Research Note: Electron-Microscope Characterization of Infectious Bursal Disease Virus

Infectious bursal disease (IBD) virus, an agent which causes necrosis lymphocytes of young chickens, was tentatively classified as a member of the reovirus group (1). The classification was based upon the morphology under ultrathin-section electron microscopy of the bursa of Fabricius from infected chickens (2,4,9,10), and upon limited biochemical characterization (3,5,6,12). No papers have yet been published on the virions of IBD virus. The present communication is confined to an electron-microscope study of negatively-stained preparation of IBD virus. The virus, strain GBF-1 isolated in this laboratory (6), was passaged 10 times in susceptible chickens. For preparation of partially purified IBD virus, typically affected bursae of Fabricius were harvested 4 days after inoculation, weighed, suspended 1:1 (wt/vol) with phosphate-buffered saline (PBS), PH 7.4, and homogenized in a Waring blender and Teflon homogenizer. The resulting homogenate was frozen and thawed 3 times. After slow centrifugation (5,000 rpm, 60 min) to remove cellular debris, the virus was concentrated by centrifugation at 40,000 rpm for 180 min with an angle-rotor ultracentrifuge Hitachi RP 40. The resulting pellet was suspended carefully in PBS by repeated pipetting. About 4.5 ml of this suspension was laid on 0.5 ml