Rhodococcus Equi Infection Research Articles

Intracranial abscess caused by Rhodococcus equi infection in a foal

A 4-month-old Missouri Fox Trotter colt was examined for a 5-week history of head tilt after treatment for suspected pulmonary Rhodococcus equi infection. Computed tomography revealed osteolysis of the occipital, temporal, and caudal portion of the parietal bones of the left side of the cranium. A soft tissue mass compressing the occipital region of the cerebral cortex and cerebellum was associated with the osteolytic bone. A rostrotentorial-suboccipital craniectomy approach was performed to remove fragmented occipital bone, debulk the intracranial mass, and obtain tissue samples for histologic examination and bacterial culture. All neurologic deficits improved substantially within 3 days after surgery. Bacterial culture of the resected soft tissue and bone fragments yielded R equi. Intracranial surgery in veterinary medicine has been limited to dogs and cats; however, in select cases, extrapolation of surgical techniques used in humans and small animals can assist with intracranial procedures in horses.

Recurrent Rhodococcus equi infection with fatal outcome in an immunocompetent patient

The majority of human Rhodococcus equi infections occur in immunocompromised hosts, especially those with AIDS, and infection in immunocompetent patients is rare. Reported here is a case of R. equi infection in a seemingly healthy patient with a very complicated course. Despite neurosurgery and prolonged antibiotic therapy the patient deceased.

Immune response to Rhodococcus equi infection in high and low antibody-producer mice (selection IV-A)

Rhodococcus equi is a gram-positive, facultative intracellular bacterium, which infects macrophages and causes rhodococcal pneumonia and enteritis in foals. Recently, this agent has been recognized as an opportunistic pathogen for immunocompromised humans. Several murine experimental models have been used to study R. equi infection. High (HIV-A) and Low (LIV-A) Antibody (Ab)-producer mice were obtained by bidirectional genetic selection for their ability to produce antibodies against sheep and human erythrocytes (Selection IV-A). These strains also maintain their phenotypes of high and low responders for antigens other than those of the selection (multiespecific effect). A higher macrophage activity in LIV-A mice has been described for several intracellular infectious agents, what could be responsible for their intense macrophage Antigen (Ag)-processing and low Ab production. Because of these differences, LIV-A mice were found to be better in triggering an effective immune response towards intracellular pathogens. The objective of this work was to evaluate the macrophage activity and to characterize the immune response of IV-A mice. HIV-A and LIV-A mice were intravenously infected with 2.0x10CFU of Rhodococcus equi ATCC 33701+. With regards to bacterial clearance and survival, LIV-A mice were more resistant to virulent R. equi than HIV-A mice. LIV-A mice presented a higher endogenous production of hydrogen peroxide (H2O2) and nitric oxide (NO) by splenic, pulmonary, and peritoneal cells than HIV-A mice. This work showed that increased TNF-α, H2O2, and NO levels are important components of the immune response in rhodococcosis, and that the Selection IV-A maintained the multiespecific effect and the polygenic control of humoral and cellular responses to R. equi.

Caprine vertebral osteomyelitis caused by Rhodococcus equi : clinical communication

There have been reports of Rhodococcus equi infections in goats in Australia, America and India. In this study, R. equi was isolated from an inflamed vertebra in a Boer goat in South Africa. At autopsy, there was a purulent inflammatory reaction in the 1st cervical vertebra. Histopathologically, a neutrophilic infiltration was encountered in the bone. Aerobic culture of swabs collected from the abscesses yielded R. equi in pure culture that was identified on biochemical tests. R. equi has become important as the cause of an opportunistic infection in people suffering from HIV.

Assessment in mice of vapA–DNA vaccination against Rhodococcus equi infection

There is a need to produce a vaccine against Rhodococcus equi pneumonia in foals in which immunity against infection is largely based on a type 1, cell-mediated, immune response. The VapA protein of the virulence plasmid of R. equi is highly immunogenic. To assess the potential of vapA-DNA to produce immunity, C57BL/6 and BALB/c mice were immunized with a DNA vaccine constructed from vapA incorporated into pcDNA3.1. The plasmid construct expressed VapA in a COS-7 cell line. Intramuscular immunization of mice resulted in enhanced clearance of R. equi from the liver of intravenously challenged mice compared to non-immunized controls. This effect was more marked when pORF-IL-12, a plasmid expressing murine IL12, was included with the vaccine. Antibody developed to VapA, with an IgG2a response being more marked in mice immunized with pcDNA-vapA than in non-immunized or in mice immunized with the mixed vapA and IL-12 plasmid constructs. In conclusion, this study has shown for the first time that DNA immunization with vapA enhances the immune responses of mice against R. equi infection, that the IgG subisotype response is consistent with a type 1-based immune response, and that this can be enhanced by injection of the IL-12 gene.

VapB-positive Rhodococcus equi infection in an HIV-infected patient in Japan

Rhodococcus equi, a bacterium present in soil, is a common cause of pneumonia in foals. This organism has been recognized as an opportunistic pathogen in humans, typically causing infection in immunocompromised hosts such as HIV-infected patients and organ transplant recipients. However, human infection with R. equi has not been reported in Japan except in a case involving a laboratory worker. We report the first human case of VapB-positive R. equi pneumonia, which involved an HIV-infected patient living in an urban area in Japan. The patient was treated successfully with 450 mg rifampicin and 600 mg tosufloxacin, even though his CD4+ lymphocyte count at the time of diagnosis was 10/microl. The patient's dogs were suspected in the epidemiology of this infection, but unfortunately we could not isolate the organism from canine-associated specimens in this case. R. equi infections in companion animals have been thought to be very rare, but they may be increasing in dogs. Therefore, further epidemiological research may clarify the prevalence of R. equi infection and the factors predisposing dogs to this infection.

Thoracic Ultrasonography

Thoracic ultrasonography is now an integral part of equine practice. Thoracic ultrasonography provides the veterinarian with diagnostic information about the lung, pleural cavity, and mediastinum that is readily obtainable in the field. The presence or absence of pleural fluid can be determined, along with its character; the lung affected or most severely affected can be determined and pulmonary atelectasis, consolidation, abscess, and necrosis can be differentiated. The ultrasonographic examination can be used as a screening tool for horses in an outbreak of equine influenza, looking for pulmonary consolidation, or in foals with suspected Rhodococcus equi infection, looking for pulmonary abscesses. An ultrasound-guided biopsy can be performed to further characterize the pulmonary pathology in horses when the sonographic findings are consistent with several differential diagnoses (pulmonary fibrosis, metastatic neoplasia, and granulomatous pneumonia). The information obtained on the initial thoracic ultrasound examination can be used to formulate a prognosis for horses with pleuropneumonia and pulmonary abscesses.

Nramp1 deletion does not confer susceptibility to Rhodococcus equi infection in mice.

Rhodococcus equi is an intracellular bacterium that causes pneumonia in immunocompromised people and foals. The Nramp1 gene influences susceptibility to a variety of intracellular bacteria (including mycobacterial species), but not to Mycobacterium tuberculosis. In this study, we demonstrate that mice functionally deleted of the Nramp1 gene were not more susceptible to infection with virulent R. equi (ATCC 33701) than wild-type mice. Susceptibility of mice to infection with the intracellular bacterium R. equi is more similar to that of M. tuberculosis than to other intracellular bacteria, including other mycobacteria.

Infection: Animal and Human Health

With the advent of AIDS, Rhodococcus equi infection has become more common in humans. Identification of virulence-associated antigens and virulence

First cases of animal diseases published since 2000. 4. Horses1

Summary In this fourth article of a series of papers listing first case reports of animal diseases published since 2000, the following six cases of horse diseases are discussed: - Disseminated metastatic intramedullary melanoma. - Lipoma of the extensor tendon sheaths. - Meningoencephalomyelitis in a neonatal foal due to Salmonella agona infection. - Neuronal ceroid lipofuscinosis. - Placentitis due to Rhodococcus equi infection. - Right atrial diverticulum in a foal. After a short introduction, the bibliographical data, the abstract of the author(s), and some additional information derived from the article are given. The article will be regularly updated adding overlooked as well as new first reports.

Disposition of oral clarithromycin in foals.

Clarithromycin offers numerous advantages over erythromycin and thus, is an attractive alternative for the treatment of Rhodococcus equi infections in foals. The disposition of clarithromycin was investigated in 6 foals after intragastric administration at a dose of 10 mg/kg body weight. Detectable serum concentrations of clarithromycin were found in 3 of 6 foals at 10 minutes and in all foals by 20 minutes post-administration. Time to peak serum concentration (Tmax) was 1.5 hours and peak serum concentration (Cmax) was 0.92+/-0.17 microg/ml. Mean serum concentrations decreased to 0.03 microg/ml at 24 h. No adverse reactions were noted during or after IG administration in any of the foals. Based on the pharmacokinetic parameters, the MIC90 of R. equi isolates, and predicted steady state concentrations, an oral dose of 7.5 mg/kg given every 12 hours would appear appropriate for the treatment of R. equi infections in foals.

Gas exchange during intense exercise in Standardbreds with earlier Rhodococcus equi pneumonia.

It is not known if pulmonary function and gas exchange during exercise are altered after pyogranulomatous pneumonia caused by Rhodococcus equi infection in the foal. The aim was to evaluate whether pulmonary gas exchange during high intensity exercise was altered in mature Standardbreds with a history of R. equi pneumonia as foals. In 7 foals, R. equi pneumonia was confirmed and treated. At age 3 years, when these horses were subjected to professional training, an inclined treadmill exercise test including 4 speeds was performed. Samples were collected when a steady state in VO2 was obtained. Red cell volume, heart rate, respiratory rate, and systemic and pulmonary mean arterial pressures were measured and cardiac output calculated. Oxygen and carbon dioxide tensions in arterial and mixed venous blood were analysed. The alveolar ventilation and the alveolar-arterial oxygen tension difference were determined. Pulmonary gas exchange was assessed and the ventilation-perfusion distribution, VA/Q, was estimated by the multiple inert gas elimination technique. Ventilation-perfusion mismatch and shunt were determined and diffusion limitation calculated. The gas exchange in Standardbred trotters previously infected with R. equi and successfully treated was not compromised during intense treadmill exercise compared with reference values for healthy, fit Standardbreds. We conclude that adult Standardbreds trotters with diagnosed R. equi pneumonia as foals, can achieve an adequate gas exchange at a workload close to VO2peak.

Rhodococcus equi: an emerging pathogen.

More than 100 cases of Rhodococcus equi infection have been reported since the first description of human disease caused by this organism. The vast majority of patients infected with R. equi are immunocompromised, and two-thirds have human immunodeficiency virus infection. The clinical manifestations of R. equi infection are diverse, although 80% of patients have some pulmonary involvement. The organism is easily cultured from specimens of infected tissue or body fluid, but it may be misdiagnosed as a contaminant. Treatment is often prolonged, and relapses at distant sites are common. This article summarizes the history, diagnosis, clinical features, and treatment of infection with this emerging pathogen.

A serological survey of Rhodococcus equi infection in foals in central Italy: comparison of two antigens using an ELISA test

A serological survey of Rhodococcus equi infection was carried out on 602 blood samples collected from foals in central Italy. The assay was performed with an ELISA test using two different antigens prepared with reference strains of R. equi, ATCC 33071 and ATCC 6939. A positive reaction was obtained on 81 serum samples (13.45%) (OD≥0.3) using antigen ATCC 33071, and on 73 serum samples (12.12%) using antigen ATCC 6939. Although the frequency of the disease was not high, the serological positivity was about 13%. There was no statistically significant difference between males and females. The ELISA test using either Antigen 33071 or Antigen 6939 is a rapid and reliable tool for detecting antibodies against R. equi in foals.

Rhodococcus equi infection in transplant recipients: a case of mistaken identity and review of the literature

The incidence of Rhodococcus equi infection in solid-organ transplant recipients continues to rise throughout the world. Unfortunately, this opportunistic pathogen is still underestimated and potentially disregarded by physicians and microbiology laboratories due to its morphology on Gram staining. Pulmonary involvement is the most common finding in the immunocompromised host. We report a case of a 63-year-old heart-transplant recipient who presented with increasing fatigue and nonproductive cough for 3 weeks. After full evaluation, a lung abscess was demonstrated by thoracic computerized tomography (CT). Blood and sputum cultures were remarkable for heavy "diphtheroids." Although the Gram-stain result was initially interpreted as a contaminant, a clinical suspicion for Rhodococcus assisted in further investigation. Broncheoalveolar lavage and CT-guided biopsy of the lung abscess revealed heavy growth of diphtheroids. However, further evaluation by a reference laboratory demonstrated mycolic acid staining consistent with R. equi. Surgical drainage and prolonged antibiotic therapy resulted in complete remission of the pneumonia and abscess. This represents the fourth reported case of R. equi infection in a heart transplant recipient. It is imperative that all physicians and laboratory staff consider R. equi when an immunocompromised patient has any type of pneumonia, especially with abscess formation.

Placentitis, fetal pneumonia, and abortion due to Rhodococcus equi infection in a Thoroughbred.

Rhodococcus equi is a rare cause of equine abortion. This report describes pyogranulomatous placentitis and fetal pneumonia in a case of abortion from a Thoroughbred mare. Numerous Gram-positive coccobacilli were noted histologically within macrophages in placental and pulmonary lesions. Rhodococcus equi was isolated in pure culture from the placenta, lung, liver, kidney, and stomach content. This is the first description of placentitis due to Rhodococcus equi infection in a horse.

Detection of antibodies against Rhodococcus equi in Alpaca (Lama pacos) in Italy.

After isolating the two virulent strains of Rhodococcus equi from Alpaca, a serological survey of Rhodococcus equi infection was carried out on 57 blood samples of Alpaca collected in Central Italy. The survey was performed with an ELISA test using a reference R. equi strain as antigen (ATCC 33701). Four (7.0%) sera (OD greater or equal to 0.3) tested positive, while five (8.77%) were considered doubtful (OD between 0.2 and 0.3). This is the first serological survey of R. equi infection in Alpaca in Italy. The results indicate that besides the horse R. equi infection could also affect some ruminant species. The ELISA test was recently introduced as a reliable diagnostic method in horses and was adapted to alpaca.

Rhodococcus equi Infection in Goat: Apropos of Two Cases

Rodriguez, J.L., Acosta, B., Navarro, R. and Gutierrez, C. 2000. Rhodococcus equi infection in goat: Apropos of two cases. J. Appl. Anim. Res., 18:149–151. Two cases of Rhodococcus equi infection in Spanish goats have been described. Clinical signs were chronic weight loss, agalactia, fever, prone position and apparent abdominal pain in one of them. Multifocal well encapsulated scattered abscess were observed in liver. Stress, sanitary deficiencies and moderate cold environment few months ago could have caused the establishment of infection.

Rhodococcus equi and HIV-1 Infection in Uganda

Objectives: To describe three cases of Rhodococcus equi infection in a cohort of HIV-1 infected adults in Entebbe, Uganda and to compare this to the rates and presentation of tuberculosis in this cohort.Methods: Consecutive HIV-1 infected adults registering with a community HIV/AIDS clinic in Entebbe were enrolled in a cohort between October 1995 and June 1998 as part of an intervention trial of pneumococcal polysaccharide vaccine. Participants were routinely reviewed every 6 months and had open access to the clinic when unwell. Standard protocols were followed for investigation and management of illness. Microbiological investigations followed standard procedures.Results: 1372 (71% female) study participants were followed for 2141 person years of observation (pyo). Rhodococcus equi was isolated from three study participants from blood, a lymph node aspirate and stool. The individuals were undergoing investigation of acute pneumonia, acute cough with cervical lymphadenopathy and chronic fever with wasting, respectively. The clinical features of these cases are described. All had a CD4 T-cell count of <300/ml. The rate of R. equi infection in the cohort was 1.4/1000 pyo. There were 132 cases of pulmonary and extrapulmonary tuberculosis in the cohort which were diagnosed either microbiologically or clinically. The rate of laboratory confirmed mycobacterial disease was 50.1/1000 pyo. The ratio of mycobacterial disease to R. equi disease was 36:1 (95% CI 11–113:1).Conclusions: Rhodococcus equi infection occurs in HIV-1 infected adults in Africa. The infection is clinically indistinguishable from pulmonary and extra-pulmonary tuberculosis in the cohort described here. Although the rate of R. equi disease is much less than that of tuberculosis, it is important to consider it in the differential diagnosis of tuberculous infection in cases which are smear negative. Rhodococcus equi infection is probably underdiagnosed in Africa due to a lack of microbiological facilities and its resemblance to common commensal organisms.

Immunohistochemical Detection of Virulence-associated Rhodococcus equi Antigens in Pulmonary and Intestinal Lesions in Horses

Two horses with Rhodococcus equi infection were examined post mortem by an immunohistochemical method (peroxidase–antiperoxidase; PAP) with a monoclonal antibody (Mab 10G5) to the 15–17 kDa antigen of R. equi. One of the horses was also examined bacteriologically, R. equi being isolated in culture. Immunolabelling with this Mab was marked and widespread. On the other hand, the immunohistochemical reactivity of infected macrophages with a polyclonal antibody specific for lysozyme was slight. Thus, Mab 10G5 would appear to be a useful diagnostic reagent in R. equi infection, with or without cultural confirmation.