ULTRASTRUCTURAL-STUDY OF PORCINE ALVEOLAR MACROPHAGES INFECTED IN-VITRO WITH PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME (PRRS) VIRUS, WITH AND WITHOUT HAEMOPHILUS-PARASUIS

Two experiments were designed to study ultrastructural changes in porc ine alveolar macrophages (PAM) inoculated with porcine reproductive an d respiratory syndrome (PRRS) virus (experiment 1) and with PRRS virus and Haemophilus parasuis (experiment 2). In both experiments, the vir al infectious dose represented a ''multiplicity of infection'' of 1. V iral infection alone induced minimal ultrastructural changes at this d ose, consisting only of an increase in lysosome numbers. Mixed viral a nd bacterial infection induced the production of greatly increased num bers of phagosomes and phagolysosomes. The PAM were of low efficacy in phagocytizing H. parasuis. PRRS virus infection had only a minimal ef fect on the phagocytosis of H. parasuis by PAM. It is suggested that t he virus induces PAM activation rather than PAM destruction. (C) 1998 W.B. Saunders Company Limited.