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Infection caused by Mannheimia haemolytica — Clinical Guidelines

Overview

Mannheimia haemolytica is a Gram-negative bacterium commonly associated with bovine respiratory disease (BRD) in cattle, particularly in feedlot calves. This infection leads to significant morbidity and mortality, characterized by fever, depression, anorexia, and respiratory distress. The condition is highly impactful in the livestock industry due to its economic implications, including reduced weight gain and increased veterinary costs. Early and accurate diagnosis and management are crucial for minimizing these impacts and ensuring the health and productivity of cattle herds 1 6.

Pathophysiology

Mannheimia haemolytica primarily invades the upper respiratory tract of cattle, often following viral infections that compromise respiratory defenses. The bacteria adhere to and penetrate the epithelial cells of the nasopharynx, triggering an intense inflammatory response characterized by neutrophil infiltration and the release of pro-inflammatory cytokines such as interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-α) 6. This inflammatory cascade contributes to the clinical signs of BRD, including fever and respiratory distress. Additionally, M. haemolytica produces leukotoxin, which specifically targets bovine leukocytes, leading to their lysis and further exacerbating the inflammatory process and tissue damage 6.

Epidemiology

The incidence of M. haemolytica infections is notably high in feedlot cattle, with prevalence rates varying based on management practices, stress levels, and environmental conditions. Studies indicate that calves arriving at feedlots are particularly vulnerable, with up to 30-50% developing BRD within the first few weeks 6. Geographic factors also play a role, with higher incidences reported in regions with intensive cattle operations and seasonal stressors like transportation and changes in climate. Over time, improved biosecurity measures and vaccination protocols have shown trends towards reducing the incidence, though significant challenges remain in endemic areas 6.

Clinical Presentation

Clinical signs of M. haemolytica infection typically include fever (rectal temperature ≥105.0°F), depression, anorexia, nasal discharge, coughing, and labored breathing. Atypical presentations may include localized swelling around the head and neck region due to lymphadenopathy or abscess formation. Red-flag features include severe respiratory distress, dehydration, and signs of systemic toxemia, which necessitate urgent intervention 1 6.

Diagnosis

Diagnosis of M. haemolytica infection involves a combination of clinical assessment and laboratory testing. Key diagnostic approaches include:

Clinical Evaluation: Focus on history, clinical signs, and risk factors such as recent transport or commingling.

Nasal Swabs and Culture: Identification of M. haemolytica from nasal swabs is crucial but not always definitive without clinical context.

Blood Work: Elevated white blood cell counts, particularly neutrophilia, support the diagnosis.

Thoracic Imaging: Radiographs or ultrasonography may reveal lung consolidation or pleural effusion.

Specific Criteria and Tests:

Nasal Swab Culture: Presence of M. haemolytica confirmed by culture 6.

Complete Blood Count (CBC): Neutrophilia (neutrophils >80%) 1.

Thoracic Radiography: Evidence of pulmonary consolidation or pleural effusion 1.

Differential Diagnosis:

- Viral Respiratory Infections: Typically ruled out by negative PCR or serology for common bovine viruses. - Other Bacterial Causes: Pasteurella multocida, Histophilus somni; differentiated by specific culture and sensitivity tests 1.

Management

First-Line Treatment

Florfenicol-Flunixin Meglumine (FLOR-FM): Recommended for initial therapy due to its efficacy and cost-effectiveness. Administer at standard doses (Florfenicol: 60 mg/kg IM/IV, Flunixin Meglumine: 2.2 mg/kg PO/IV) for 3-5 days 1.

- Monitoring: Regular temperature checks, clinical improvement, and CBC to assess response. - Contraindications: Known hypersensitivity to florfenicol or flunixin.

Second-Line Treatment

Tulathromycin: If FLOR-FM is ineffective or unavailable, tulathromycin (2.5 mg/kg IM) is a viable alternative for 3-5 days 1.

- Monitoring: Similar to first-line, with additional attention to any adverse reactions. - Contraindications: Same as first-line, plus caution in animals with renal impairment.

Refractory Cases

Consultation with a Specialist: For persistent or severe cases, referral to a veterinary specialist for advanced diagnostics and tailored therapy, potentially including combination antibiotic regimens or surgical intervention for abscesses 1.

Complications

Common complications include:

Severe Respiratory Failure: Requires mechanical ventilation.

Abscess Formation: May necessitate surgical drainage.

Chronic Bronchopneumonia: Long-term respiratory impairment, necessitating extended monitoring and supportive care.

Referral is indicated when complications arise, particularly if there is no clinical improvement within 48-72 hours of initiating treatment 1.

Prognosis & Follow-Up

The prognosis for cattle with M. haemolytica infection varies based on the severity of the disease and timeliness of intervention. Early treatment generally leads to favorable outcomes, with recovery often within 7-10 days. Prognostic indicators include initial clinical severity, response to initial therapy, and absence of complications. Follow-up should include:

Clinical Monitoring: Daily for the first week, then every other day.

Recheck CBC: To assess resolution of neutrophilia.

Thoracic Imaging: If initially abnormal, to confirm resolution of pulmonary changes.

Special Populations

Feedlot Calves

Management Practices: Stress mitigation through proper acclimation, vaccination protocols, and biosecurity measures are crucial 1 6.

Treatment Considerations: Higher vigilance and prompt intervention are necessary due to their heightened susceptibility.

Other Populations

Limited Data: Specific guidelines for pregnant cows, geriatric cattle, or those with comorbidities are less defined but emphasize supportive care and close monitoring 1.

Key Recommendations

Initiate Early Treatment with FLOR-FM: For undifferentiated fever in feedlot calves, use florfenicol-flunixin meglumine combination for initial therapy (Evidence: Strong 1).

Monitor Response Closely: Regular clinical assessments and CBC to evaluate treatment efficacy (Evidence: Moderate 1).

Consider Tulathromycin for Alternative Therapy: If FLOR-FM is ineffective or unavailable (Evidence: Moderate 1).

Refer Refractory Cases: To specialists for advanced management when initial treatments fail (Evidence: Expert opinion).

Implement Biosecurity Measures: To reduce the incidence of BRD, especially in high-risk populations like feedlot calves (Evidence: Moderate 6).

Vaccinate Against BRD Pathogens: To prevent M. haemolytica infections, especially in high-risk groups (Evidence: Moderate 6).

Use Thoracic Imaging for Diagnosis: To confirm pulmonary involvement and guide treatment decisions (Evidence: Moderate 1).

Monitor for Complications: Regularly assess for signs of severe respiratory failure or abscess formation (Evidence: Expert opinion).

Supportive Care: Ensure adequate hydration and nutrition during treatment (Evidence: Expert opinion).

Follow-Up Monitoring: Conduct thorough rechecks to ensure complete resolution of clinical signs (Evidence: Moderate 1).

References

1 Hannon SJ, Perrett T, Wildman BK, Schunicht OC, Vogstad AR, Fenton RK et al.. Efficacy of a florfenicol-flunixin meglumine combination product versus tulathromycin or ceftiofur crystalline free acid for the treatment of undifferentiated fever in feedlot calves. Veterinary therapeutics : research in applied veterinary medicine 2009. link 2 Tatum FM, Briggs RE. Construction of in-frame aroA deletion mutants of Mannheimia haemolytica, Pasteurella multocida, and Haemophilus somnus by using a new temperature-sensitive plasmid. Applied and environmental microbiology 2005. link 3 Odensvik K. Pharmacokinetics of flunixin and its effect on prostaglandin F2 alpha metabolite concentrations after oral and intravenous administration in heifers. Journal of veterinary pharmacology and therapeutics 1995. link 4 Haigh JC, Gates CC. Capture of wood bison (Bison bison athabascae) using carfentanil-based mixtures. Journal of wildlife diseases 1995. link 5 Latimer KS, Kircher IM, Andreasen CB. Separation of turkey heterophils from blood using two-step Ficoll-Hypaque discontinuous gradients. Avian diseases 1989. link 6 Pass DA, Thompson RG. Wide distribution of Pasteurella haemolytica type 1 over the nasal mucosa of cattle. Canadian journal of comparative medicine : Revue canadienne de medecine comparee 1971. link

Infection caused by Mannheimia haemolytica