isolated from all lesions.     

Tibial osteomyelitis caused by Rhodococcus equi in a mature horse

A 7‐year‐old Paint mare presented for evaluation of a swollen right hindlimb of approximately 6 weeks' duration. Ultrasonography and radiography suggested a severe osteomyelitis and abscessation of the right tibia. Previous treatment included systemic antimicrobial therapy using procaine penicillin G (22,000 u/kg bwt, q. 12 h, i.m.) and gentamicin sulfate (6.6 mg/kg bwt, q. 24 h, i.v.) initially followed by oral doxycycline (10 mg/kg bwt, q. 12 h, per os) and rifampin (5 mg/kg bwt, q. 12 h, per os). Based on the poor prognosis the mare was subjected to euthanasia. Necropsy results subsequently revealed a severe, chronic, focal, necrotising osteomyelitis with localised cellulitis and abscessation. Rhodococcus equi was isolated from the tibia, subcutaneous abscess and from a pectoral abscess found at necropsy. Immunological testing of blood samples obtained ante mortem revealed normal blood lymphocyte phenotyping, but markedly increased IgG and IgM concentrations, indicating an active humoural response. While there have been reports of Rhodococcus equi infection in mature horses this is an area previously unreported in the literature.     

Air sampling in the breathing zone of neonatal foals for prediction of subclinical Rhodococcus equi infection

Reasons for performing the study: Disease caused by Rhodococcus equi is a significant burden to the horse breeding industry worldwide. Early detection of rhodococcal pneumonia, albeit important to minimise treatment costs, is difficult because of the insidious nature of the disease and the lack of definitive diagnostic tests. Objectives: To investigate air sampling from the breathing zone of neonatal foals as a predictor of subsequent rhodococcal pneumonia. Methods: Air samples were collected from the breathing zone of 53 neonatal foals (age ≤10 days) and again at the time of routine ultrasonographic screening for R. equi pneumonia (age 1–2 months). Results: Pneumonia was diagnosed ultrasonographically in 23% of foals. Virulent R. equi was detected in air from the breathing zone of 19% of neonatal foals and 45% of foals at age 1–2 months. There was no association between virulent R. equi in the breathing zone of foals and the subsequent ultrasonographic diagnosis of rhodococcal pneumonia. The median concentration of virulent R. equi in the breathing zone of both neonates (0 [range 0–4] colony‐forming units [cfu]/250 l) and older foals (0 [range 0–3] cfu/250 l) was not significantly different from that in background air samples (0 [range 0–6] cfu/250 l). There was no difference in the concentration of virulent R. equi in the breathing zone of older foals that were diagnosed with rhodococcal pneumonia or clinically normal foals. Conclusion: Detection of virulent R. equi in air from the breathing zone was not a positive predictor of rhodococcal pneumonia in foals up to age ≤2 months. Potential relevance: Selective culture of air samples from the breathing zone of young foals is not better at diagnosing rhodococcal pneumonia than early ultrasonographic screening. However, culture of air samples from the breathing zone of older foals remains a useful herd‐based epidemiological tool.     

Haematogenous septic arthritis,physitis and osteomyelitis in foals: A tutorial review on pathogenesis,diagnosis, treatment and prognosis. Part 1

Haematogenous septic arthritis, physitis and osteomyelitis (SAPO) is a potentially debilitating or even life-threatening disease entity encountered in foals of all ages between birth and approximately 7 months old. Correct, and complete, diagnosis and successful treatment require collaboration between specialties including medicine, anaesthesia, diagnostic imaging, surgery and rehabilitation services. However, in order to succeed, it is important that all specialties have an overall knowledge of all aspects of the disease complex. Therefore, the aim of this review is to give an overview of aetiology, presenting complaints, clinical findings, diagnostic imaging, treatment, rehabilitation and prognosis. Part one deals with all aspects of aetiology and how to make a diagnosis. Part two deals with all aspects of treatment, rehabilitation and prognosis.     

Multiple extra-pulmonary disorders associated with Rhodococcus equi infection in a 2-month-old foal

A 2-month-old Thoroughbred filly was referred to Hagyard Equine Medical Institute for further evaluation of acute pyrexia and a suspected intra-abdominal abscess based on abdominal ultrasonography performed in the field. Initial examination revealed bilateral uveitis, polysynovitis, a large internal abdominal abscess and pneumonia. A transtracheal wash confirmed the presence of a multi-sensitive strain of Rhodococcus equi. Anaemia and thrombocytopenia were noted during hospitalisation. Results of a Coombs test were consistent with an immune-mediated haemolytic process. Recurrent pyrexia, abdominal discomfort and severe respiratory distress unresponsive to intensive medical support motivated euthanasia followed by necropsy after 30 days of treatment. Overall, six extra-pulmonary disorders were simultaneously diagnosed despite the lack of pulmonary pyogranulomas.     

Medical management of a large intra-abdominal mass caused by Rhodococcus equi in a foal

A 4-month-old Thoroughbred filly presented with pyrexia, inappetence and diarrhoea. Abdominal ultrasonography revealed a multilobulated abdominal mass that was determined to be associated with the caecum using computed tomography. Computed tomography also identified mesenteric lymphadenopathy and a pulmonary mass in the left caudal lung lobe. Percutaneous aspiration of the abdominal mass yielded pure growth of Rhodococcus equi. The filly responded in a positive fashion to the administration of clarithromycin, rifampin and gallium maltolate. Follow-up computed tomography revealed complete resolution of the abdominal mass and lymphadenopathy. Extrapulmonary disorders associated with R. equi should be considered even when thoracic ultrasonography reveals no evidence of pulmonary pathology. Although intra-abdominal abscesses have a grave prognosis, successful treatment is possible. Gallium maltolate can be safely administered to foals and may improve patient outcomes.     

Septic arthritis of the first and second cervical vertebral articulations with vertebral osteomyelitis in a foal caused by Salmonella

A case of infectious arthritis of a cervical vertebral articulation and vertebral osteomyelitis in a foal caused by Salmonella is described. Ultrasound images of the cervical facet joints were suggestive of septic arthritis and ultrasound facilitated needle placement for arthrocentesis and joint lavage. Due to the uncommon location of the infection, diagnosis of septic arthritis was not immediate and, despite aggressive intra‐articular lavage and instillation of appropriate intra‐articular antibiotics after hospitalisation, we were unable to resolve the infection in this foal. Radiographs did not show evidence of osseous involvement until later in the course of the infection. Septic arthritis should be suspected in cases with similar clinical and laboratory findings and radiographic changes may not be present early in the course of infection. Ultrasound imaging provided the most useful diagnostic information regarding infection of the cervical joints, facilitating both diagnosis and treatment.     

Arthrotomy,curettage and medical management of septic arthritis and osteomyelitis of the temporomandibular joint in a horse

Osteomyelitis and/or bone sequestra are commonly reported in equids following traumatic wounds. This report describes the clinical management and outcome following an arthrotomy of the temporomandibular joint of a 1-year-old Quarter Horse gelding with septic osteomyelitis and arthritis. Computed tomography was used for further assessment of the lesions within the temporomandibular joint and helped guide surgical planning.     

Successful management of multiple extrapulmonary complications associated with Rhodococcus equi pneumonia in a foal

This report describes the diagnosis and successful treatment of multiple extrapulmonary sequelae of Rhodococcus equi (R. equi) pneumonia in a 3‐month‐old filly. Bilateral uveitis and hyphaema, haemolytic anaemia and polysynovitis developed in this foal and were likely due to immune‐mediated mechanisms. The challenges associated with diagnosis and treatments of these extrapulmonary disorders are discussed. The filly was treated initially with clarithromycin and rifampin; however, a blood transfusion and immunosuppressive therapy with dexamethasone were required due to progressive haemolysis and for treatment of uveitis and polysynovitis. Bilateral hyphaema was successfully treated with intracameral injections of a recombinant tissue plasminogen activator. The development of antimicrobial resistance in R. equi was an additional challenge encountered in the management of this case and emphasises the importance of culture and in vitro antimicrobial susceptibility testing of isolates from foals with R. equi pneumonia. Extrapulmonary disorders associated with R. equi pneumonia are likely underdiagnosed and associated with a poor prognosis. This case highlights the importance of thorough and ongoing diagnostic assessment of foals with R. equi pneumonia and demonstrates that a successful outcome can be achieved with appropriate and directed treatment.     

Septic arthritis,navicular bursitis and osseous cyst‐like lesion in a foal

The purpose of this report is to describe the clinical, imaging and pathological findings in a Quarter Horse colt admitted to the Texas A&M University Veterinary Medical Teaching Hospital for lameness of the left forelimb and left hindlimb. A presumptive diagnosis of left forelimb septic navicular bursitis was made ultrasonographically. A cyst‐like lesion of the calcaneus was diagnosed radiographically and better characterised with computed tomography. The cyst‐like lesion of the calcaneus was caused by infection with Actinobacillus sp. and extended into the adjacent tarsocrural, proximal intertarsal and talocalcaneal joints causing septic arthritis. The owner elected for euthanasia due to the poor prognosis. The diagnoses were confirmed on histopathology.