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Title: Mycoplasma ovipneumoniae can predispose bighorn sheep to fatal Mannheimia haemolytica pneumonia

item DASSANAYAKE, ROHANA - Washington State University
item SHANTHALINGAM, SUDARVILI - Washington State University
item HERNDON, CAROLINE - Washington State University
item SUBRAMANIAM, RENUKA - Washington State University
item LAWRENCE, PAULRAJ - Washington State University
item BAVANANTHASIVAM, JEGARUBEE - Washington State University
item CASSIRER, E - Washington State University
item HALDORSON, GARY - Washington State University
item FOREYT, WILLIAM - Washington State University
item RURANGIRWA, FRED - Washington State University
item Knowles Jr, Donald
item BESSER, THOMAS - Washington State University
item SRIKUMARAN, SUBRAMANIAM - Washington State University

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2010
Publication Date: 4/21/2010
Citation: Dassanayake, R.P., Shanthalingam, S., Herndon, C.N., Subramaniam, R., Lawrence, P.K., Bavananthasivam, J., Cassirer, E.F., Haldorson, G.J., Foreyt, W.J., Rurangirwa, F.R., Knowles Jr, D.P., Besser, T.E., Srikumaran, S. 2010. Mycoplasma ovipneumoniae can predispose bighorn sheep to fatal Mannheimia haemolytica pneumonia. Veterinary Microbiology. Available: doi:10.1016/j.vetmic.2010.04.011.

Interpretive Summary: Pneumonia of bighorn sheep is a population limiting disease. The organism Mycoplasma ovipneumoniae has been shown to be one of the pathogens associated with pneumonia in bighorn sheep. This report shows that while M. ovipneumoniae may not cause fatal pneumonia on its own, M. ovipneumoniae can predispose bighorn sheep to fatal pneumonia caused by the bacterium M.haemolytica. These data indicate that development of vaccines to prevent population limiting in bighorn sheep must consider both M. haemolytica and M. ovipneumoniae.

Technical Abstract: Mycoplasma ovipneumoniae has been isolated from the lungs of pneumonic bighorn sheep (BHS). However experimental reproduction of fatal pneumonia in BHS with M. ovipneumoniae was not successful. Therefore the specific role, if any, of M. ovipneumoniae in BHS pneumonia is unclear. The objective of this study was to determine whether M. ovipneumoniae alone causes fatal pneumonia in BHS, or predisposes them to infection by Mannheimia haemolytica. We chose M. haemolytica for this study because of its isolation from pneumonic BHS, and its ability to cause fatal pneumonia under experimental conditions. Since in vitro culture could attenuate virulence of M.ovipneumoniae, we used ceftiofur-treated lung homogenate from pneumonic BHS lambs or nasopharyngeal washing from M.ovipneumonia-positive domestic sheep (DS) as the source of M.ovipneumoniae. Two adult BHS were inoculated intranasally with lung homogenate while two others received nasopharyngeal washings from DS. All BHS developed clinical signs of pneumonia, but only one BHS died. The dead BHS had carried leukotoxin-positive M.haemolytica in the naso-pharynx from the onset of this study. It is likely that M.ovipneumoniae colonization predisposed this BHS to fatal infection with the M. haemolytica already present in this animal. The remaining three BHS developed pneumonia and died one to five days following intranasal inoculation with M.haemolytica. On necropsy, lungs of all four BHS showed lesions characteristic of bronchopneumonia. M.haemolytica and M.ovipneumoniae were isolated from the lungs. These results suggest that M.ovipneumoniae alone may not cause fatal pneumonia in BHS, but can predispose them to fatal pneumonia due to M.haemolytica infection.