Pathogenicity of Rhodococcus equi expressing a virulence-associated 20 kDa protein (VapB) in foals

Rhodococcus equi strains of intermediate virulence (IMV) for mice possess a 20kDa protein designated Virulence Associated Protein B (VapB) and a virulence plasmid of 79-100kb, and can be recovered from the submaxillary lymph nodes of pigs. The pathogenicity of such R. equi strains for foals is unknown. In this study, two foals, 42 and 43 days of age, were infected intratracheally with 10(6) and 10(9) cells of R. equi IMV strain A5, respectively. The foal infected with 10(9) cells of strain A5 became clinically ill, with the onset of illness (pyrexia and depression) occurring 21 days after inoculation. R. equi was isolated from the feces and tracheal washings of the foal from 14 to 28 days after inoculation. The foal infected with 10(6) cells of A5 showed no clinical signs, and no R. equi was isolated from any of the samples of feces or tracheal washings during the 28 days of observation. Two foals of 45 and 50 days of age were infected with 10(5) or 10(6) of virulent R. equi ATCC 33701 having 15-17kDa surface proteins designated VapA. Both exhibited severe clinical signs (pyrexia, depression and anorexia) at 12 and 13 days after inoculation. Histopathological examination revealed that strain A5 caused focal granulomatous pneumonia in the foals. R. equi IMV strain A5 was isolated from lung lesions of both foals and from the contents of the intestinal tracts of the foal infected with 10(9) bacteria. These results suggest that IMV R. equi having VapB is less virulent than virulent R. equi having VapA in foals. This finding supports our previous results on the pathogenicities of R. equi strains having these virulence-associated antigens assessed by mouse pathogenicity tests.     

Role of CD4+, CD8+ and double negative T-cells in the protection of SCID/beige mice against respiratory challenge with Rhodococcus equi.

To evaluate the contributions of T-lymphocyte subsets in pulmonary immunity against Rhodococcus equi, C.B-17 SCID/beige mice were adoptively transferred with splenic lymphocytes from congenic BALB/c mice previously infected with R. equi. Spleen cells were enriched for either CD4+ or CD8+ populations before inoculation, Flow cytometry showed that each enriched population contained less than 0.5% cross contamination. Groups of adoptively transferred SCID/beige mice were sacrificed 6 and 13 d after intranasal infection with R. equi. Bacterial clearance was measured in the lungs, liver and spleen. Lesion development was assessed by gross and histopathological score and the fate of transferred cells assessed by flow cytometry and by immunohistochemistry. SCID/beige mice receiving either CD4+ or CD8+ T-cells were able to clear the infection better than control mice. On d 6 post-infection, bacterial numbers were significantly lower in the lungs of CD4+ transferred mice as compared to CD8+ mice. By d 13, both groups had cleared R. equi from all organs. CD4+ cells were however identified in the lung and spleen of CD8+ recipients at d 13 making conclusions about the role of CD8+ cells in R. equi clearance impossible. By contrast, no significant increases in CD8+ lymphocytes were observed in the organs of CD4+ recipients. All mice developed suppurative bronchopneumonia but lesions were most severe in the CD4+ group. Immunohistochemistry and flow cytometry confirmed that CD4+ and CD8+ cells had migrated to the lungs of adoptively transferred mice. Serum antibody against R, equi was not detected by ELISA in the recipients. SCID/beige mice receiving CD4-CD8- cells were unable to clear R. equi. The study supports the suggestion that CD4+ cells have a central role in R. equi clearance in mice.     

Virulence-associated protein characterisation of Rhodococcus equi isolated from bovine lymph nodes

Rhodococcus equi has a low pathogenicity in cattle, but it occasionally causes lymph node granulomas, which are detected at abattoir post mortem inspection, and must be distinguished from tuberculous granulomas. Lymph node lesions were detected in 6719 cattle, from a total of 3,263,622 cattle examined post mortem in abattoirs, in the Republic of Ireland, during 1997 and 1998. Histological examination was performed on all lesions, principally for the purpose of identifying animals with tuberculosis. A total of 1122 of the lesions were cultured on blood agar and on Stonebrinks and Lowenstein-Jensen medium containing pyruvate, because the histological findings were difficult to interpret or were suggestive of R. equi infection. R. equi was isolated from 264 lesions. Almost all of the R. equi granulomas were confined to a single lymph node, and were present predominantly in the retropharyngeal, bronchial and mediastinal lymph nodes. R. equi granulomas were present in a significantly higher proportion of the lesions detected in steers and heifers compared to cows. The prevalence in the total population of 3.3 million cattle examined post mortem was 0.008%. The 15-17kDa antigens, associated with virulence in this organism, and the 20kDa antigen, associated with intermediate virulence, were not detected in isolates from 146 cattle, analysed by immunoblot assays. A PCR assay to detect the plasmid gene encoding the 15-17kDa antigens was also negative for isolates from these 146 animals. Plasmids were not detected in 30 isolates which were examined.     

Disseminated Rhodococcus equi infection in dromedary camels (Camelus dromedarius)

Rhodococcus (R). equi, a recognized pathogen in horses, is emerging as a human opportunistic pathogen, especially in immunocompromized people. It affects also New World camelids, but there are no reports of R. equi infection in Old World camelids yet. Four cases of disseminated R. equi infection in adult breeding dromedaries occurred at one camel farm near Dubai within 16 months of each other. At necropsy the lungs were diffusely consolidated with large caseous areas. Histology revealed severe suppurative to necrotising pneumonia with multiple encapsulated abscesses. Immunohistochemistry enabled the detection of 15- to 17-kDa antigens (VapA) of R. equi in the lung sections. High numbers of R. equi were isolated from the lung lesions as well as from liver, spleen and mediastinal lymph nodes, indicative of septicaemia. The isolated strains were PCR-positive for the specific virulence plasmid (VapA-Gen) of R. equi, indicating virulent strains and containing an 85-kb type I plasmid. This is the first report of disseminated R. equi infection in Old World camelids. Since adult camels in general do not suffer from bacterial caused pneumonia (except tuberculosis), this is a new emerging disease for camels.     

Evaluation of nasotracheal aspiration as a diagnostic tool for Rhodococcus equi pneumonia in foals

The reliability of preparing bacteriological cultures from nasotracheal aspirates of foals routinely in order to diagnose R. equi pneumonia in foals was studied by isolating Rhodococcus equi from specimens obtained from 96 foals by nasotracheal aspiration with a silicon catheter. Results were compared with specimens obtained from 21 foals by transtracheal aspiration (percutaneous tracheal puncture). These 117 foals showed clinical signs of respiratory tract infection at sampling. R. equi was isolated from 14 of 21 (66.7%) specimens by transtracheal aspiration and from 59 of 96 (61.4%) specimens by nasotracheal aspiration, 649 of 655 isolates (99.1%) from the 73 positive specimens were virulent R. equi, and the culture-positive foals were diagnosed as having R. equi pneumonia. To assess the contamination of aspirates by organisms from the nasopharynx, the results of R. equi isolation from nasal swabs obtained from 56 of the 96 foals were compared to those obtained by nasotracheal aspiration from the same foals. R. equi was isolated from 2 of the 56 nasal swabs: one from a tracheal aspirate was positive, and the other was not. These results suggest that the nasotracheal aspiration technique, which is noninvasive and not associated with complications, could be used as an alternative to the transtracheal aspiration method, especially for the diagnosis of R. equi pneumonia in foals.     

Isolation and characterisation of Rhodococcus equi from submaxillary lymph nodes of wild boars (Sus scrofa)

Rhodococcus equi has been isolated from the submaxillary lymph nodes of domesticated pigs, but little is known about the presence of R. equi in wild boars. The aim of the study was the evaluation of the incidence of R. equi in wild boars and the characterisation of them. Of 482 submaxillary lymph nodes of wild boars shot in 39 settlements throughout Hungary, R. equi was isolated from 60 specimens, and plasmid types of 82 isolates were examined. The isolates were tested for the presence of 15-17-kDa (VapA) and 20-kDa virulence-associated protein antigen (VapB) genes by polymerase chain reaction (PCR). Plasmid DNAs were isolated and analysed by digestion with restriction endonucleases to estimate size and compare their polymorphisms. None of the 82 isolates contained vapA gene but 21 isolates (25.6%) were positive for vapB gene showing 827bp product of the expected size in the PCR amplification. Sixty-one strains (74.4%) did not contain plasmid. The 21 isolates of intermediate virulence contained virulence plasmids that were identified as types 1 (1 isolate), 5 (16 isolates), 21 (1 isolate), and three new distinct plasmid variants (1-1-1 isolate), respectively. On the basis of restriction digestion patterns of plasmid DNAs, we tentatively designated the new variants as types 25-27, respectively. The prevalence of R. equi strains of intermediate virulence among the isolates originated from the submaxillary lymph nodes of wild boars (25.6%) is very similar to those of domestic pigs (26.8%) in Hungary, and plasmid type 5 is the predominating one in both groups. This is the first report of isolation of VapB-positive R. equi from wild boars in the world.     

Molecular typing of VapA-positive Rhodococcus equi isolates from Jeju native horses, Korea

We recently demonstrated the presence of virulence-associated protein antigen (VapA)-positive Rhodococcus equi in Jeju Island, Korea. These bacteria contained one of two distinct plasmid types, a 90-kb type II plasmid, which has been found in isolates from the native Kiso horses of Japan, and a new variant, a 90-kb type V plasmid. However, the genotypic characters of the VapA-positive R. equi from Jeju native horses and their environments are poorly understood. Ninety-eight isolates from soil samples and 89 isolates from fecal samples were collected from five farms that breed or have bred Jeju native horses, and were tested for the presence of VapA by immunoblotting and PCR. Of the 98 soil isolates and 89 fecal isolates, seven and 13 were VapA-positive R. equi, respectively. In 2003, two Jeju foals died suddenly and were brought to the Faculty of Veterinary Medicine, Cheju National University, for postmortem examination. Pure cultures of R. equi were isolated from the lung lesions of both foals. Of the 16 clinical isolates, 14 were VapA-positive R. equi. Of the 34 VapA-positive clinical and environmental isolates, 16 contained the 90-kb type II plasmid and 18 contained a 90-kb type V plasmid. Pulsed-field gel electrophoresis (PFGE) patterns of the VapA-positive isolates from Jeju horses and Kiso horses, containing the 90-kb type II plasmid, were compared and formed two distinct groups. Furthermore, 18 virulent isolates containing the 90-kb type V plasmid formed two distinct PFGE groups (of 16 and two isolates). These results demonstrate that two virulence plasmid types are widespread in R. equi in Jeju native horses. However, there is little diversity in the PFGE patterns of virulent isolates, suggesting the clonal spread of virulent R. equi. The PFGE pattern of the virulent R. equi isolates from Jeju native horses in Korea is not identical to those of Kiso native horses in Japan.     

Prevalence of virulent Rhodococcus equi in soil from five R. equi-endemic horse-breeding farms and restriction fragment length polymorphisms of virulence plasmids in isolates from soil and infected foals in Texas.

Rhodococcus equi isolates (462) obtained from 64 soil samples collected on 5 R. equi-endemic horse-breeding farms and isolates from 100 infected foals in Texas were examined to determine the prevalence and genotypic diversity of virulence-associated plasmids. Isolates were tested for the presence of 15-17-kDa virulence-associated protein antigens (VapA) by immunoblotting and virulence-associated plasmids by PCR. Plasmid DNAs were isolated and analyzed by digestion with restriction endonucleases for estimation of size and comparison of polymorphisims. Rhodococcus equi were isolated from soil of all 5 farms; however, virulent R. equi were only isolated from 3 of the 5 farms and represented 18.8% (87 of 462) of total isolates. Of the 87 virulent soil isolates, 56 (64.5%) contained an 85-kb type I plasmid, 23 (26.4%) an 87-kb type I plasmid, 7 (8%) a newly defined 85-kb type III plasmid (Tx 43), and 1 (1.1%) a newly defined 85-kb type IV plasmid (Tx 47). Of the 100 isolates from infected foals, 96 were virulent. Of the 96 virulent isolates, 51 (53.1%) contained an 85-kb type I plasmid, 39 (40.6%) an 87-kb type I plasmid, 4 (4.2%) an 85-kb type III plasmid (Tx 43), and 2 (2.1%) an 85-kb type IV plasmid (Tx 47). There are at least 4 different R. equi virulence-associated plasmids in Texas, 2 of which have not previously been described. Based upon virulence plasmid typing, there is geographic diversity among isolates of R. equi from clinical and environmental samples on horse-breeding farms in Texas. There is not a strong correlation between the presence of virulent R. equi in farm soils and the R. equi disease status of those farms.     

Comparison of two selective media for the recovery, isolation, enumeration and differentiation of Rhodococcus equi

The use of selective media to facilitate the isolation of Rhodococcus equi from environmental and clinical samples has aided studies of the ecology of R. equi and the epidemiology of disease caused by R. equi. Here, we compared the efficacy of two selective media (NANAT and modified CAZ-NB) for the recovery of six defined strains of R. equi and for the isolation and enumeration of both avirulent and virulent R. equi from 60 paired soil samples from horse farms using colony blotting and DNA hybridisation. No difference was found between the two media in the recoverability of defined strains of R. equi or the proportion of soil cultures positive for R. equi or virulent R. equi. NANAT medium was significantly less inhibitory of bacterial growth from soil culture compared to mCAZ-NB (P = 0.001), but there was no difference between the media in the number of R. equi colonies recovered. Soil cultured on mCAZ-NB medium yielded a significantly greater number of virulent R. equi colonies than NANAT (P = 0.03). The proportion of R. equi that were virulent in soil cultures on mCAZ-NB (32%) was more than three times that seen in cultures on NANAT (9%). Thus modified CAZ-NB appeared to be a better selective media for studies where the optimal recovery of virulent R. equi is required, such as in studies of the gastrointestinal carriage of virulent R. equi and of subclinically infected foals.     

Prevalence of virulent Rhodococcus equi in isolates from soil collected from two horse farms in South Africa and restriction fragment length polymorphisms of virulence plasmids in the isolates from infected foals, a dog and a monkey

The prevalence of virulent Rhodococcus equi in soil isolates from two horse farms in South Africa and nine clinical isolates from six foals, a foal foetus, a dog, and a monkey was investigated. The isolates were tested for the presence of virulence plasmid DNA and 15- to 17-kDa antigens by immunoblotting. Rhodococcus equi was isolated from almost all of the soil samples obtained from the two farms with 5.0 x 10(1) to 3.3 x 10(4) colony forming units per gram of soil. Virulent R. equi was isolated from three soil samples from one of the farms and appeared in 3.8% (three of 80 isolates), but not in any of the 182 isolates from the other farm. Of the three virulent R. equi isolates, one contained an 85-kb type I plasmid and two an 87-kb type I plasmid. Of nine clinical isolates from the foals, foal foetus, dog and monkey, five from the foals were virulent R. equi which expressed the virulence-associated antigens and contained a virulence plasmid 85-kb type I, and were all isolated from cases of pneumonia typical of that induced by R. equi in young foals living in widely separated areas in South Africa. The isolates from the other four foals, the dog and the monkey were avirulent R. equi.     

Evaluation of a multiplex polymerase chain reaction assay for simultaneous detection of Rhodococcus equi and the vapA gene

OBJECTIVE: To evaluate sensitivity and specificity of a multiplex polymerase chain reaction (PCR) assay for simultaneous detection of Rhodococcus equi and differentiation of strains that contain the virulence-associated gene (vapA) from strains that do not. SAMPLE POPULATION: 187 isolates of R equi from equine and nonequine tissue and environmental specimens and 27 isolates of bacterial species genetically or morphologically similar to R equi. PROCEDURE: The multiplex PCR assay included 3 gene targets: a universal 311-bp bacterial 16S ribosomal RNA amplicon (positive internal control), a 959-bp R equi-specific target in the cholesterol oxidase gene (choE), and a 564-bp amplicon of the vapA gene. Duplicate multiplex PCR assays for these targets and confirmatory singleplex PCR assays for vapA and choE were performed for each R equi isolate. An additional PCR assay was used to examine isolates for the vapB gene. RESULTS: Results of duplicate multiplex and singleplex PCR assays were correlated in all instances, revealing high specificity and reliability (reproducibility) of the vapA multiplex assay. Of the pulmonary isolates from horses with suspected R equi pneumonia, 97.4% (76/78) yielded positive results for vapA. Seven of 50 (14%) human isolates of R equi yielded positive results for vapA. Six human R equi isolates and 1 porcine isolate yielded positive results for vapB. No isolates with vapA and vapB genes were detected. CONCLUSIONS AND CLINICAL RELEVANCE: The multiplex PCR assay is a sensitive and specific method for simultaneous confirmation of species identity and detection of the vapA gene. The assay appeared to be a useful tool for microbiologic and epidemiologic diagnosis and research.     

Development of a live, attenuated, potential vaccine strain of R. equi expressing vapA and the virR operon, and virulence assessment in the mouse

Pneumonia caused by Rhodococcus equi remains a significant problem in foals. The objective of this study was to develop a safe and efficacious attenuated strain of R. equi for eventual use in oral immunization of foals. The approach involved expression of vapA in a live, virulence plasmid-negative, strain of R. equi (strain 103-). PCR-amplified fragments of the vapA gene, with and without the upstream genes virR, orf5, vapH, orf7 and orf8 (orf4-8), were cloned into a shuttle vector pNBV1. These plasmids, named pAW48A and pAWVapA respectively, were electroporated into strain 103-. The presence of the recombinant vectors in the attenuated strain (103-) and the integrity of the inserted genes were confirmed, and both constructs expressed VapA. The virulence of the two strains was compared to that of wild type R. equi 103+ and negative controls by their intravenous inoculation into mice, followed by examination of liver clearance 4 days later. Mice inoculated with R. equi 103-, 103-/pAWVapA and 103-/pNBV1 completely cleared infection, whereas strain 103-/pAW48A persisted in 47% of mice.     

Association of disease with isolation and virulence of Rhodococcus equi from farm soil and foals with pneumonia

OBJECTIVE: To determine whether isolation and virulence of Rhodococcus equi from soil and infected foals are associated with clinical disease. DESIGN: Cross-sectional and case-control study. SAMPLE POPULATION: R equi isolates from 50 foals with pneumonia and soil samples from 33 farms with and 33 farms without a history of R equi infection (affected and control, respectively). PROCEDURE: R equi was selectively isolated from soil samples. Soil and clinical isolates were evaluated for virulence-associated protein antigen plasmids (VapA-P) and resistance to the beta-lactam antibiotics penicillin G and cephalothin. Microbiologic cultures and VapA-P assays were performed at 2 independent laboratories. RESULTS: VapA-P was detected in 49 of 50 (98%) clinical isolates; there was complete agreement between laboratories. Rhodococcus equi was isolated from soil on 28 of 33 (84.8%) affected farms and 24 of 33 (72.7%) control farms, but there was poor agreement between laboratories. Virulence-associated protein antigen plasmids were detected on 14 of 66 (21.2%) farms by either laboratory, but results agreed for only 1 of the 14 VapA-P-positive farms. We did not detect significant associations between disease status and isolation of R equi from soil, detection of VapA-P in soil isolates, or resistance of soil isolates to beta-lactam antibiotics. No association between beta-lactam antibiotic resistance and presence of VapA-P was detected. CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of soil microbiologic culture and VapA-P assay results, it is not possible to determine whether foals on a given farm are at increased risk of developing disease caused by R equi.     

Chemoprophylactic effects of azithromycin against Rhodococcus equi-induced pneumonia among foals at equine breeding farms with endemic infections

OBJECTIVE: To determine the effect of azithromycin chemoprophylaxis on the cumulative incidence of pneumonia caused by Rhodococcus equi, age at onset of pneumonia, and minimum inhibitory concentration (MIC) of azithromycin for R equi isolates cultured from fecal and clinical samples. DESIGN: Controlled, randomized clinical trial. ANIMALS: 338 foals born and raised at 10 equine breeding farms; each farm had a history of endemic R equi infections. PROCEDURES: Group 1 foals were control foals, and group 2 foals were treated with azithromycin (10 mg/kg [4.5 mg/lb], PO, q 48 h) during the first 2 weeks after birth. Foals were monitored for development of pneumonia attributable to R equi infection and for adverse effects of azithromycin. Isolates of R equi were tested for susceptibility to azithromycin. RESULTS: The proportion of R equi-affected foals was significantly higher for control foals (20.8%) than for azithromycin-treated foals (5.3%). Adverse effects of azithromycin treatment were not detected, and there were no significant differences between groups for the MICs of azithromycin for R equi isolates cultured from fecal or clinical samples. CONCLUSIONS AND CLINICAL RELEVANCE: Azithromycin chemoprophylaxis effectively reduced the cumulative incidence of pneumonia attributable to R equi among foals at breeding farms with endemic R equi infections. There was no evidence of resistance to azithromycin. Nonetheless, caution must be used because it is possible that resistance could develop with widespread use of azithromycin as a preventative treatment. Further investigation is needed before azithromycin chemoprophylaxis can be recommended for control of R equi infections.     

The effect of immunosuppression on resistance to Rhodococcus equi in mice

Rhodococcus equi, a natural pathogen of horses, produces lesions in mice following experimental infection. The effect of various immunosuppressing agents on the sequential development of these lesions has been assessed by measuring the growth of R. equi following intravenous or intranasal challenge and by histological examination. Cyclophosphamide treatment of mice, challenged intranasally, resulted in the development of lesions not unlike that seen in experimental and natural infection in foals. Cortisone acetate also impaired bacterial clearance from the lungs and affected the accumulation of mononuclear cells at infective foci. Most of the agents chosen to impair macrophage function failed to affect the resistance of mice to R. equi. Carbon, carrageenan and silica failed to alter significantly the growth kinetics of R. equi. Dextran sulphate depressed the rate of pulmonary clearance of organisms and affected the ability of animals to eliminate R. equi following rechallenge. Overall, these results support other evidence that cell mediated immunity is involved in host resistance to R. equi and that activated macrophages play a role in acquired immunity to this organism.     

Experimental infection of piglets by aerosols of Rhodococcus equi.

The purpose of this study was to investigate experimental infection of the piglet as a model of Rhodococcus equi pneumonia in the foal. Three litters of eight piglets each were exposed to an aerosol of 3.4 X 10(7) R. equi per piglet per day for seven consecutive days. Over the next 23 days the piglets were observed for clinical signs of disease. Periodically after infection one piglet from each litter was killed, the lungs were cultured quantitatively for R. equi and the gross and microscopic pulmonary lesions were assessed. The only clinical evidence of disease was the occurrence of elevated temperatures in the infected piglets. Rhodococcus equi was slowly cleared from the piglets' lungs during the 23 days following aerosolization. Piglets sacrificed seven to ten days after aerosolization had the most extensive pulmonary lesions, consisting of severe consolidation of the cranioventral lobes. Microscopic examination revealed thickened interalveolar septa and alveoli containing many neutrophils and macrophages with intracytoplasmic Gram-positive coccobacilli. The pulmonary lesions in these piglets differed from those of naturally infected foals in that they were not characterized by macrophage-rich abscesses and the infection gradually resolved.     

Characterization of virulence plasmid types in Rhodococcus equi isolates from foals,pigs, humans and soil in Hungary

Rhodococcus equi isolates (204) obtained from foals (lung abscesses, lymph nodes, nasal discharge, rectal swabs) bred in 15 studs located throughout Hungary, isolates from soil samples, lymph nodes of pigs and from lesions of human patients were examined to determine genotypic diversity of virulence-associated plasmids. Isolates were tested for the presence of 15-17 kDa virulence-associated protein antigen (VapA) and 20k Da (VapB) genes by polymerase chain reaction (PCR). Plasmid DNAs were isolated and analysed by digestion with restriction endonucleases for estimation of size and comparison of polymorphisms. Of 146 clinical isolates from foals in 15 studs, 129 (88.3%) gave positive results for the VapA gene, showing a 564 bp product of the expected size in the PCR amplification. Of the 129 clinical isolates from foals, 123 contained an 85 kb type I plasmid and the remaining six contained an 87 kb type I plasmid. Of 48 soil isolates from two horse studs, 26 (54.2%) were positive for VapA gene and contained an 85 kb type I plasmid. Of three pig isolates, one was positive for VapA gene and contained an 85 kb type I plasmid, and the remaining two were positive for the VapB gene, showing a 827 bp product of the expected size in the PCR amplification and were R. equi of intermediate virulence which contained a 95 kb type S5 plasmid. Of the seven human isolates, five were positive for VapB gene by PCR, these were R. equi of intermediate virulence, which contained a 95 kb type S5 plasmid. These results revealed that virulent R. equi strains harbouring a virulence plasmid of 85 kb type I or 87 kb type I, which have been found in clinical isolates from Europe and North and South America, are widespread in Hungary. Furthermore, same intermediately virulence plasmid type was found in both human and pig isolates.     

Rhodococcus equi infection of cats

Six cases of Rhodococcus equi infection in cats are described. One cat had pneumonia and died. The remaining five cats had cutaneous lesions affecting the feet in four of the cats and the metacarpus in one cat, and all these cats recovered with the aid of antibiotics. All the Rhodococcus equi isolates were sensitive to amoxycillin/clavulanic acid and, where used, at least 14–16 days of treatment was needed to help eliminate the infection. Histologically and cytologically the reaction was pyogranulomatous and many macrophages in the lesions contained large numbers of Gram-positive bacteria.     

Clinical evaluation of the serodiagnostic value of enzyme-linked immunosorbent assay for Rhodococcus equi infection in foals

An enzyme-linked immunosorbent assay (ELISA) for detection of serum IgG antibodies against Tween 20-extracted antigen of strain ATCC 6939 was applied in Hidaka, Japan to a total of 752 sick foals showing a variety of signs of infectious disease. An optical density (OD) value of more than 0.3 was tentatively fixed to be positive on the basis of readings made of healthy horse sera in previous studies. During a 2 year study, 138 of the 752 sick foals showed an OD value of 0.3 or higher and were designated as 'suspected of R. equi infection'. Age distribution during the initial medical examination of the 138 seropositive foals was significant in that most (64%) foals were age 31-60 days, with a sharp decrease in subjects beyond that age. Of the 138 foals suspected of having R. equi infection, 34 foals (25%) showed OD values of over 0.9 at the initial medical examination, in addition to high blood leucocyte counts and serum fibrinogen and alpha-globulin values. The infectious foals had been treated with antibiotics just before and after serodiagnosis and 126 foals (91%) recovered from the disease. However, no clinical improvement was observed in 12 foals (9%). At necropsy, these foals revealed suppurative pneumonia and lymphadenitis of gut associated lymph nodes accompanied by abdominal abscesses. All isolates from the pulmonary and abdominal abscesses revealed R. equi. These results suggest that OD readings in the high range are associated with severe disseminated infection with R. equi.