Comparative pathogenicity and serogrouping of three 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 other known IBDV strains (SAL, D-78, MO, OH, Var-A, 2512, and IM) was studied 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. Macroscopically, bursae were swollen and gelatinous with occasional hemorrhages. Isolate WA-994 caused marked bursal atrophy. Isolate WA-678 elicited moderate bursal pathology. Isolate WA-770 resulted in minimal atrophy. Strains IM and 2512 caused severe bursal atrophy, and strains Var-A and D-78 caused moderate atrophy. Strains SAL, MO, and OH caused no demonstrable bursal atrophy. Results of the cross-neutralization study showed that the three isolates were more closely related to serotype 1 than to serotype 2 IBDV.