COMPARATIVE PATHOGENICITY AND SEROGROUPING OF 3 WASHINGTON ISOLATES OF INFECTIOUS BURSAL DISEASE VIRUS

The pathology of three infectious bursal disease virus (IBDV) isolates of Washington poultry origin (WA-678, WA-770, and WA-994) and seven o ther known IBDV strains (SAL, D-78, MO, OH, Var-A, 2512, and IM) was s tudied in 3-week-old specific-pathogen-free chickens, Inoculation with IM and 2512 strains resulted in illness and death. No clinical signs or mortality were present with WA-678, WA-770, and WA-994. Macroscopic ally, bursae were swollen and gelatinous with occasional hemorrhages. Isolate WA-994 caused marked bursal atrophy. Isolate WA-678 elicited m oderate bursal pathology. Isolate WA-770 resulted in minimal atrophy. Strains IM and 2512 caused severe bursal atrophy, and strains Var-A an d D-78 caused moderate atrophy. Strains SAL, MO, and OH caused no demo nstrable bursal atrophy. Results of the cross-neutralization study sho wed that the three isolates were more closely related to serotype 1 th an to serotype 2 IBDV.