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

Groups of specific-pathogen-free lambs were inoculated with combinations of para-influenza virus type 3 (PI sub(3)), Pasteurella haemolytica) (P.h.) and Mycoplasma ovipneumoniae (M.o. ). Acute, necrotising bronchopneumonia developed in 8/9 lambs inoculated with PI sub(3) followed by P.h.), whereas only 1/5 lambs inoculated with PI sub(3) followed by a combination of M.o.) and P.h. developed a penumonic lesion. When M.o. was inoculated 29 days before PI sub(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 sub(3) alone or PI sub(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.