B0026 - Ultrasensitive qualitative detection of
by real time polymerase chain reaction.
included in P0013 - equine
is a gram-positive, pleomorphic coccobacillus that is a frequent
cause of pneumonia and enteritis in foals, especially before 6
months of age. It has also been linked to a variety of
suppurative processes in immune-suppressed humans (Prescott,
1991). The organism has a worldwide distribution and can easily
be isolated from soil and environmental samples (Barton and
Hughes, 1984; Debey and Bailie, 1987; Takai et al., 1991).
Pathogenic R. equi
isolated from sick foals uniformly contain an 85- to 90-kb
plasmid known as vapA, which carries a gene responsible for
expression of a 15- to 17-kDa antigen of undetermined function (Takai
et al., 1991, 1993). Environmental strains of
R. equi not
associated with equine disease do not contain this plasmid.
The onset of
clinical signs of R. equi
pneumonia in foals is often subtle, and the infection is usually
not recognized until severe abscessation has occurred. By that
time, prognosis is poor. Culture of the organism from tracheal
wash was previously considered the "gold standard" for
diagnosis. However, it can be difficult to reliably culture
R. equi from a
tracheal wash sample, possibly because of prior antibiotic
administration or the presence of multiple pathogenic bacterial
species. A recent study has reported that only 62% of horses
with positive R. equi
cultures at necropsy, and 64% with radiographic evidence of
lung abscessation, yielded
R. equi on culture of tracheal wash (Hillidge,
1987), indicating an unacceptably high false negative rate using
detection of R. equi
can offer rapid detection of this pathogenic bacterium. A recent
study has shown that PCR of tracheal wash using primers that
recognized the vapA virulence plasmid of
R. equi has a
diagnostic sensitivity of 100% and specificity of 90.6%. In
contrast, sensitivity and specificity are only 57.1% and 93.8%,
respectively, for standard microbiologic culture of tracheal
wash and only 62.5% and 75.9%, respectively, for serology (Sellon
et al, 2001).
detection of R. equi
in tracheal wash fluid is more sensitive and specific for
diagnosis of R. equi
pneumonia than are other available diagnostic tests. This PCR
assay detects only pathogenic strains of
non-pathogenic environmental strains are not detected.
Help confirm the disease causing agent
Shorten the time required to confirm a clinical
diagnosis of R. equi
Help ensure that horse populations are free of
Early prevention of spread of this bacterium
Minimize personnel exposure to this bacterium
Safety monitoring of biological products that derive
Barton, M. D., and Hughes, K.L. (1984) Ecology of
Rhodococcus equi. Vet. Microbiol. 9:65-76.
Debey, M. C.,
and Bailie, W.E. (1987)
Rhodococcus equi in fecal and environmental samples
from Kansas horse farms. Vet. Microbiol. 14:251-257.
C. J. (1987) Use of erythromycin-rifampin combination in
treatment of Rhodococcus
equi pneumonia. Vet. Microbiol. 14:215-224.
Prescott, J. F. (1991)
Rhodococcus equi: an animal and human pathogen. Clin.
Microbiol. Rev. 4:20-34.
Sellon, D.C., Besser, T.E.,
Vivrette, S.L. and McConnico, R.S. (2001) Comparison of nucleic
acid amplification, serology, and microbiologic culture for
diagnosis of Rhodococcus
equi pneumonia in foals. J. Clin. Microbiol.
Takai, S., Ohbushi, S., Koike, K., Tsubaki, S.,
Oishi, H. and Kamada, M. (1991) Prevalence of virulent
Rhodococcus equi in
isolates from soil and feces of horses from horse-breeding farms
with and without endemic infections. J. Clin. Microbiol.
Takai, S., Sekizaki, T., Ozawa, T., Sugawara,
T., Watanabe, Y. and Tsubaki, S. (1991) Association between a
large plasmid and 15- to 17-kilodalton antigens in virulent
Infect. Immun. 59:4056-4060.
Takai, S., Watanabe, Y., Ikeda,
T., Ozawa, T., Matsukura, S., Tamada, Y., Tsubaki, S. and
Sekizaki, T. (1993) Virulence-associated plasmids in
Rhodococcus equi. J.
Clin. Microbiol. 31:1726-1729.
Nasopharyngeal swab, or 0.2 ml tracheal wash, or 0.2 ml whole
blood in EDTA (purple top) or ACD (yellow top) tube, or 0.2 ml
Contact Zoologix if advice is needed to determine an appropriate specimen type for a specific diagnostic application. For specimen types not listed here, please contact Zoologix to confirm specimen acceptability and shipping instructions.
specimen types, if there will be a delay in shipping, or during
very warm weather, refrigerate specimens until shipped and ship
with a cold pack unless more stringent shipping requirements are
specified. Frozen specimens should be shipped so as to remain
frozen in transit. See shipping
instructions for more information.
2 business days
Qualitative real time PCR