EQUINE HERPESVIRUS TYPE-2 (EHV-2) AS A PREDISPOSING FACTOR FOR RHODOCOCCUS-EQUI PNEUMONIA IN FOALS - PREVENTION OF THE BIFACTORIAL DISEASE WITH EHV-2 IMMUNOSTIMULATING COMPLEXES

Equine herpesvirus type 2 (EHV-2), a member of the Gammaherpesvirinae subfamily, was studied in a two-phase respiratory disease complex of y oung foals as a predisposing factor for the secondary bacterial invasi on of lungs with Rhodococcus equi (R. equi). Foals were immunized agai nst EHV-2 on a farm where R. equi pneumonia regularly occurred during the last years. The immunizations were performed by using a subunit va ccine which selectively presents envelope glycoproteins of EHV-2 in a multimeric form of immunostimulating complexes (iscoms). The etiologic al role of EHV-2 was estimated by observing the occurrence of the resp iratory disease complex in groups of foals immunized against the virus , in comparison to non-immunized controls, The immunization trials of young animals revealed that the iscom subunit vaccine formulation is a ble to overcome the interference of maternal antibodies. Active immuni zation of foals with a single dose of the iscoms provided a certain de gree of protection, while two injections of iscoms yielded complete pr otection against the disease complex in the majority of the treated an imals, by preventing the manifestation of R. equi pneumonia. The prese nt findings strongly support the hypothesis that EHV-2 is a predisposi ng factor for the R. equi invasion of the respiratory tract. The EHV-2 iscom formulation provides highly specific and effective means to pre vent the disease complex.