Conventional diagnosis and metagenomic analysis of a novel co-infection case involving Escherichia coli and immunosuppressive conditions with petechial hepatitis of broilers in South Korea: a case report.

Abstract

BACKGROUND: The conventional diagnosis in poultry disease enhances accuracy by combining clinical and necropsy observation with various molecular biological analysis. However, if the causative agents of a disease are not isolated and detected, accurate diagnosis and future disease management become challenging. The purpose of the present study aimed to diagnose and identify the causes of disease in broilers with novel petechial hepatitis by applying metagenomic analysis. CASE PRESENTATION: Through the necropsy, tracheal and pericardial congestion, and severe petechia and perihepatitis in the livers were observed. Histopathological examination revealed infiltration of lymphocytes and bacterial colonies in various organs, as well as severe sinusoidal congestion, hemorrhages and hepatocyte necrosis in the livers. E. coli was isolated and identified in the liver samples. Although FAdV, CkChpV, CAstV, IBV and IBDV were detected, no viral agents were detected in the livers. Metagenomic analysis of the livers showed a predominance of bacterial composition, followed by fungal and viral agents, with E. coli being the most abundant. Analysis of virulence factors in E. coli revealed the presence of those associated with APEC, as well as other IPEC and ExPEC pathotypes. CONCLUSION: The present study identified a novel petechial hepatitis in broilers, associated with co-infections of antigenic variant IBDV, multiple pathotypes of E. coli, and possibly various causative. The application of metagenomic analysis proved valuable in identifying diverse potential pathogens when conventional methods were limited. These findings highlight the utility of metagenomic approaches as a complementary diagnostic tool and support their continued use in advancing poultry disease management.