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 determine factors associated with
development of postoperative ileus (POI) in horses
undergoing surgery for colic.
Design—Prospective case-control study.
Animals—251 horses undergoing colic surgery, of
which 47 developed POI.
Procedure—Signalment, history, clinicopathologic
data, pre- and postoperative treatments, lesions,
complications, costs, and outcome were recorded for
all horses during hospitalization.
Results—Variables associated with increased odds of
POI included small intestinal lesion, high PCV, and
increased duration of anesthesia. There was modest
evidence that pelvic flexure enterotomy and intraoperative
administration of lidocaine may have reduced
the odds of developing POI.
Conclusions and Clinical Relevance—Findings during
the preoperative and intraoperative periods can be used
to identify horses at increased risk of POI. Reducing surgical
and anesthetic duration should decrease the incidence
of POI. ( J Am Vet Med Assoc 2004;225:
To compare soil concentrations of macrolide- and rifampicin-resistant Rhodococcus equi strains (MRRE) on horse-breeding farms that used thoracic ultrasonographic screening (TUS) to identify foals with subclinical pneumonia combined with subsequent administration of macrolides and rifampin to affected foals (TUS farms) versus soil concentrations on farms that did not (non-TUS farms), determine whether the combined use of TUS and antimicrobial treatment of subclinically affected foals was associated with soil concentration of MRRE, and assess whether there were temporal effects on soil concentrations of MRRE during the foaling season.
720 soil samples and 20 completed questionnaires from 20 horse-breeding farms (10 TUS farms and 10 non-TUS farms) in central Kentucky.
A questionnaire was used to gather information from participating farms about their 2019 foaling season. Soil samples were collected during January, March, May, and July 2019 for bacterial culture and antimicrobial susceptibility testing to identify any isolates of MRRE. Results were compared for TUS farms versus non-TUS farms. Linear mixed-effects modeling was used to evaluate for potential associations between the soil concentration of MRRE and the use of TUS.
Overall, the sum of the mean soil concentrations of MRRE was significantly higher for TUS farms (8.85 log10-transformed CFUs/g) versus non-TUS farms (7.37 log10-transformed CFUs/g).
CONCLUSIONS AND CLINICAL RELEVANCE
Our findings indicated that farms that use TUS to identify foals with subclinical pneumonia for antimicrobial treatment select for antimicrobial-resistant R equi strains. Because prognosis is worse for foals infected with resistant versus nonresistant strains of R equi, prudent use of antimicrobials to treat foals with subclinical pulmonary lesions attributed to R equi is recommended.
Objective—To determine whether administration of
killed West Nile virus vaccine was associated with
pregnancy loss among broodmares.
Design—Retrospective cohort study.
Procedure—Records of pregnant mares with known
vaccination history from 4 farms were reviewed.
Information obtained from 595 mares included mare's
identification; farm; age; breed; reproductive status;
last breeding date; date last known pregnant; vaccination
date; age of conceptus at vaccination; vaccination
during the early embryonic, early fetal, and late fetal
periods; and whether an early embryonic death (EED),
early fetal loss (EFL), or late fetal loss (LFL) occurred.
The relationships between the dichotomous outcomes
of loss (eg, EED, EFL, LFL) and independent categoric
variables (eg, vaccination during the early embryonic,
early fetal, or late fetal periods) were examined.
Results—Vaccination of pregnant mares during any
period of gestation was not associated with increased
incidence of pregnancy loss.
Conclusions and Clinical Relevance—Many mares
are already pregnant at the onset of mosquito season,
when mares are more likely to be vaccinated than at
other times. Our findings provide evidence that vaccine
administration will not compromise pregnancy in
horses. (J Am Vet Med Assoc 2004;225:1894–1897)
Objective—To identify factors significantly associated
with an epidemic of fibrinous pericarditis during
spring 2001 among horses in central Kentucky.
Animals—38 horses with fibrinous pericarditis and
30 control horses examined for other reasons.
Procedure—A questionnaire was developed to solicit
information regarding a wide range of management
practices and environmental exposures from farm
owners or managers.
Results—The following factors were found in bivariate
analyses to be significantly associated with an
increased risk of pericarditis: being from a farm with
mares and foals affected by mare reproductive loss
syndrome, exposure to Eastern tent caterpillars in or
around horse pastures, younger age, shorter duration
of residence in Kentucky and at the farm of current
residence, being fed hay grown outside Kentucky, a
lack of access to pond water, access to orchard grass
for grazing, and a lack of direct contact with cattle. In
multivariate logistic regression analyses, only variables
related to caterpillar exposure and age were significantly
associated with fibrinous pericarditis.
Conclusions and Clinical Relevance—Results suggest
that fibrinous pericarditis in horses may be associated
with mare reproductive loss syndrome. Exposure
to Eastern tent caterpillars was the greatest risk factor
for development of fibrinous pericarditis. The distribution
of times of diagnosis of fibrinous pericarditis was
consistent with a point-source epidemic. (J Am Vet Med
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.
Objective—To identify factors associated with abortions
during early gestation classified as mare reproductive
loss syndrome (MRLS).
Animals—324 broodmares from 43 farms in central
Kentucky, including 121 mares from 25 farms that
had early-term abortions (ETAs) associated with
MRLS (case horses), 120 mares from the same farms
but that did not abort, and 83 mares from 18 farms
that were not severely impacted by MRLS.
Procedure—Farm managers were interviewed to
obtain data on various management practices and
environmental exposures for the mares. Data for case
and control horses were compared to identify risk factors
for mares having MRLS-associated ETAs.
Results—Several factors increased the risk of MRLS-associated
ETAs, including feeding hay in pasture,
greater than usual amounts of white clover in pastures,
more eastern tent caterpillars in pastures, abortion
during a previous pregnancy, and sighting deer or
elk on the premises.
Conclusions and Clinical Relevance—Analysis indicates
that certain characteristics of pastures predisposed
mares to MRLS-associated ETAs. Methods for
limiting exposure to pasture (keeping mares in stalls
longer) during environmental conditions similar to
those of 2001 (ie, sudden freezing in mid-April following
warmer-than-usual springtime temperatures and
larger-than-usual numbers of eastern tent caterpillars
in and around pastures) should reduce the risk of
mares having MRLS-associated ETAs. It was not possible
to determine whether exposure to white clover
or caterpillars were causal factors for MRLS or were
merely indicators of unusual environmental conditions
that resulted in exposure of mares to a toxic or infectious
agent. (J Am Vet Med Assoc 2003;222:210–217)