Mannheimia haemolytica is a species of Gram-negative bacteria belonging to the family Pasteurellaceae. It is a facultatively anaerobic, non-spore-forming, and non-motile coccobacillus. M. haemolytica is a primary bacterial pathogen implicated in the bovine respiratory disease complex (BRDC), also commonly known as "shipping fever," particularly affecting cattle, sheep, and goats.
Mannheimia haemolytica was originally described as Pasteurella haemolytica by Newsom and Cross in 1932, based on bipolar organisms isolated from cases of pneumonia in sheep and cattle.[2] For decades, it was classified within the genus Pasteurella. However, advances in molecular taxonomy led to a reassessment of the [Pasteurella] haemolytica complex. In 1999, Angen and colleagues conducted a comprehensive study using DNA–DNA hybridization and 16S rRNA gene sequencing, which demonstrated sufficient genetic divergence to warrant creation of a new genus, Mannheimia.[3]
Pathogenesis
Mannheimia haemolytica primarily colonizes the upper respiratory tract of cattle and other ruminants but can become pathogenic under stress conditions such as transport, crowding, or viral infections. This bacterium secretes leukotoxins, endotoxins, and other virulence factors that damage respiratory tissues and impair host immunity, resulting in severe fibrinous pneumonia.[4]
Clinical signs
Affected cattle commonly exhibit symptoms such as fever, depression, reduced appetite, nasal discharge, coughing, and difficulty breathing. In severe cases, animals can rapidly progress to acute respiratory distress and death if untreated.[4]
Diagnosis
Diagnosis of Mannheimia haemolytica infection typically involves bacterial culture from nasal swabs, lung tissue, or bronchoalveolar lavage samples. Samples are commonly cultured on blood agar, where M. haemolytica forms characteristic β-hemolytic colonies. Confirmation is supported by biochemical tests and species-specific polymerase chain reaction (PCR) assays. In research and advanced diagnostic contexts, whole genome sequencing (WGS) is increasingly used to characterize isolates, monitor strain diversity, and investigate antimicrobial resistance.[5]
Preventative measures include vaccination programs targeting prevalent serotypes. Studies have shown that vaccines incorporating multiple serotypes, such as A1 and A6, or recombinant proteins like leukotoxin, can enhance protective efficacy.[7] In addition, good husbandry practices such as reducing stress, ensuring adequate ventilation, and avoiding overcrowding can reduce the risk of disease.[8]
↑ Newsom, I. E.; Cross, F. (1932). "Some bipolar organisms found in pneumonia in sheep". Journal of the American Veterinary Medical Association. 80: 711–719.
↑ Angen, Ole; Mutters, Rudolf; Caugant, Dag A.; Olsen, John E.; Bisgaard, Magne (1999). "Taxonomic relationships of the [Pasteurella] haemolytica complex as evaluated by DNA–DNA hybridizations and 16S rRNA sequencing with proposal of Mannheimia haemolytica gen. nov., comb. nov., Mannheimia granulomatis comb. nov., Mannheimia glucosida sp. nov., Mannheimia ruminalis sp. nov. and Mannheimia varigena sp. nov". International Journal of Systematic Bacteriology. 49 (1): 67–86. doi:10.1099/00207713-49-1-67. PMID10028248.
1 2 Rice, J. A.; Carrasco-Medina, L.; Hodgins, D. C.; Shewen, P. E. (December 2007). "Mannheimia haemolytica and bovine respiratory disease". Animal Health Research Reviews. 8 (2): 117–128. doi:10.1017/S1466252307001375. PMID18218156.
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