COMPARISON OF TRACHEAL ASPIRATION WITH OTHER TESTS FOR DIAGNOSIS OF RHODOCOCCUS-EQUI PNEUMONIA IN FOALS

The diagnostic value of tracheal aspiration was evaluated through comp arison with other diagnostic methods using an experimental model of Rh odococcus equi (R. equi) pneumonia in foals. Pneumonia was induced by spraying of the virulent R. equi strain ATCC 33701 into the trachea of foals. All foals developed fever from 11 to 16 days after bacterial i noculation. One foal was euthanized on day 26 due to its poor prognosi s, and other foals euthanized on day 43. During the experiment, some t ests for diagnosis of Rhodococcus equi pneumonia such as tracheal aspi ration, radiography, serodiagnosis and fecal culture were carried out, R. equi was continually isolated from tracheal aspirates collected vi a a silicone catheter inserted transnasally on day 8 to day 32 after b acterial inoculation. On the other hand, radiography, serodiagnosis an d fecal culture were demonstrated to be valuable diagnostic methods, b ut to be limited compared with tracheal aspiration. Indirect fluoresce nt antibody technique (IFA) using a monoclonal antibody against the 15 - to 17-kDa virulence-associated antigens (VapA) of R. equi and PCR ta rgeting the structural gene of VapA detected bacteria in tracheal aspi rates less sensitively than the isolation technique although they were more rapid. Therefore, we conclude that a combination of tracheal asp iration and bacterial isolation was the most valuable method for routi ne diagnosis of R. equi pneumonia in foals. (C) 1997 Elsevier Science B.V.