Isolation of Virulent Rhodococcus equi from Transtracheal Aspirates of Foals Serodiagnosed by Enzyme-Linked Immunosorbent Assay.

Abstract

ABSTRACT. Although isolation of Rhodococcus equi from tracheobronchial aspirates is thought to be a definitive diagnosis of R. equi pneumonia in foals, virulence of isolates from the aspirates of infected foals remains obscure. In the present study, transtracheal aspirates were collected from thirty-one 1-to 6-month-old foals, which showed clinical signs of respiratory tract infection, and R. equi isolates were analyzed for the presence of virulence plasmids and virulence-associated antigens. Moreover, this method was compared with a serodiagnosis by an enzyme-linked immunosorbent assay (ELISA) to evaluate the sensitivity of the ELISA. Of the 31 foals, 21 revealed positive cultures for R. equi. Of the 21 foals, 20 (95%) had an ELISA OD value of 0.3 (positive limit of this test) or higher at the initial medical examination. All of the isolates from the aspirates were virulent R. equi, which contained virulence plasmids and expressed virulence-associated antigens. In the remaining 10 foals showing a negative culture for R. equi, 3 foals had positive ELISA titers. Six foals died during the treatment, and necropsy revealed that 5 of the 6 foals had R. equi infection characterized by large abscesses in the lungs, and 3 of the 5 foals also had intestinal lesions. All clinical isolates from the lesions of the foals were virulent R. equi. These results support the assumption that isolates from the transtracheal aspirates of infected foals are virulent R. equi and the sensitivity of ELISA might demonstrate a serodiagnostic value for early diagnosis of R. equi infection in foals. -KEY WORDS: foal, Rhodococcus equi, tracheal aspirate, virulence.

Chemoprophylactic effects of azithromycin against Rhodococcus equi–induced pneumonia among foals at equine breeding farms with endemic infections

“…Sensitivity ranges from 57% to 100%. [46][47][48][49][50][51][52][53] We have used similar diagnostic criteria for classification of affected and unaffected foals in other studies 9,24-27 of pneumonia attributable to R equi, and we believe that misclassification is infrequent.…”

B-Cell Epitope Mapping of the VapA Protein of Rhodococcus equi : Implications for Early Detection of R. equi Disease in Foals

“…This protein is 15 to 17 kDa and is encoded by a gene present on a large 85-to 90-kb plasmid. Previous studies have shown that the majority of clinical R. equi isolates from foals, unlike environmental isolates, typically contain this virulence plasmid (8,20). Giguere et al have shown that this plasmid plays a role in the intracellular survival and replication of R. equi in host macrophages and consequently is an important factor for the development of R. equi disease in foals (5).…”

Performance of Five Serological Assays for Diagnosis ofRhodococcus equiPneumonia in Foals

“…In another study with ELISA-6939, 20 (95%) of 21 foals with culture-confirmed R. equi pneumonia had an optical density value of 0.3 or greater, indicating good sensitivity of the assay (12). However, the diagnostic performance of the assay (sensitivity, specificity, and predictive values) on a farm where R. equi infections are enzootic was not determined.…”