Infection of specific-pathogen-free lambs with parainfluenza virus type 3, Pasteurella haemolytica and Mycoplasma ovipneumoniae

Abstract

Groups of specific-pathogen-free lambs were inoculated with combinations of parainfluenza virus type 3 (PI 3), Pasteurella haemolytica (P.h.) and Mycoplasma ovipneumoniae ( (M.o.). Acute, necrotising bronchopneumonia developed in 8/9 lambs inoculated with PI 3 followed by P.h. whereas only 1/5 lambs inoculated with PI 3 followed by a combination of M.o. and P.h. developed a pneumonic lesion. When M.o. was inoculated 29 days before PI 3 and P.h., pneumonia developed in 3/4 lambs but M.o. was not reisolated from any of the lungs. Pneumonia was observed in 1/5 lambs inoculated with P.h. alone and in 1/5 inoculated with M.o. plus P.h. In addition, one lamb in the latter group died of acute septicaemic pasteurellosis. None of the lambs inoculated with M.o. alone, PI 3 alone or PI 3 followed by M.o. had any gross or microscopic evidence of pneumonia although the virus alone, or in combination, did produce minor pulmonary lesions. These data suggest that M.o. is not an important primary or secondary lung pathogen.