A Review on Pneumonic Pasteurellosis (respiratory Mannheimiosis) with Emphasis on Pathogenesis, Virulence Mechanisms and Predisposing Factors

Pneumonic pasteurellosis is one of the most economically important infectious diseases of ruminants with a wide prevalence throughout the continents. The disease is characterized by an acute febrile course with severe fibrinous or fibrinopurulent bronchopneumonia, fibrinous pleurisy and septicaemia. Infected animals may die within a few days of the onset of clinical signs, but those which survive the acute attack may become chronically infected. Mannheimia haemolytica is well established to be the major aetiological agent of the disease although Pasteurella multocida has also been incriminated in many acute outbreaks. Both Mannheimia and Pasteurella species are commensally resident in the respiratory tract of healthy ruminants and are capable of causing infection in animals with compromised pulmonary defense system. Hence, the disease is essentially triggered by physical or physiological stress created by adverse environmental and climatic conditions such as extremely bad weather, poor management, overcrowding, transportation or previous infection with respiratory viruses, mycoplasma or some other pathogenic organisms. In the present review, relevant aspects of pneumonic pasteurellosis are described and discussed in cattle, sheep and goats with more emphasis on pathogenesis, virulence mechanisms and predisposing factors.