The pathogenesis of pneumonia caused by Mannheimia haemolytica is not completely understood. In an ongoing series of studies, many bacterial components were found to induce pulmonary lesions including lipopolysaccharide, lipopolysaccharide-associated protein, and capsular polysaccharide. In ruminants, vaccination is important to prevent bacterial diseases.
Many veterinary vaccines are available but their effectiveness is questionable.
We have formulated effective vaccines, containing muramyl dipeptide, for caseous lymphadenitis in sheep and goats and M. haemolytica induced pneumonia in sheep and cattle. Not all animals exposed to M. haemolytica develop pneumonia and these differences may be related to innate pulmonary defense mechanisms. In 1992, pulmonary surfactant was found to be antimicrobial. Three, anionic peptides were then isolated. Minimal inhibitory concentrations of anionic peptides and similar analogs were comparable to that of other vertebrate antimicrobial peptides.