Pasteurella multocida infections are among the bacterial diseases that cause significant economic losses in cattle. First described at the end of the 19th century, this agent has been particularly associated with respiratory system diseases and has gradually been recognized as a critical component of the bovine respiratory disease complex. P. multocida is a Gram-negative, facultative anaerobic, capsulated coccobacillus. The bacterium is classified into five capsular types (A, B, D, E, and F). Among these, types A and B are most frequently isolated in cattle and are responsible for pneumonia and hemorrhagic septicemia. Contributing factors include immunosuppression and concurrent infections, with viral pathogens such as IBR, BRSV, and PI3 playing an important role alongside the immune status of the animal.

In pathogenesis, the bacterial capsule prevents phagocytosis, while lipopolysaccharides initiate inflammation and toxins contribute to tissue destruction. Colonization in the respiratory tract leads to pneumonia, whereas bacteremia combined with inadequate alveolar macrophage response results in hemorrhagic septicemia. Pathologically, fibrinous, hemorrhagic, and necrotic lesions are observed in the lungs. Clinical signs include fever, coughing, depression, anorexia, and nasal discharge, with sudden deaths occurring in peracute cases.

Diagnosis is based on bacteriological culture, serotyping, and PCR methods. Antibiotics such as tetracyclines, fluoroquinolones, and cephalosporins are effective, although antimicrobial resistance must be considered. In preventive medicine, vaccination is a fundamental approach, while the control of stress factors is equally important.

In conclusion, P. multocida infections pose a significant threat to respiratory health in cattle, with pathogenesis influenced by both environmental and immune-related factors, requiring a multidisciplinary approach for effective diagnosis and control.