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1.
Rhodococcus equi (R equi) pneumonia is an important cause of disease and death in foals. Feces from mares can contain R equi, including virulent R equi, and thus may act as a source of the bacteria at horse breeding farms. A previous report documented that every mare at a farm in central Kentucky shed virulent R equi in at least one of four fecal samples collected serially during the periparturient period. The objective of this study was to assess the extent to which this high prevalence of fecal shedding could be replicated at other horse breeding farms. The frequency of detection of R equi and virulent R equi in fecal samples was studied among 131 mares from 24 farms in central Kentucky. The proportions of fecal samples from mares containing R equi and virulent R equi were 95% and 76%, respectively. These findings indicate that R equi and virulent R equi may be isolated with high frequency from feces of mares at breeding farms in central Kentucky, and that mares are a source of virulent R equi for the environment of their foals.  相似文献   

2.
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.  相似文献   

3.
The aim of this study was to evaluate the usefulness of the previously identified B‐cell epitope TSLNLQKDEPNGRASDTAGQ of the VapA protein of Rhodococcus equi and its association with R. equi pneumonia. A modified peptide designated PN11‐14 corresponding to the epitope was recognized by all sera from experimentally infected foals with virulent R. equi ATCC103+ containing the virulence plasmid but not by its plasmid‐cured derivative ATCC103? strain. Marked levels of VapA‐specific immunoglobulin (Ig)G were detected in all sera from the ATCC103+ infected foals at 2 weeks after the infection. One control animal had high titres as determined by the peptide enzyme‐linked immunosorbent assay (ELISA), indicating the ELISA may not absolutely differentiate between foals with R. equi pneumonia and healthy exposed foals in farms where the prevalence of disease is high. However, numbers of animals used were small. Further evaluation of the peptide ELISA with field samples is necessary to determine whether the assay is diagnostically useful. This study showed that levels of passive transfer of maternal IgG antibodies to the epitope in newborn foals could be measured. Interestingly, the maternally derived antibodies were found to significantly (P < 0.05 by Student's t‐test) decline 2 weeks after birth. Seroconversion against naturally occurring VapA expressing R. equi could be detected in some foals at 4 weeks of age. Antibodies to the epitope peaked and were significantly (P < 0.05) greater in foals aged between 6 and 8 weeks. These results indicated that the peptide ELISA could be used to monitor anti‐VapA antibodies in foals, particularly those at the age of 4–6 weeks. It is possible that the ELISA may be of some use as a diagnostic test on farms where R. equi is non‐endemic. Further studies using large number of field samples are needed to verify this assumption.  相似文献   

4.
Early diagnosis and prevention of Rhodococcus equi pneumonia in foals represent important goals for equine clinicians. Recent protocols for diagnosis and treatment of Rhodococcosis in foals typically rely on a multimodal approach based on sonographic evidence suggestive of pyogranulomas, sonographic abscess scores and laboratory findings including plasma fibrinogen concentrations, blood biochemistry testing and platelet and leukocyte counts. The aim of this study was to assess the utility of weekly testing of serum amyloid A (SAA) and plasma fibrinogen concentrations in foals to achieve early diagnosis of R. equi pneumonia prior to the onset of clinical signs. This testing was used to simulate a clinically practical screening procedure and compared with thoracic ultrasonography performed in parallel.The present study suggests that SAA does not represent a reliable early marker of Rhodococcosis when plasma concentrations are tested weekly. However, when clinical signs of R. equi pneumonia are present, SAA concentrations may allow clinicians to obtain ‘real-time’ indications concerning both the progress of infection and the effectiveness of therapy. This study raises the possibility that plasma fibrinogen monitoring starting at 1 week of age and repeated on a weekly basis, could serve as a screening test allowing clinicians to identify foals as suspected of R. equi infection. Future investigations regarding both physiological plasma fibrinogen concentrations in foals as well as fibrinogen kinetics in foals affected with R. equi pneumonia, including the establishment of appropriate reference intervals for the test method employed in this study, will be necessary in order to clarify this possibility.  相似文献   

5.
Rhodococcus equi pneumonia is a worldwide infectious disease of major concern to the equine breeding industry. The disease typically manifests in foals as pyogranulomatous bronchopneumonia, resulting in significant morbidity and mortality. Inhalation of aerosolised virulent R. equi from the environment and intracellular replication within alveolar macrophages are essential components of the pathogenesis of R. equi pneumonia in the foal. Recently documented evidence of airborne transmission between foals indicates the potential for an alternative contagious route of disease transmission. In the first of this two-part review, the complexity of the host, pathogen and environmental interactions that underpin R. equi pneumonia will be discussed through an exploration of current understanding of the epidemiology and pathogenesis of R. equi pneumonia in the foal.  相似文献   

6.
SUMMARY A trial was conducted on a Thoroughbred stud to determine whether or not the administration of anti-Rhodococcus equi hyperimmune plasma would reduce the prevalence of R equi pneumonia (rattles) in foals born in the 1992 horse breeding season. Hyperimmune plasma was administered to 34 foals; another 57 foals were untreated. There was no significant difference in the number of transfused foals developing R equi pneumonia compared with the untreated foals. The time required for recovery from pneumonia between the 2 groups was not significantly different.  相似文献   

7.
Rhodococcus equi is an intracellular pathogen of macrophages that causes rhodococcal pneumonia in foals and immunocompromised people. Evidence exists that neutrophils play a vital role in resistance to infection with R. equi; however, the means by which neutrophils exert their effects have not been clearly defined. In addition to directly killing bacteria, neutrophils also may exert a protective effect by linking innate and adaptive immune responses. In the present study we evaluated the cytokine expression profiles of adult equine neutrophils in response to stimulation with isogenic strains of virulent and avirulent R. equi in vitro. After 2 and 4 h incubation with virulent or avirulent R. equi, adult equine neutrophils expressed significantly (P < 0.05) greater tumor necrosis factor alpha (TNFα), interleukin (IL)-12p40, IL-6, IL-8 and IL-23p19 mRNA, but not interferon gamma (IFNγ) or IL-12p35 mRNA than unstimulated neutrophils. Furthermore, virulent R. equi induced significantly greater IL-23p19 mRNA than avirulent R. equi. These results demonstrate that R. equi-stimulated neutrophils are a source of many proinflammatory cytokines. Furthermore, these results suggest that IL-23 may be preferentially expressed over IL-12 in response to exposure with R. equi, and that this response may be more strongly induced by virulent R. equi than avirulent R. equi. Collectively, the data presented herein suggest a non-phagocytic role for neutrophils that may influence the type of adaptive immune response to R. equi.  相似文献   

8.
There is a distinct age-associated susceptibility of horses to Rhodococcus equi infection. Initial infection is thought to occur in the neonatal and perinatal period, and only foals less than 6 months of age are typically affected. R. equi is closely related and structurally similar to Mycobacterium tuberculosis, and causes similar pathologic lesions. Protective immune responses to M. tuberculosis involve classical major histocompatibility complex (MHC)-restricted T cells that recognize peptide antigen, as well as MHC-independent T cells that recognize mycobacterial lipid antigen presented by CD1 molecules. Given the structural similarity between these two pathogens and our previous observations regarding R. equi-specific, MHC-unrestricted cytotoxic T lymphocytes (CTL), we developed 3 related hypotheses: (1) CD1 molecules are expressed on equine antigen presenting cells (APC), (2) CD1 expression on APC is less in foals compared to adults and (3) infection with live virulent R. equi induces up-regulation of CD1 on both adult and perinatal APC. CD1 expression was examined by flow cytometric analysis using a panel of monoclonal CD1 antibodies with different species and isoform specificities.

Results

Three CD1 antibodies specific for CD1b showed consistent cross reactivity with both foal and adult monocyte-derived macrophages (MDM). CD1b and MHC class II expression were significantly higher on adult MDM compared with foals. R. equi infected MDM showed significantly lower expression of CD1b, suggesting that infection with this bacterium induces down-regulation of CD1b on the cell surface. Histograms from dual antibody staining of peripheral blood mononuclear cells also revealed that 45–71% of the monocyte population stained positive for CD1b, and that the majority of these also co-expressed MHC II molecules, indicating that they were APC. The anti-CD1 antibodies showed no binding or minimal binding to bronchoalveolar lavage (BAL)-derived macrophages.

Conclusion

The CD1b isoform is evolutionarily conserved, and is present on equine MDM, as well as on circulating blood monocytes. The unique susceptibility of foals to R. equi infection may be due in part to lower expression of CD1 and MHC class II, as observed in this study. The data also suggests that infection with R. equi induces down-regulation of CD1b on equine MDM. This may represent a novel mechanism by R. equi to avoid detection and killing of infected cells by the immune system, similar to that observed when human APC are infected with M. tuberculosis.  相似文献   

9.
OBJECTIVE: To identify farm characteristics and management practices associated with development of Rhodococcus equi pneumonia in foals. DESIGN: Prospective case-control study. ANIMALS: 5230 foals on 138 breeding farms with 9136 horses. PROCEDURE: During 2003, participating veterinarians provided data from 1 or 2 farms with > or =1 foal with R equi pneumonia and unaffected farms. Data from affected and unaffected farms were compared by use of logistic regression analysis. RESULTS: A number of variables relating to farm size and desirable management practices were significantly associated with increased odds of farms being affected with R equi pneumonia. By use of multivariate logistic regression, affected farms were determined significantly more likely to have raised Thoroughbreds, housed > or =15 foals, used concrete floors in foaling stalls, and tested foals for passive transfer of immunity than unaffected farms. These results remained significant even after accounting for exposure of foals to other breeding farms during the first month of life. Conclusions and Clinical Relevance-Breeding farms with large acreage and a large number of mares and foals have greater odds of being affected by R equi pneumonia. Clinical relevance of associations with Thoroughbred breed and concrete flooring in foaling stalls remains uncertain. Desirable management factors commonly used on farms were not effective for controlling or preventing development of R equi pneumonia. This finding indicates a need to focus on host factors that influence disease development.  相似文献   

10.
OBJECTIVE: To determine whether foal management practices, environmental management, and preventative health practices are risk factors for development of Rhodococcus equi pneumonia in foals. DESIGN: Prospective matched case-control study. ANIMALS: 2,764 foals on 64 equine breeding farms with 9,991 horses. PROCEDURE: During 1997, participating veterinarians completed paired data collection forms for comparison; 1 for an affected farm (containing > or = 1 foal with pneumonia caused by R equi) and 1 for a control farm. Information collected pertained to stabling facilities, environmental management, foal husbandry, and preventative equine health practices. RESULTS: Matched farm data compared by use of conditional logistic regression indicated that personnel on affected farms were more likely to attend foal births, test foals for adequacy of passive immunity, administer plasma or other treatments to foals to supplement serum immunoglobulin concentrations, administer hyperimmune plasma prophylactically to foals, vaccinate mares and foals against Streptococcus equi infection, and use multiple anthelmintics in deworming programs. Affected farms were also more likely to have foals that developed other respiratory tract disorders and were approximately 4 times as likely to have dirt floors in stalls used for housing foals as were control farms. CONCLUSIONS AND CLINICAL RELEVANCE: Rhodococcus equi pneumonia does not appear to be associated with poor farm management or a lack of attention to preventative health practices. Housing foals in stalls with dirt floors may increase the risk for development of R equi pneumonia.  相似文献   

11.
The objective of this pilot study was to compare the cytokine profile as well as cell-mediated and antibody responses of foals infected with a low inoculum of virulent Rhodococcus equi resulting in subclinical pneumonia to that of foals infected with a high inoculum resulting in severe clinical pneumonia. The mean (±SD) ratio of post-infection to pre-infection anti-R. equi IgG(T) concentration was significantly (P = 0.002) higher in foals infected with the high inoculum (195 ± 145; range 62–328) compared to foals infected with the low inoculum (3.9 ± 4.5; range 0.5–11). Similarly, mean (±SD) ratio of post-infection to pre-infection IgM concentration was significantly (P = 0.002) higher in foals infected with the high inoculum (12 ± 4.0; range 7.4–14) compared to foals infected with the low inoculum (2.5 ± 1.5; range 1.2–4.7). Proliferative responses to R. equi antigens as well as expression of mRNA for IL-2, IL-4, IL-10, and IFN-γ in BLN were not significantly different between the two groups. There was a tendency (P = 0.073) towards a higher IFN-γ/IL-4 ratio in the low inoculum group. This study demonstrates that the size of inoculum modulates the IgG subisotype response and possibly the cytokine profile of foals.  相似文献   

12.
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.  相似文献   

13.
OBJECTIVE: To determine whether soil concentrations of total or virulent Rhodococcus equi differed among breeding farms with and without foals with pneumonia caused by R equi. SAMPLE POPULATION: 37 farms in central Kentucky. Procedures-During January, March, and July 2006, the total concentration of R equi and concentration of virulent R equi were determined by use of quantitative bacteriologic culture and a colony immunoblot technique, respectively, in soil specimens obtained from farms. Differences in concentrations and proportion of virulent isolates within and among time points were compared among farms. RESULTS: Soil concentrations of total or virulent R equi did not vary among farms at any time point. Virulent R equi were identified in soil samples from all farms. Greater density of mares and foals was significantly associated with farms having foals with pneumonia attributable to R equi. Among farms with affected foals, there was a significant association of increased incidence of pneumonia attributable to R equi with an increase in the proportion of virulent bacteria between samples collected in March and July. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that virulent R equi were commonly recovered from soil of horse breeding farms in central Kentucky, regardless of the status of foals with pneumonia attributable to R equi on each farm. The incidence of foals with pneumonia attributable to R equi can be expected to be higher at farms with a greater density of mares and foals.  相似文献   

14.
Pneumonia in foals caused by the bacterium Rhodococcus equi has a worldwide distribution and is a common cause of disease and death for foals. The purpose of this narrative review was to summarise recent developments pertaining to the epidemiology, immune responses, treatment, and prevention of rhodococcal pneumonia of foals. Screening tests have been used to implement earlier detection and treatment of foals with presumed subclinical R. equi pneumonia to reduce mortality and severity of disease. Unfortunately, this practice has been linked to the emergence of antimicrobial-resistant R. equi in North America. Correlates of protective immunity for R. equi infections of foals remain elusive, but recent evidence indicates that innate immune responses are important both for mediating killing and orchestrating adaptive immune responses. A macrolide antimicrobial in combination with rifampin remains the recommended treatment for foals with R. equi pneumonia. Great need exists to identify which antimicrobial combination is most effective for treating foals with R. equi pneumonia and to limit emergence of antimicrobial-resistant strains. In the absence of an effective vaccine against R. equi, passive immunisation remains the only commercially available method for effectively reducing the incidence of R. equi pneumonia. Because passive immunisation is expensive, labour-intensive and carries risks for foals, great need exists to develop alternative approaches for passive and active immunisation.  相似文献   

15.
A molecular epidemiological survey of the protozoal parasites that cause equine piroplasmosis was conducted using samples collected from horses and zebra from different geographical locations in South Africa. A total of 488 samples were tested for the presence of Theileria equi and/or Babesia caballi using the reverse line blot hybridization assay. Ten percent of the samples hybridized to the Theileria/Babesia genus-specific probe and not to the B. caballi or T. equi species-specific probes, suggesting the presence of a novel species or genotype. The small subunit of rRNA gene (18S; ∼1600 bp) was amplified and sequenced from 33 of these 488 samples. Sequences were compared with published sequences from the public sequence databases. Twelve distinct T. equi and six B. caballi 18S rRNA sequences were identified. Alignments demonstrated extensive sequence variation in the V4 hypervariable region of the 18S rRNA gene within T. equi. Sequence variation was also found in B. caballi 18S rRNA genes, although there was less variation than observed for T. equi. Phylogenetic analysis based on 18S rRNA gene sequences revealed three T. equi clades and two B. caballi clades in South Africa. The extent of sequence heterogeneity detected within T. equi and B. caballi 18S rRNA genes was unexpected since concerted evolution is thought to maintain homogeneity within repeated gene families, including rRNA genes, in eukaryotes. The findings reported here show that careful examination of variants of the 18S rRNA gene of T. equi and B. caballi is required prior to the development of molecular diagnostic tests to detect these parasites in horses. Species-specific probes must be in designed in regions of the gene that are both conserved within and unique to each species.  相似文献   

16.
Objective – To describe the clinical presentation, case management, and outcome in 2 foals with Rhodococcus equi infection associated with presumptive severe immune‐mediated hemolytic anemia. Series Summary – Two foals diagnosed with R. equi pneumonia on the basis of tracheal wash cultures, thoracic radiographs, and thoracic ultrasonography were concurrently diagnosed with hemolytic anemia. Both foals required whole blood transfusions, and were treated with the antimicrobial combination of rifampin and a macrolide (eg, clarithromycin, erythromycin, or azithromycin). Dexamethasone was used to prevent further hemolysis in both foals, and to treat acute lung injury/acute respiratory distress syndrome in 1 of the foals. Both foals survived, and required prolonged antimicrobial therapy. New or Unique Information Provided – Although extra‐pulmonary disorders are commonly diagnosed in foals infected with R. equi, hemolytic anemia is rarely described. Dexamethasone is considered the treatment of choice for immune‐mediated hemolytic anemia, but may be contra‐indicated in foals with severe bacterial infections. In these foals, a relatively low dose and short duration of dexamethasone was utilized in an attempt to minimize immune suppression, although early discontinuation in 1 foal precipitated a second hemolytic crisis.  相似文献   

17.
Four month-old foals were infected orally with 75 mL of a suspension of 5.0 × 108 Corynebacterium equi per mL. Two foals were killed after ten days and had scanty number of C. equi in the caeco-colic lymph nodes. No C. equi were recovered from the other two foals, killed 20 days after infection. No gross pathological change was detected in these four foals, although mild microscopic lesions were seen in the ileum of one foal. Results of lymphocyte blastogenesis using peripheral blood lymphocytes and C. equi antigens showed, however, that lymphocytes became sensitized to C. equi following this challenge.

In a second experiment four month-old foals were given orally the same dose of organisms but on five consecutive days. Two foals were killed ten days after infection and showed mild histological changes in the large bowel mucosa and C. equi could be recovered from all intestinal lymph nodes cultured. In one of these foals moderate numbers of C. equi were present in the bronchial lymph node. Of the other two foals, one died after 22 days with severe ulcerative enterocolitis and intestinal lymphadenitis. Only one small pulmonary abscess was detected despite large numbers of C. equi in the lungs. The other foal developed similar intestinal changes and was euthanized 25 days after infection. No C. equi were detected in the lungs or bronchial lymph node. Lymphocyte blastogenesis in these animals showed a rapid rise in response to C. equi antigens.

These studies suggest that C. equi pneumonia in foals does not always arise from an intestinal infection, that minor intestinal infection causes a cellular immune response and that massive exposure of the bowel over a sustained period is necessary to induce intestinal lesions.

  相似文献   

18.
A relative immunodeficiency of young foals is considered to account for the increased susceptibility of foals to infectious diseases, including pneumonia caused by Rhodococcus equi. In this report, peripheral blood mononuclear cells (PBMCs) from healthy foals at 14 and 56 days of age, or from their dams, were incubated with three stimulatory and one nonstimulatory (control) synthetic cytosine-phosphate-guanosine oligodeoxynucleotides (CpG-ODNs), and mRNA expression of tumor necrosis factor alpha (TNF-α), interferon gamma (IFN-γ), interleukin (IL) -6, IL-8, IL12-p35, and IL-12p40 were determined. Results indicated that synthetic CpG-ODNs can induce strong, rapid cytokine responses in healthy foals and adult horses. B-class CpG-ODNs 2135 and 2142 induced greater messenger RNA (mRNA) expression of IFN-γ, IL-6, and IL-12p40 than the C-class CpG-ODN 2395 in foal PBMCs. In foals, B-class CpG-ODNs induced IFN-γ, IL-6, and IL-12P40 mRNA expression that was similar to or higher in magnitude than that observed in adult horses. These observations indicate that CpG-ODNs might be useful as immunomodulators or as potential adjuvants for vaccines to aid in preventing R. equi pneumonia and other bacterial diseases of foals.  相似文献   

19.
REASONS FOR PERFORMING STUDY: Rhodococcoccus equi is a significant cause of bronchopneumonia in foals worldwide. Infection of the lungs is believed to result from inhalation of virulent R. equi in dust from contaminated environments. A measure of infectious risk in an environment is the level of airborne contamination. OBJECTIVES: To assess and compare the level of airborne virulent R. equi in paddocks and stables. METHODS: Air samples were collected sequentially over the 2003 foaling season from the paddocks and stables on 3 Irish horse breeding farms affected by R. equi pneumonia. Colony blotting and DNA hybridisation techniques allowed quantitation of virulent R. equi. RESULTS: The odds of detecting airborne virulent R. equi in stables were 173 times greater than in paddocks. The median airborne concentration of virulent R. equi was significantly higher (P < 0.001) in stables than in paddocks on all farms. These observations suggested that stables were high-risk areas for infection. CONCLUSIONS AND POTENTIAL RELEVANCE: Our results indicate that contaminated stables are a significant risk factor in the epidemiology of R. equi pneumonia on horse-breeding farms in a temperate climate, such as in Ireland. Management strategies that improve the air hygiene of stables, through better ventilation, use of less fragile bedding material and the use of fogging agents to reduce the airborne concentration of virulent R. equi, may reduce the incidence and severity of R. equi pneumonia on farms.  相似文献   

20.
One hundred strains of Corynebacterium equi were examined using standard laboratory procedures. Variations in colonial morphology were noted. The ability to reduce nitrate and to produce urease was shown to be valuable for confirmation of identification of C. equi. Production of hydrogen sulphide was a variable characteristic of C. equi. It is concluded that for those situations where the source of the organism gives no clue as to its identify, positive identification of C. equi may be difficult because of variability in colonial appearance and biochemical reactions.  相似文献   

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