[Pathohistological and ultrastructural studies of the nuclear polyhedrosis virus in the silkworm (Bombyx mori L.)]

Histopathologic studies were carried out on fifth instar silkworm moths of the Super 1 x Super 2 hybrid infected orally with Baculovirus bombycis along with ultrastructural investigations of the pathogen itself. It was found that the earliest changes in the moths set in at the 60th hour post inoculation. They consisted in the aggregation of chromatin, and the formation of polyhedral bodies in the fatty body, hypodermis, and peritracheal matrix; these appeared in the glandular tissue too, but not earlier than the 120th hour, while in the hemolymph they were found at the 40th hour. The morphogenesis of the virus was followed up via the electron microscope, giving a description of its structure. It was found to replicate in the viral plasma formed in the nuclei of the infected cells. First the nucleocapsids emerged which were enveloped in a two layer outer (developing) membrane while they were in the viral plasma or in the space between it and the nuclear membrane (the so-called ring zone). Then these tended to thoroughly enter the ring zone and incorporate randomly into the polyhedral bodies. The virions were enveloped at the rate of one in the developing membrane, rarely being up to five per envelope. It was assumed that both at induction and at artificial infection the process, resp., the virus replication runs its course after one and the same pattern. However, the number of virions in the developing membrane depends on the tissue in whose cells the virus is replicated.