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PubMed2002

Evaluation of 5 serologic assays to detect Rhodococcus equi pneumonia in foals.

OBJECTIVE: To determine the sensitivity and specificity of 5 serologic assays used to diagnose Rhodococcus equi pneumonia in foals and to determine whether any of the assays could be used to identify affected foals prior to the onset of clinical signs or to differentiate between affected and unaffected foals when clinical signs first become apparent. DESIGN: Nested case-control study. ANIMALS: 26 foals. PROCEDURE: Serum samples were obtained from all foals at 2, 4, and 6 or 7 weeks of age. Additional samples were obtained from affected foals at the time of diagnosis of R equi pneumonia and from age-matched unaffected foals. Samples were tested with 3 ELISA, an agar gel immunodiffusion assay, and a synergistic hemolysis inhibition assay. RESULTS: Sensitivity and specificity data indicated that none of the assays could be used to reliably differentiate affected from unaffected foals at any testing period. Proportions of foals that had an increase in test values between paired samples collected at 4 and 6 or 7 weeks of age were not significantly different between affected and unaffected foals. For all assays, result values increased significantly over time; however, the rate of increase was not significantly different between affected and unaffected foals. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that serologic assays, whether performed on single or paired samples, cannot be used to reliably establish, confirm, or exclude a diagnosis of R equi pneumonia in foals.

Actinomycetales Infections↗
PubMed2006

Internally controlled real-time PCR method for quantitative species-specific detection and vapA genotyping of Rhodococcus equi.

We developed a novel quantitative real-time PCR (Q-PCR) method for the soil actinomycete Rhodococcus equi, an important horse pathogen and emerging human pathogen. Species-specific quantification was achieved by targeting the chromosomal monocopy gene choE, universally conserved in R. equi. The choE Q-PCR included an internal amplification control (IAC) for identification of false negatives. A second Q-PCR targeted the virulence plasmid gene vapA, carried by most horse isolates but infrequently found in isolates from other sources. The choE-IAC and vapA assays were 100% sensitive and specific as determined using 178 R. equi isolates, 77 nontarget bacteria, and a panel of 60 R. equi isolates with known vapA+ and vapA-negative (including vapB+) plasmid genotypes. The vapA+ frequency among isolate types was as follows: horse, 85%; human, 20%; bovine and pig, 0%; others, 27%. The choE-IAC Q-PCR could detect up to one genome equivalent using R. equi DNA or 100 bacteria/ml using DNA extracted from artificially contaminated horse bronchoalveolar lavage (BAL) fluid. Quantification was linear over a 6-log dynamic range down to approximately 10 target molecules (or 1,000 CFU/ml BAL fluid) with PCR efficiency E of >0.94. The vapA assay had similar performance but appeared unsuitable for accurate (vapA+) R. equi quantification due to variability in target gene or plasmid copy number (1 to 9). The dual-reaction Q-PCR system here reported offers a useful tool to both medical and veterinary diagnostic laboratories for the quantitative detection of R. equi and (optional) vapA+ "horse-pathogenic" genotype determination.

Animals↗
PubMed1994

[Rhodococcus equi pneumonia in patients with immunodeficiency].

In three patients, men of 30, 21 and 24 years old respectively, Rhodococcus equi pneumonia was diagnosed. Antibiotic treatment, followed by secondary prophylaxis, was successful. In one patient, lobectomy was done. R. equi, a well-known bacterial pathogen in horses, appears also to be pathogenic in humans in case of immunodeficiency.

AIDS-Related Opportunistic Infections↗
PubMed2000

Genomic and phenomic differentiation of Rhodococcus equi and related strains.

16S rDNA sequence and pyrolysis mass spectrometric analyses were carried out on representatives of Rhodococcus equi and marker strains of genera that encompass mycolic acid containing actinomycetes. The R. equi strains formed a monophyletic clade within the evolutionary radiation occupied by members of the genera Nocardia and Rhodococcus. The 16S rDNA sequence data also showed R. equi to be an heterogeneous taxon. This heterogeneity was underscored by the pyrolysis mass spectrometric data. These observations are in line with those of previous studies where similar profiles of relatedness were found between pyrolysis mass spectral data and the results of DNA:DNA pairing and numerical phenetic studies.

Actinomycetales↗
PubMed1999

Infection by Rhodococcus equi in a patient with AIDS: histological appearance mimicking Whipple's disease and Mycobacterium avium-intracellulare infection.

Rhodococcus equi pneumonia with systemic dissemination is being reported increasingly in immunocompromised patients. This is the first case report of disseminated R equi infection with biopsy documented involvement of the large intestine. The patient was a 46 year old male with AIDS who was diagnosed with cavitating pneumonia involving the left lower lobe. R equi was isolated in culture from the blood and lung biopsies. Subsequently, the patient developed anaemia, diarrhoea, and occult blood in the stool. Colonoscopy revealed several colonic polyps. Histological examination of the colon biopsies showed extensive submucosal histiocytic infiltration with numerous Gram positive coccobacilli and PAS positive material in the histiocytes. Electron microscopy showed variably shaped intrahistiocytic organisms which were morphologically consistent with R equi in the specimen. Disseminated R equi infection may involve the lower gastrointestinal tract and produce inflammatory polyps with foamy macrophages which histologically resemble those seen in Whipple's disease and Mycobacterium avium-intracellulare infection.

AIDS-Related Opportunistic Infections↗
PubMed2006

Rhodococcus equi in the soil environment of horses in Inner Mongolia, China.

Little is known about the distribution of Rhodococcus equi in the soil environment of native horses in China. One hundred and eight soil samples were collected from native-horse farms in the Hulun Beier grasslands of eastern Mongolia, the Xilin Goler grasslands of southern Mongolia, and Tongliao City in Inner Mongolia, China. The isolation rates of R. equi from soil samples from the Hulun Beier and Xilin Goler grasslands ranged from 25.9% to 30.0%. In contrast, isolation rates from soil samples from Tongliao City were as high as 82.3% and the mean number of R. equi in soil samples from Tongliao City was 10 times more than those of samples from the grasslands. The 488 isolates were examined using PCR for the presence of genes that encode virulence-associated 15-17 kDa antigen protein (VapA) and the 20 kDa antigen protein (VapB). All isolates were negative for virulence-associated proteins. Plasmid profiles of these avirulent isolates showed that cryptic plasmids of various sizes were present with an incidence of 13.3% to 21.5%. The results of the present study contrast with those of our recent study (J. Vet. Med. Sci. 67:611-613, 2005), in which we reported that R. equi was absent from Mongolian horses in Ulaanbaatar, Mongolia. It is suggested that the difference between the results of these two studies is due to the mobile pasturing system in Mongolia and nonmobile pasturing system in Inner Mongolia.

Animals↗
PubMed1992

Immunohistochemical observations on pneumonic lesions caused by Rhodococcus equi in foals.

An immunohistochemical analysis of Rhodococcus equi-induced pneumonia in 10 foals was performed by biotin-streptavidin system. The detection of R. equi was more sensitive in immuno-stain using anti-R. equi serum than in Gram's stain. This bacteria also reacted to anti-BCG serum. Lysozyme and alpha 1-antitrypsin were detectable in macrophages. A particularly intense staining was observed in association with intracellular bacteria. Though a degree of reaction for alpha 1-antichymotrypsin was very low in comparison with lysozyme and alpha 1-antitrypsin, it was also demonstrated in macrophages ingesting R. equi. These bacteria were almost intact under an electron microscope. Therefore, the surface components of R. equi may play important roles of protection from intracellular enzymes of macrophages. The cells containing intracytoplasmic IgM, IgG or IgA were a few in number and scattered predominantly around the pneumonic lesion. It is considered that the bactericidal activity by immunoglobulins may be weak in comparison with phagocytosis by macrophages.

Actinomycetales Infections↗
PubMed1991

Selective medium containing fosfomycin, nalidixic acid, and culture supernatant of Rhodococcus equi for isolation of Corynebacterium pseudotuberculosis.

FNR medium containing fosfomycin, nalidixic acid, bovine blood and culture supernatant of Rhodococcus equi was prepared by the present authors, and the medium did not inhibit growth of Corynebacterium pseudotuberculosis but completely hampered the growth of Bacillus subtilis, Staphylococcus aureus, and Escherichia coli. The culture supernatant of R. equi facilitated detection of suspected colonies of C. pseudotuberculosis due to synergistic hemolysis. Rate of isolation of the organisms (from the trachea, larynx and nasal cavity of 16 slaughtered sheep with caseous abscess in the lung) was higher with FNR, the selective medium, than with nonselective medium. The selective medium was thus found to be useful for isolation of C. pseudotuberculosis from sheep.

Animals↗
PubMed2003

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 > or = 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.

Actinomycetales Infections↗
PubMed2003

Foal-related risk factors associated with development of Rhodococcus equi pneumonia on farms with endemic infection.

OBJECTIVE: To identify foal-related risk factors associated with development of Rhodococcus equi pneumonia among foals on farms with endemic R. equi infection. DESIGN: Prospective case-control study. ANIMALS: 220 foals at 2 equine breeding farms in Texas during a 2-year period. PROCEDURE: Information collected for each dam included age, time housed on the farm prior to parturition, whether there were any peripartum illnesses, parity, and health of previous foals. Information collected for each foal included breed, sex, gestational age, month and year of birth, location of birth, type of flooring and bedding in stall, postpartum management and preventive health care, passive immunity status, supplementation of immunoglobulins, exposure to other farms or foals affected with R. equi pneumonia, stall and pasture exposure, commingling with other mare-foal pairs, age at weaning, and whether the foal developed R. equi pneumonia. RESULTS: 32 of the 220 (15%) foals developed R. equi pneumonia, of which 4 (13%) died. Foals at 1 of the 2 farms and foals born during the second year of the study were more likely to develop R. equi pneumonia. Foal-related factors that were examined were not significantly associated with risk of R. equi pneumonia in multivariate analyses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that there are farm- and year-related effects on the risk that foals will develop R. equi pneumonia. Other foal-related factors significantly associated with R. equi pneumonia were not identified.

Actinomycetales Infections↗
PubMed2005

Virulence-associated protein-specific serum immunoglobulin G-isotype expression in young foals protected against Rhodococcus equi pneumonia by oral immunization with virulent R. equi.

The purpose of this study was to determine whether foals immunized orally from 2 days of age with virulent Rhodococcus equi developed a protective pulmonary immune response and to characterise the antibody response of the immunized foals to the virulence-associated proteins (Vaps) of the bacterium. Two groups of foals were used. One (n=4) was given live R. equi ATCC 33701 orally at 2, 7, and 14 days of age. The second group comprised three non-immunized foals age-matched to the vaccinates. At 3 weeks of age, 1 week after the final immunization, both groups were challenged intrabronchially with virulent R. equi ATCC 33701 and observed for 2 weeks post-challenge. Unvaccinated foals became clinically pneumonic and had high fever with increased heart and respiratory rates and severe pneumonia evident at necropsy. Foals of the immunized group remained healthy and lung lesions were not found post-mortem. Thus, it is possible to immunize young foals orally to protect them by 3 weeks of age against lung challenge with R. equi, even in the presence of maternal antibodies. The antibody response of the immunized foals confirmed that VapA and VapC are highly immunogenic. The immunoglobulin G isotype-related serum antibody response of immunized compared to non-immunized foals had an IgGT bias and a relatively low IgGa:IgGb ratio, both features different from what has been previously observed in immune adults and immune foals. This suggests that the serum IgG isotype profile of antibody cannot be used as a measure of evidence of protection against R. equi pneumonia.

Administration, Oral↗
PubMed1997

Rhodococcus equi pneumonia in patients infected with the human immunodeficiency virus. Report of 2 cases and review of the literature.

Rhodococcus equi is a cause of lung infection in immunosuppressed hosts. Since the start of the HIV epidemic, 76 cases of R. equi lung infection (MEDLINE 1985-96) affecting this population have been described. We report 2 additional cases and review the clinical data, radiological findings, treatment and outcome of these 78 patients. The mean age of these patients was 33 y; 69 were male. 71 met the criteria for AIDS (CDC 1993). Fever and cough were the presenting complaints in the majority of patients (84.3%). A single cavitary lung lesion in the upper lobes was the most common radiological finding (57.7%), although multiple cavitations, alveolar infiltrates and pleural effusion were also found. Treatment usually was based on synergistic antibiotic combinations for a long period of time determined on an individual basis. Surgery was performed only in 11 patients. Death attributable directly to R. equi infection is low (15.4%), however only half of the patients (53.8%) were completely cured. We conclude that R. equi infection should be strongly considered in any HIV patient who presents with cavitary lesions in the lung, especially if mycobacteria are not identified. Treatment must be based on synergistic antibiotic combinations, and surgery relegated to cases of chronic single cavitary lesions not responding to antibiotics.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Rhodococcus equi--an easily missed opportunistic pathogen.

Over the last 10 years Rhodococcus equi has been identified as an important, albeit very rare, opportunistic pathogen. As the number of patients immunocompromised from HIV infection grows, this microorganism will likely become of increasing clinical importance. Infection with R. equi is usually insidious, causing progressive pulmonary disease that is typically pleural based at the time of microbiological diagnosis. As in the case we present, the clinical and microbiological diagnoses may be significantly delayed, either by the common pitfalls encountered in the laboratory identification of R. equi, or by the failure to recognize the pathogenic potential of the isolate. R. equi infection should be suspected in immunocompromised patients with pneumonia, when a pure or predominant growth of aerobic, non-sporeforming gram-positive bacilli is found on cultures of bronchoalveolar lavage fluid and other pulmonary pathogens have been excluded.

Actinomycetales Infections↗
PubMed1997

Prevalence of the virulence-associated gene of Rhodococcus equi in isolates from infected foals.

The prevalence of the plasmid-encoded virulence-associated gene (vapA) of Rhodococcus equi, as determined by PCR, was found to be 98% in isolates from 154 foals with pneumonia, confirming the strong association of vapA with virulence. The vapA genes from 60 representative isolates were compared by digestion with the restriction endonuclease HinfI, and no evidence of sequence variation was detected.

Actinomycetales Infections↗
PubMed1998

Associations between physical examination, laboratory, and radiographic findings and outcome and subsequent racing performance of foals with Rhodococcus equi infection: 115 cases (1984-1992).

OBJECTIVE: To determine whether physical examination, laboratory, or radiographic abnormalities in foals with Rhodococcus equi infection were associated with survival, ability to race at least once after recovery, or, for foals that survived and went on to race, subsequent racing performance. DESIGN: Retrospective study. ANIMALS: 49 Thoroughbreds and 66 Standardbreds admitted to 1 of 6 veterinary teaching hospitals between 1984 and 1992 in which R equi infection was positively diagnosed. PROCEDURE: Results of physical examination, laboratory testing, and thoracic radiography were reviewed. Indices of racing performance were obtained for foals that recovered and eventually raced and compared with values for the US racing population. RESULTS: 83 (72%) foals survived. Foals that did not survive were more likely to have extreme tachycardia (heart rate > 100 beats/min), be in respiratory distress, and have severe radiographic abnormalities on thoracic radiographs at the time of initial examination than were foals that survived. Clinicopathologic abnormalities were not associated with whether foals did or did not survive. Forty-five of the 83 surviving foals (54%) eventually raced at least once, but none of the factors examined was associated with whether foals went on to race. Racing performance of foals that raced as adults was not significantly different from that of the US racing population. CLINICAL IMPLICATIONS: R equi infection in foals is associated with a decreased chance of racing as an adult; however, foals that eventually go on to race perform comparably to the US racing population.

Actinomycetales Infections↗
PubMed1993

Rhodococcus equi causing bacteremia in an adult with acute leukemia.

We have reported a case of isolated bacteremia due to Rhodococcus equi in an immunocompromised, non-HIV-infected patient with acute leukemia. This patient's illness demonstrates a rare presentation of an emerging opportunistic pathogen that may be potentially acquired via exposure to domestic horses or their habitat during periods of aggressive chemotherapeutic administration. The infection was successfully eradicated by treatment with erythromycin and rifampin. Counseling immunocompromised patients inclined to participate in recreational activities involving potential risks of exposure to this pathogen would seem to be a reasonable, but unproven, preventive intervention.

Actinomycetales Infections↗
PubMed2000

The iron dependent regulatory protein IdeR (DtxR) of Rhodococcus equi.

This paper reports the presence of an ideR gene, which encodes an iron-dependent regulatory protein, in Rhodococcus erythropolis and in the intracellular pathogen Rhodococcus equi. The ideR gene of the latter encoded a protein of 230 amino acids with a molecular mass of 25619. The alpha-helices forming the helix-turn-helix motif of the R. equi protein were identical to those of the DtxR protein of Corynebacterium diphtheriae, which is an IdeR homologue. This indicates that the two proteins bind to the same DNA binding site. This was confirmed following expression of IdeR in Escherichia coli, which showed that the IdeR protein could repress transcription of the tox promoter of C. diphtheriae in an iron dependent manner. An open reading frame specifying a 283-amino acid polypeptide similar to galE encoding UDP-galactose 4-epimerase was present downstream of the ideR gene.

Amino Acid Sequence↗
PubMedDate not supplied

Rhodococcus equi infection in patients with and without human immunodeficiency virus infection.

Rhodococcus equi is an uncommon pathogen in humans that has occasionally been reported to cause infection in individuals with impaired cellular immunity. We summarize 30 previously published reports of human infection with R. equi and describe one additional case in a patient with AIDS. Eleven (35%) of the patients discussed in this report had AIDS or human immunodeficiency virus (HIV) infection, which is emerging as the leading cause of immunosuppression in cases of R. equi infection. Seventy-seven percent of all patients had pneumonia due to R. equi, and the infiltrate frequently cavitated. When HIV-infected patients were compared with those not infected with the virus, symptoms, age, and frequency of pneumonia were similar. Sputum and blood cultures were more likely to be positive in HIV-infected patients. Individuals with HIV infection also had a higher incidence of simultaneous secondary infections and higher mortality than non-HIV-infected patients (54.5% vs. 20%). The rate of survival for all patients was 75% when antibiotics were combined with surgical resection of infected tissue; in comparison, the survival rate among patients receiving antibiotics alone was 61.1%.

Acquired Immunodeficiency Syndrome↗