Experimental infection of young broiler chickens with eastern equine encephalitis virus and Highlands J virus

Two-week-old broiler chickens were experimentally infected with either eastern equine encephalitis (EEE) virus or Highland J (HJ) virus. Mortality rates were 24/30 (80%) in EEE-virus-inoculated chickens and 2/30 (7%) in HJ-virus-inoculated chickens. Chickens inoculated with EEE virus exhibited severe depression and somnolence on days 1-6 postexposure (PE), with 17/30 birds dying during this period. After day 6 PE, EEE-virus-inoculated chickens exhibited abdominal distention, depression, and growth retardation, and an additional seven chickens died. Pathologic changes in EE-virus-inoculated chickens dying on days 1-6 PE consisted of multifocal necrosis in the heart and liver, as well as lymphoid depletion and necrosis in the thymus, spleen, and bursa of Fabricius. Ascites, pericardial effusion, and right ventricular dilatation of the heart were the predominant lesions in chickens dying after day 6 PE. No clinical signs were observed in sham-inoculated controls or in most HJ-virus-inoculated chickens. Ascites, pericardial effusion, and multifocal myocardial necrosis were observed in 2/30 HJ-virus-inoculated chickens that died or were euthanatized after development of clinical signs. These findings indicate that both EEE virus and HJ virus are pathogenic for young chickens.