Porcine Reproductive and Respiratory Syndrome Virus (PRRSV): Kinetics of Infection in Lymphatic Organs and Lung

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Abstract
Summary: Pigs were infected by the oronasal route with European isolates of the porcine 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 virus and reverse transcription‐polymerase chain reaction (RT‐PCR) for PRRSV‐specific RNA. The kinetics of PRRSV infection proceeded in three phases, irrespective of the varying infestation of lymphatic organs within the first days post‐infection (p.i.). First, an early acute infection of lymphatic organs developed within the first week and was characterized by a high number of antigen‐positive macrophages. Second, a delayed acute infection of the lung 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 cells in the lung were predominantly located in pneumonic lesions. Third, a persistent infection was demonstrated by RT‐PCR and immunohistology when the experiments were terminated at day 49 p.i. The virus persisted in lymphatic organs, especially in the tonsils, and in the lung. At this stage, indications for a re‐occurrence of acute infection were observed in restricted areas of the lung.

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