Immunocytochemical detection of Rhodococcus equi in tracheal washes of foals

The aim of the present study was to develop an immunocytochemical procedure for the early detection and demonstration of Rhodococcus equi in smears of tracheal aspirates taken from live foals in field conditions. Tracheal wash samples were collected from thoroughbred foals, aged 1-5 months and located in studs around Bursa and Istanbul, Turkey. Some foals were suspected of having R. equi infection on the basis of clinical examination (n=56) and others were unaffected control animals (n=54). Serum samples were also collected from each foal for testing for the presence of R. equi-specific antibody by enzyme linked immunosorbent assay (ELISA). Thirty-six of the control foals (66.7%) and 37 of the affected foals (66.1%) were seropositive for R. equi. Immunocytochemical labelling was detected in the smears from 73.2% of the affected foals and 70.4% of the control foals. For both ELISA and immunocytochemistry (ICC), there was no significant difference between the affected and control foals (P>0.05) and there was no significant difference between the two test modalities (P>0.05). ICC may therefore have similar diagnostic utility when compared with ELISA. There is no clear relationship between clinical signs and ELISA or ICC positivity.