Outbreak Investigation and Antimicrobial Resistance in Broiler Colibacillosis: A Case Report

Abstract

On July 23, 2025, a sudden outbreak characterized by respiratory distress, diarrhea, and increased mortality occurred in a four-week-old broiler flock at the University of Maiduguri Veterinary Teaching Hospital (UMVTH). The study aimed to determine the cause, antimicrobial resistance pattern, and effective control measures for the outbreak. Comprehensive diagnostic procedures were conducted, including clinical assessment, postmortem examination, bacteriological culture, serology, parasitology, and antimicrobial susceptibility testing. Blood, cloacal swabs, and tissue samples (liver, heart, spleen) were collected from affected and dead birds. Isolates were serotyped at the National Veterinary Research Institute (NVRI), Vom. Pure colonies of Escherichia coli exhibiting a metallic green sheen were isolated on Eosin Methylene Blue agar. Lesions consistent with colibacillosis, airsacculitis, fibrinous pericarditis (“bread and butter” appearance), hepatomegaly, splenomegaly, and pulmonary congestion were observed. Parasitological screening detected minimal coccidial oocysts and no helminths, while serology was negative for Infectious Bursal Disease and positive for protective Newcastle Disease titres, excluding major viral and parasitic co-infections. The isolates showed multidrug resistance to ampicillin, tetracycline, and sulfamethoxazole-trimethoprim but remained sensitive to ciprofloxacin. Serotyping confirmed avian pathogenic E. coli (APEC) serotypes O78, O2, and O1. Prompt diagnosis and targeted antimicrobial therapy effectively contained the outbreak. The findings highlight the significance of early laboratory investigation, strict biosecurity, and rational antimicrobial use to manage colibacillosis and limit the spread of resistant E. coli strains in poultry farms.