Porcine reproductive and respiratory syndrome virus (PRRSV): Kinetics of infection in lymphatic organs and lung

Pigs were infected by the oronasal route with European isolates of the porc ine reproductive and respiratory syndrome virus (PRRSV; I10 and Cobbelsdorf ). The kinetics of infection in lymphatic organs and the lung were analysed by immunofluorescence detection of virus antigen, re-isolation of the viru s and reverse transcription-polymerase chain reaction (RT-PCR) for PRRSV-sp ecific RNA. The kinetics of PRRSV infection proceeded in three phases, irre spective of thr varying infestation of lymphatic organs within the first da ys post-infection (p.i.). First, an early acute infection of lymphatic orga ns developed within the first week and was characterized by a high number o f antigen-positive macrophages. Second, a delayed acute infection of the lu ng was observed, which was most pronounced during the second and third week p.i. when a high number of infected alveolar macrophages was observed. The acute infection of lymphatic organs had resolved at this time. Infected ce lls in the lung were predominantly located in pneumonic lesions. Third, a p ersistent infection was demonstrated by RT-PCR and immunohistology when the experiments were terminated at day 43 p.i. The virus persisted in lymphati c organs, especially In the tonsils, and in the lung. At this stage, indica tions for a re-occurrence of acute infection mere observed in restricted ar eas of the lung.