Fecal concentration of Rhodococcus equi determined by quantitative polymerase chain reaction of rectal swab samples to differentiate foals with pneumonia from healthy foals.
Abstract: Diagnostic accuracy of real-time, quantitative PCR (qPCR) assays to quantify virulent Rhodococcus equi using rectal swab samples has not been systematically evaluated. Objective: To evaluate the accuracy of qPCR of rectal swab samples to differentiate foals with pneumonia from healthy foals of similar age from the same environment. Methods: One hundred privately owned foals born in 2021 from 2 farms in New York. Methods: An incident case-control study design was used. Rectal swabs were collected from all foals diagnosed with R. equi pneumonia at 2 horse-breeding farms (n = 47). Eligible pneumonia cases (n = 39) were matched by age to up to 2 healthy (n = 53) control foals; rectal swabs were collected from control foals on the day of diagnosis of the index case. DNA was extracted from fecal swabs and the concentration of virulent R. equi (ie, copy numbers of the virulence-associated protein A gene [vapA] per 100 ng fecal DNA) was estimated by qPCR. Results: The area under the ROC curve for qPCR of fecal swabs was 83.7% (95% CI, 74.9-92.6). At a threshold of 14 883 copies of vapA per 100 ng fecal DNA, specificity of the assay was 83.0% (95% CI, 71.7-92.4) and sensitivity was 79.5% (95% CI, 66.7-92.3). Conclusions: Although fecal concentrations of virulent R. equi are significantly higher in pneumonic foals than healthy foals of similar age in the same environment, qPCR of rectal swabs as reported here lacks adequate diagnostic accuracy for clinical use.
© 2022 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals LLC on behalf of American College of Veterinary Internal Medicine.
Publication Date: 2022-04-27 PubMed ID: 35475581PubMed Central: PMC9151472DOI: 10.1111/jvim.16438Google Scholar: Lookup
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Summary
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This research aimed to assess the diagnostic accuracy of quantitative PCR (qPCR) assays, which quantify virulent Rhodococcus equi (a bacterium that causes pneumonia in foals) using rectal swab samples. The study found that although foals with pneumonia had significantly higher fecal concentrations of R. equi than healthy foals, the use of rectal swabs in qPCR, as currently practiced, lacks sufficient diagnostic accuracy for clinical use.
Objective
The research focused on evaluating the accuracy of qPCR assays that analyse rectal swab samples to distinguish between foals with pneumonia and healthy ones living within the same environment and of the same age bracket.
Methods
- The researchers conducted an incident case-control study with 100 foals born in the year 2021 across 2 horse-breeding farms in New York. These foals became the subjects of the study.
- Rectal swabs were collected from all foals diagnosed with R. equi pneumonia, totalling to a number of 47.
- Out of the 47 confirmed pneumonia cases, 39 were used as eligible pneumonia cases. These were matched, by age, with 53 healthy control foals. The rectal swabs were collected from these control foals on the day the index case was diagnosed.
- From these collected fecal swabs, DNA was extracted and the concentration of virulent R. equi (expressed in copy numbers of the virulence-associated protein A gene [vapA] per 100 ng fecal DNA) was estimated through qPCR.
Results
- The outcomes revealed an area under the ROC curve for qPCR of fecal swabs of 83.7% (95% CI, 74.9-92.6).
- At a threshold of 14 883 copies of vapA per 100 ng fecal DNA, the assay provided a specificity of 83.0% (95% CI, 71.7-92.4) and a sensitivity of 79.5% (95% CI, 66.7-92.3).
Conclusions
The results reached the conclusion that despite foals suffering from pneumonia recording significantly elevated fecal concentrations of virulent R. equi than healthy foals within a similar age bracket and environment, the practice of qPCR from rectal swab samples currently lacks sufficient diagnostic accuracy for clinical application. The authors therefore suggest continued exploration for more precise diagnostic methods.
Cite This Article
APA
Cohen ND, Flores-Ahlschewde P, Gonzales GM, Kahn SK, da Silveira BP, Bray JM, King EE, Blair CC, Bordin AI.
(2022).
Fecal concentration of Rhodococcus equi determined by quantitative polymerase chain reaction of rectal swab samples to differentiate foals with pneumonia from healthy foals.
J Vet Intern Med, 36(3), 1146-1151.
https://doi.org/10.1111/jvim.16438 Publication
Researcher Affiliations
- Equine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
- Rood & Riddle Equine Hospital in Saratoga, Saratoga Springs, New York, USA.
- Equine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
- Equine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
- Equine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
- Equine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
- Rood & Riddle Equine Hospital in Saratoga, Saratoga Springs, New York, USA.
- Equine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
- Equine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
MeSH Terms
- Actinomycetales Infections / diagnosis
- Actinomycetales Infections / veterinary
- Animals
- Case-Control Studies
- Horse Diseases / diagnosis
- Horses / genetics
- Pneumonia / veterinary
- Real-Time Polymerase Chain Reaction / veterinary
- Rhodococcus equi
Grant Funding
- Boehringer-Ingelheim Animal Health (Advancement in Equine Research Award)
- Link Equine Research Endowment, Texas A&M University, Equine Infectious Disease Epidemiology Program
Conflict of Interest Statement
Authors declare no conflict of interest.
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