EFFECT OF INFECTION WITH HEMORRHAGIC ENTERITIS VIRUS ON SUSCEPTIBILITY OF TURKEYS TO ESCHERICHIA-COLI

The present study was designed to investigate hemorrhagic enteritis vi rus (HEV) as a predisposing factor influencing the susceptibility of y oung turkeys to Escherichia coli infections. In addition, the patholog ic changes caused by administration of E. coli by various routes were compared. Following oral infection with HEV, groups of turkeys were in oculated with various doses of pathogenic E. coli by intravenous (IV), intra-air sac (IA), or intratracheal (IT) routes. A synergistic effec t was observed in birds that were exposed to a combined HEV-E. coli ch allenge, resulting in higher mortality than that caused by either path ogen alone. This synergy was more evident when the bacteria were admin istered by the IT route than when it was administered by the two other routes. Turkeys infected with HEV and then inoculated IT with E. coli O78 had higher mortality (61%) and higher occurrence of gross body le sions (74%) than birds given E. coli alone (0% mortality and 16% gross lesions). After E. coli inoculation by the IA and IT routes, lesions observed were mainly pericarditis, perihepatitis, lung and air-sac les ions, splenic enlargement, and occasional arthritis. The incidence of lesions was affected by HEV exposure. In contrast, IV inoculation with E. coli O78 usually resulted in arthritis, and its incidence was inde pendent of previous HEV exposure. The synergistic effect between HEV a nd E. coli administered IT can be used as a challenge model for testin g E. coli vaccines.