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  • Author or Editor: Ronald J. Martens x
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Abstract

Objective—To identify farm characteristics as risk factors for the 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, 1 for a farm with ≥ 1 foal with R equi pneumonia and 1 for an unaffected control farm. Matched data were compared by use of conditional logistic regression analysis.

Results—Farm characteristics found in bivariate analyses to be associated with increased risk for pneumonia caused by R equi in foals included > 200 farm acres, ≥ 60 acres used in the husbandry of horses, > 160 horses, ≥ 10 mares housed permanently on the farm (resident mares), > 17 foals, > 0.25 foals/acre, and the presence of transient mares (mares brought temporarily to the farm for breeding or foaling) and their foals. Affected farms were significantly more likely to be > 200 acres in size and have ≥ 10 resident dam-foal pairs, whereas control farms were significantly more likely to have ≥ 75% of their dam-foal pairs housed permanently on the farm.

Conclusions and Clinical Relevance—Breeding farms with large acreage, a large number of mares and foals, high foal density, and a population of transient mares and foals are at high risk for foals developing pneumonia caused by R equi. (J Am Vet Med Assoc 2003;222:467–475)

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in Journal of the American Veterinary Medical Association

Abstract

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.

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in Journal of the American Veterinary Medical Association

Abstract

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 ≥ 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 RelevanceRhodococcus 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. (J Am Vet Med Assoc 2003; 222:476–485)

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in Journal of the American Veterinary Medical Association

Abstract

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 equiisolate. 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. (Am J Vet Res 2005;66:1380–1385)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To quantify and compare geochemical factors in surface soils from horse-breeding farms with horses with pneumonia caused by Rhodococcus equi (affected farms) and horse-breeding farms with no history of pneumonia caused by R equi (unaffected farms).

Sample Population—Soil from 24 R equi-affected farms and 21 unaffected farms.

Procedure—Equine veterinary practitioners throughout Texas submitted surface soil samples from areas most frequented by foals, on R equi affected and unaffected horse-breeding farms in their practice. Soil samples were assayed for the following factors: pH, salinity, nitrate, phosphorus, potassium, calcium, magnesium, sodium, sulfur, zinc, iron, manganese, and copper. Median values for all factors were recorded, and differences between affected and unaffected farms were compared.

Results—Significant differences in soil factors were not detected between affected and unaffected farms; hence, there was no association between those factors and R equi disease status of the farms.

Conclusion and Clinical Relevance—The surface soil factors monitored in this study were not significant risk factors for pneumonia caused by R equi. As such, it is not possible to determine whether foals on a given farm are at increased risk of developing disease caused by R equi on the basis of these factors. Data do not support altering surface soil for factors examined, such as alkalinization by applying lime, as viable control strategies for R equi. (Am J Vet Res 2002;63:95–98)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To characterize changes in lymphocyte subsets over time in foals from birth to 18 weeks of age, accounting for differences among individuals, and to determine the effect of overnight storage of blood samples on foal lymphocyte subset concentrations.

Animals—8 healthy Quarter Horse foals from birth to 18 weeks of age.

Procedure—Blood samples were collected longitudinally from birth to 18 weeks of age and a CBC performed on each sample. The samples were stained for lymphocyte markers, either immediately or after overnight storage and analyzed by flow cytometry.

Results—Total leukocytes, total lymphocytes, and the absolute concentrations of all lymphocyte subsets increased significantly with age. The proportions of B29A+, CD21+, and equine major histocompatability complex class-II molecule+ lymphocytes increased significantly with age. The proportion of equine (Eq) CD5+, EqCD8+, and EqWC4+ lymphocytes decreased significantly with age. Significant differences among foals were found with respect to initial concentrations with respect to initial concentrations, but not with respect to the rate of increase of the various subsets tested. Significant differences were not found in subset values when comparing blood samples stained on the day of collection or after overnight storage at room temperature (approx 21 C) or under refrigeration.

Conclusions and Clinical Relevance—These results are consistent with an increase in subset numbers and proportions over time, but with individual differences among foals. The observation of individual differences in subsets among foals suggests that there may be individual differences in susceptibility to infectious disease during the perinatal period. The absence of an effect of overnight storage makes field studies of lymphocyte subset concentrations more feasible. (Am J Vet Res 2002;63:531–537)

Full access
in American Journal of Veterinary Research

Abstract

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. (J Am Vet Med Assoc 2003;223:1791–1799)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To identify farm characteristics and management practices associated with development of Rhodococcus equi pneumonia in foals.

Design—Prospective case-control study.

Animals—5,230 foals on 138 breeding farms with 9,136 horses.

Procedure—During 2003, participating veterinarians provided data from 1 or 2 farms with ≥ 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 ≥ 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. (J Am Vet Med Assoc 2005;226:404–413)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To evaluate a real-time quantitative polymerase chain reaction (QPCR) assay in the detection and quantitation of virulent Rhodococcus equi.

Sample Population—1 virulent, 2 intermediately virulent, and 2 avirulent strains of R equi and 16 isolates of bacteria genetically related to R equi.

Procedure—The QPCR assay was evaluated for detection and quantitation of the virulence-associated gene (vapA) of R equi in pure culture and in samples of tracheobronchial fluid, which were inoculated with known numbers of virulent R equi. Results were compared with those derived via quantitative microbial culture and standard polymerase chain reaction methods.

Results—The QPCR assay detected the vapAgene in pure culture of R equi and in tracheobronchial fluid samples that contained as few as 20 CFUs of virulent R equi/mL and accurately quantitated virulent R equi to 103 CFUs/mL of fluid. The assay was highly specific for detection of the vapA gene of virulent R equi and was more sensitive than standard polymerase chain reaction for detection of R equi in tracheobronchial fluid.

Conclusions and Clinical Relevance—The QPCR assay appears to be a rapid and reliable method for detecting and quantitating virulent R equi. The accuracy of the QPCR assay is comparable to that of quantitative microbial culture. The increased sensitivity of the QPCR method in detection of virulent R equi should facilitate rapid and accurate diagnosis of R equi pneumonia in foals. (Am J Vet Res 2005;66:755–761)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the chemoprophylactic effect of gallium maltolate on the cumulative incidence of pneumonia caused by Rhodococcus equi infection in foals.

Animals—483 foals born and raised on 12 equine breeding farms with a history of endemic R equi infections.

Procedures—Group 1 foals were treated with a placebo and group 2 foals were treated with gallium maltolate (approx 30 mg/kg, PO, q 24 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 gallium maltolate.

Results—There were no significant differences in the cumulative incidence of R equi pneumonia among the 2 groups.

Conclusions and Clinical Relevance—Chemoprophylaxis via gallium maltolate administered orally at approximately 30 mg/kg daily for the first 2 weeks after birth failed to reduce the cumulative incidence of pneumonia attributable to R equi infection among foals on breeding farms with endemic R equi infections. Further investigation is needed to identify strategies for control of R equi infections.

Full access
in American Journal of Veterinary Research