Experimental induction of hemorrhagic-aplastic anemia in chickens. I. Etiology.

Exposure to infectious bursal disease virus (IBDV) at 1 day old followed by inclusion body hepatitis virus (IBHV) inoculation at 36 days produced typical lesions of hemorrhagic-aplastic anemia syndrome (HAS). The lesions included severe anemia, widespread hemorrhages, and dermatitis. HAS could not be induced in the first 4 weeks of life in chickens inoculated at one day old with IBHV alone or in combination with IBDV. It was concluded that the immunosuppressive effects of IBDV failed to alter the pathogenicity of IBHV in chicks less than 4 weeks old. This resistance was considered to be age-related. Subcutaneous inoculation of day-old chicks with IBDV produced a more severe infection than did oral exposure. Serial passage of IBHV in day-old chicks had no significant effect on the viral pathogenicity.