Objective—To determine whether the concentrations of airborne virulent Rhodococcus equi in stalls housing foals during the first 2 weeks after birth are associated with subsequent development of R equi pneumonia in those foals.
Sample—Air samples collected from foaling stalls and holding pens in which foals were housed during the first 2 weeks after birth.
Procedures—At a breeding farm in Texas, air samples (500 L each) were collected (January through May 2011) from stalls and pens in which 121 foals were housed on day 1 and on days 4, 7, and 14 after birth. For each sample, the concentration of airborne virulent R equi was determined with an immunoblot technique. The association between development of pneumonia and airborne R equi concentration was evaluated via random-effects Poisson regression analysis.
Results—Some air samples were not available for analysis. Of the 471 air samples collected from stalls that housed 121 foals, 90 (19%) contained virulent R equi. Twenty-four of 121 (20%) foals developed R equi pneumonia. Concentrations of virulent R equi in air samples from stalls housing foals that developed R equi pneumonia were significantly higher than those in samples from stalls housing foals that did not develop pneumonia. Accounting for disease effects, air sample concentrations of virulent R equi did not differ significantly by day after birth or by month of birth.
Conclusions and Clinical Relevance—Exposure of foals to airborne virulent R equi during the first 2 weeks after birth was significantly (and likely causally) associated with development of R equi pneumonia.
Objective—To develop a method for typing
Streptococcus equi on the basis of the DNA
sequence of the genes that produce an M-like protein
and to compare isolates among the United States,
Japan, and other countries.
Sample Population—S equi strains CF32, Hidaka/95/2,
and NCTC9682 as well as 82 other isolates from the
United States, Japan, and other countries obtained during
1975 to 2001.
Procedure—DNA sequences of the structural genes
( SeM and SzPSe) that produce M-like proteins were
determined for 3 representative strains to find a variable
region. Variability in this region of SeM was then
determined for the other isolates. Amino acid
sequences were deduced and analyzed phylogenetically
by use of the neighbor-joining method.
Results—Sequence diversity was detected in the
N-terminal region of SeM but not in SzPSe of the 3
representative strains. Base substitutions in the
variable region of SeM varied in a nonsynonymous
manner, resulting in variation in the amino acid
sequence. Eighty-five isolates were categorized as
32 types of SeM on the basis of differences in the
deduced amino acid sequences.
Conclusions and Clinical Relevance—This study
documented a region in the N-terminal portion of
SeM that varies in a nonsynonymous manner. This
information should be useful in molecular epidemiologic
studies of S equi. (Am J Vet Res 2005;
Objective—To determine whether mares are a clinically important source of Rhodococcus equi for their foals.
Sample Population—171 mares and 171 foals from a farm in Kentucky (evaluated during 2004 and 2005).
Procedures—At 4 time points (2 before and 2 after parturition), the total concentration of R equi and concentration of virulent R equi were determined in fecal specimens from mares by use of quantitative bacteriologic culture and a colony immunoblot technique, respectively. These concentrations for mares of foals that developed R equi–associated pneumonia and for mares with unaffected foals were compared. Data for each year were analyzed separately.
Results—R equi–associated pneumonia developed in 53 of 171 (31%) foals. Fecal shedding of virulent R equi was detected in at least 1 time point for every mare; bacteriologic culture results were positive for 62 of 171 (36%) mares at all time points. However, compared with dams of unaffected foals, fecal concentrations of total or virulent R equi in dams of foals with R equi–associated pneumonia were not significantly different.
Conclusions and Clinical Relevance—Results indicate that dams of foals with R equi–associated pneumonia did not shed more R equi in feces than dams of unaffected foals; therefore, R equi infection in foals was not associated with comparatively greater fecal shedding by their dams. However, detection of virulent R equi in the feces of all mares during at least 1 time point suggests that mares can be an important source of R equi for the surrounding environment.
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.
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 agematched
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. (J Am Vet Med Assoc 2002;221:825–833)
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 (VapAP)
and resistance to the β-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 β-lactam
antibiotics. No association between β-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. (J Am Vet Med Assoc 2000;217:220–225)
Objective—To compare isolates of Rhodococcus
equi on the basis of geographic source and virulence
status by use of pulsed-field gel electrophoresis
Sample Population—290 isolates of R equi(218 virulent
isolates from foals and 72 avirulent isolates from
feces, soil, and respiratory tract samples) obtained
between 1985 and 2000 from horses and horse farms
from 4 countries.
Procedure—DNA from isolates was digested with
the restriction enzyme AseI and tested by use of
PFGE. Products were analyzed for similarities in banding
patterns by use of dendrograms. A similarity
matrix was constructed for isolates, and the matrix
was tested for nonrandom distributions of similarity
values with respect to groupings of interest.
Results—There was little grouping of isolates on the
basis of country, virulence status, or region within
Texas. Isolates of R equi were generally < 80% similar,
as determined by use of PFGE. Isolates from the
same farm generally were rarely of the same strain.
Conclusions and Clinical Relevance—Considerable
chromosomal variability exists among isolates of R
equi obtained from the same farm, sites within Texas,
or among countries from various continents. Only
rarely will it be possible to link infections to a given
site or region on the basis of analysis of isolates by
use of PFGE of chromosomal DNA. (Am J Vet Res 2003;64:153–161)
Objective—To determine whether airborne concentrations of virulent Rhodococcus equi at 2 horse breeding farms varied on the basis of location, time of day, and month.
Sample Population—2 farms in central Kentucky with recurrent R equi-induced pneumonia in foals.
Procedures—From February through July 2008, air samples were collected hourly for a 24-hour period each month from stalls and paddocks used to house mares and their foals. Concentrations of airborne virulent R equi were determined via a modified colony immunoblot technique. Differences were compared by use of zero-inflated negative binomial methods to determine effects of location, time, and month.
Results—Whether mares and foals were housed predominantly in stalls or paddocks significantly affected results for location of sample collection (stall vs paddock) by increasing airborne concentrations of virulent R equi at the site where horses were predominantly housed. Airborne concentrations of virulent R equi were significantly higher from 6:00 pm through 11:59 pm than for the period from midnight through 5:59 am. Airborne concentrations of virulent R equi did not differ significantly between farms or among months.
Conclusions and Clinical Relevance—Airborne concentrations of virulent R equi were significantly increased when horses were predominantly housed at the site for collection of air samples (ie, higher in stalls when horses were predominantly housed in stalls and higher in paddocks when horses were predominantly housed in paddocks). Concentrations of virulent R equi among air samples collected between the hours of 6:00 am and midnight appeared similar.
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.
Objective—To determine whether the concentration of airborne virulent Rhodococcus equi varied by location (stall vs paddock) and month on horse farms.
Sample—Air samples from stalls and paddocks used to house mares and foals on 30 horse breeding farms in central Kentucky.
Procedures—Air samples from 1 stall and 1 paddock were obtained monthly from each farm from January through June 2009. Concentrations of airborne virulent R equi were determined via a modified colony immunoblot assay. Random-effects logistic regression was used to determine the association of the presence of airborne virulent R equi with location from which air samples were obtained and month during which samples were collected.
Results—Of 180 air samples, virulent R equi was identified in 49 (27%) and 13 (7%) obtained from stalls and paddocks, respectively. The OR of detecting virulent R equi in air samples from stalls versus paddocks was 5.2 (95% confidence interval, 2.1 to 13.1). Of 60 air samples, virulent R equi was identified in 25 (42%), 18 (30%), and 6 (10%) obtained from stalls during January and February, March and April, and May and June, respectively. The OR of detecting virulent R equi from stall air samples collected during May and June versus January and February was 0.22 (95% confidence interval, 0.08 to 0.63).
Conclusions and Clinical Relevance—Foals were more likely to be exposed to airborne virulent R equi when housed in stalls versus paddocks and earlier (January and February) versus later (May and June) during the foaling season.