Fusobacterium necrophorum in necrotic laryngitis of feedlot cattle

Necrotic laryngitis is an important cause of respiratory distress and economic loss in feedlot cattle.

Describe the clinical presentation, pathologic lesions, and microbiologic findings associated with necrotic laryngitis in feedlot steers.

Four 20-month-old feedlot steers diagnosed with necrotic laryngitis. Clinically affected steers exhibited inspiratory stridor, increased respiratory effort, and flared nares, indicative of upper airway obstruction.

Samples from inflamed nasopharyngeal tissues were collected endoscopically using guarded cytology swabs and submitted for culture, with concurrent blood collection for CBC and plasma and serum biochemistry analyses.

Endoscopic examinations identified laryngeal chondritis, mucopurulent diphtheritic membranes, and necrotic inflammation of the vocal folds. Aerobic cultures were negative, but anaerobic cultures yielded Fusobacterium necrophorum subsp. necrophorum and or F. necrophorum subsp. funduliforme. Hematologic evaluation indicated leukocytosis and increased plasma fibrinogen concentration, whereas serum biochemistry disclosed marked hyperglycemia and mild increases in hepatic enzyme activities, consistent with stress-related metabolic alterations. Antimicrobial susceptibility testing showed that F. necrophorum isolates were susceptible to β-lactams, tetracyclines, florfenicol, tiamulin, and trimethoprim/sulfamethoxazole, and resistant to aminoglycosides, fluoroquinolones, and with respect to macrolides, 4 strains were susceptible and 1 strain was resistant to tylosin, tilmicosin, and tulathromycin.

These findings indicate involvement of either F. necrophorum subsp. necrophorum or subsp. funduliforme in necrotic laryngitis of feedlot cattle. Observed antimicrobial susceptibility patterns indicate ongoing susceptibility to β-lactams and tetracyclines, supporting their continued use as first-line therapeutic options.