Clinical Case Review: Mannheimia haemolytica in Beef Cattle By: Jose Valles and Lisa Taylor, Production Animal Consultation Mannheimia haemolytica is a primary bacterial pathogen of bovine respiratory disease (BRD) in beef cattle and therefore causes significant economic loss for cattle operations through decreased cattle performance and health status. Previously known as Bacterium bipolare multicidum and Pasteurella haemolytica, this pathogen affects bovine and ovine populations worldwide. Mannheimia haemolytica is a Gram-negative coccobacillus belonging to the Pasteurellaceae family. It is non-sporeforming, non-motile and facultative anaerobic. There are 12 serotypes of M. haemolytica; serotype A1 is most commonly isolated from the lungs of BRD cases. There are two reasons why cattle get sick: 1) an overwhelming dose of a pathogen or 2) a suppressed immune system. Mannheimia haemolytica is a bacterium that normally inhabits the upper respiratory tract (nasal passages) of cattle without causing any negative health effects. However, when a calf ’s immune system is suppressed due to calf stress or a viral infection (IBR, BVD, etc.), the bacteria are able to colonize and cause disease in the lung after being inhaled. Virulence factors of the bacteria such as leukotoxin and lipopolysaccharide cause pulmonary tissue damage, resulting in BRD. Respiratory disease associated with M. haemolytica infection commonly follows stressful events such as a viral infection, changes in diet, changes in weather, commingling of cattle, long-duration transport and weaning. Proper management prior to shipping that reduces stress or improves immune status of beef cattle is important in preventing BRD in feeder cattle due to M. haemolytica. Cattle sick with BRD associated with M. haemolytica commonly exhibit clinical signs such as going off feed, depression, standing alone, difficulty breathing, fever, grunting, coughing, nasal discharge and weight loss (Figure 1). These symptoms may vary depending on the severity of the disease and if the calf has a case complicated another bacterial or viral infection (either primary or secondary). 20 pacdvms.com
Figure 1: Depression, anorexia, and poor tolerance to exercise are clinical signs of Mannheimia haemolytica infections.
Recommended medical examination of cattle suspect of M. haemolytica infection includes rectal temperature, lung auscultation, visual clinical signs, feed intake, water consumption and movement. Cattle with BRD should be treated as soon as possible and then be closely monitored and provided supportive care. The right cranial (towards head) lung lobe is the most commonly affected lung lobe in cattle BRD cases. Cattle affected by M. haemolytica commonly present acute fibrinous pleuropneumonia and cranial-ventral broncho-consolidation. This presents as a dark red area of the lung and the affected lung tissue is heavy and firm compared to the normal lung being spongy, pink and light. Common gross lesions found at necropsy include accumulation of fibrin, necrosis, and thrombosis of the lung lobes on the bottom/ front quadrant of the lungs. (Figures 2, 3) Presence of M. haemolytica in the lower respiratory tract can be confirmed with bacterial culture while the calf is alive or dead. Samples from live cattle can be collected by bronchoalveolar lavage, tracheal swab, or transtracheal wash. Tissue samples from the lung of a dead calf can be collected at necropsy and sent to a diagnostic laboratory for bacterial isolation. Nasal and tonsil swab samples may test
