The antigenic relationships of 12 strains of infectious bronchitis virus (IBV) were evaluated by a virus-neutralization procedure similar to that used in typing human rhinoviruses. Such a procedure consists of reciprocal neutralization tests performed by reacting 32-320 EID50 or plaque-forming units of virus with 20 antibody units of antiserum. Eight serologic groups were identified by chicken embryo assay, and 4 by plaque-reduction (90%). In general, serologic groupings were not distinct but reflected numerous intergroup relationships. The contrasting results exhibited by indicator systems are viewed as differences in the accuracy of the methods employed. It is suggested that before an IBV classification scheme can be proposed, agreement must be reached on the most suitable indicator system, techniques must be standardized, and reference viruses and antisera distributed to several institutions for comparison testing. In addition, cross-protection studies are needed to determine the importance of IBV serotypes and/or variants on vaccine efficacy.

The virus-neutralization (VN) test was found much more sensitive than the agar-gel precipitin (AGP) test for detecting prior exposure to infectious bursal disease (IBD). Many sera that were negative in the AGP test were found to have VN antibodies, and virtually all sera in a commercial flock were free of precipitin but had VN titers. VN titers varied widely on a flock basis, and revaccination of an 8-month-old flock through the drinking water did not alter the antibody titers. Inoculation of maternally immune chicks at 7 days of age with IBD virus resulted in a good serologic response by both the AGP and VN tests.

Attempts failed to infect Coturnix quail with infectious bursal disease (IBD) virus by exposure at 7, 14, 21, and 31 days old. There were no clinical signs or gross and microscopic changes in the bursa of Fabricius, and serologic tests and virus isolation attempts from cloacal swabs were negative. Turkeys of two breeds exposed to IBD virus at 6 or 8 weeks old showed no clinical signs or lesions in the bursa of Fabricius, and the virus could not be isolated from cloacal swabs. They did respond serologically, however, by developing both precipitin and virus-neutralizing antibodies.

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Eight viruses were isolated in embryonating eggs, from psittacine birds comprising a cockatiel, a budgerigar, 3 parrots, a love bird, and 2 rosellas. Initial attempts at isolation used 3 routes of embryo inoculation: yolk sac, allantoic sac, and chorioallantoic membrane (CAM). The most sensitive route was determined for 6 of the isolates by making comparative titrations by yolk sac, allantoic sac, and CAM routes of inoculation. In growth-curve studies of 6 of the isolates, virus concentration was determined daily for 5-6 days postinoculation in the CAM, allantoamnionic fluid, and liver. Peak virus concentrations appeared in about 72 hours. The embryonic lesions observed are described. Only one of the isolates hemagglutinated fowl red blood cells.