Virion Occlusion Research Articles

Replication and occlusion of a granulosis virus in larval and adult midgut epithelium of the western grapeleaf skeletonizer, Harrisina brillians

The histopathology of a granulosis virus (GV) isolated from the western grapeleaf skeletonizer, Harrisina brillians (Lepidoptera; Zygaenidae), was studied in histological sections and wet mounts of this species. In contrast to all other known GVs, the principal site of infection for this virus was the midgut epithelium. In fourth instars exposed to virus, infection resulted in almost complete destruction of the midgut epithelium and host death by 6 days post-treatment. Infected gut cells in both larvae and adults supported complete replication of the virus, including the production and occlusion of virions. After infection, epithelial cells detached from the basement membrane and sloughed into the midgut lumen. Many larvae developed a diarrhea 2 to 4 days after infection which contained feces highly infectious to other larvae. Electron microscopy confirmed the presence of intact GV in these feces. The meconium collected from adults which survived infection as larvae was also highly infectious. These results suggest that horizontal and vertical routes of transmission made possible by the replication of this GV in the midgut epithelium contribute substantially to its ability to spread quickly throughout and decimate populations of H. brillians. Despite its atypical biology, the physical characteristics of this GV were similar to those of other GVs. The occlusion bodies were granular in shape, approximately 150 × 300–400 nm in size, and contained virions of averaging 80 × 200 nm. The estimated size of the genome was 120 kb pairs based on fragments generated by digestion of the viral DNA with the restriction endonucleases EcoRI and HindIII.

Mosquito baculovirus: Sequence of morphogenesis and ultrastructure of the virion

The morphogenic sequence of a mosquito baculovirus differed from other baculoviruses in that nucleocapsids ca. 180 nm were formed routinely by cleavage of nucleocapsids as long as 1 μm. Additionally, in one type of envelopment nucleocapsids were enveloped by vesicles which subsequently dissociated. Prior to and during virion occlusion the envelope contracted along two-thirds of the nucleocapsid resulting in the virion being bulbous at one end. The mature virion consisted of an enveloped nucleocapsid with an amorphous, but distinct layer between the nucleocapsid and envelope.

Differentiation of Trichoplusia ni MEV and Autographa californica MEV by macrophage migration inhibition tests

The macrophage migration inhibition test (MMI), an in vitro correlate of delayed hypersensitivity, was found to be an effective means of differentiating Trichoplusia ni and Autographa californica multiple embedded nuclear polyhedrosis viruses (NPV). Peritoneal exudate cells from guinea pigs sensitized to virions of T. ni NPV demonstrated significantly different MMI when challenged with T. ni vs A. californica virions. Similarly, when virions of A. californica NPV were employed as the sensitizing antigen, different percentages of MMI were observed in the homologuus versus heterologous challenges. The susceptibility of the fall armyworm, Spodoptera frugiperda, to these two pathogens was very similar as revealed by a comparison of LD 50's, slopes, and fiducial limits of dose-mortality regression lines. In contrast, the cabbage looper, T. ni, was much more susceptible to A. californica NPV. The polyhedral sizes, shapes, and virion occlusion patterns of the two species of NPV were virtually indistinguishable.

Replication of a nuclear polyhedrosis virus in serially transferred insect hemocyte cultures

The nuclear polyhedrosis virus (NPV) of Lambdina fiscellaria somniaria, propagated in L. f. fiscellaria larvae, was found to infect two cell lines of Malacosoma disstria hemocytes. The two cell lines, IPRI 66 and IPRI 108, had previously been subcultured 25 times and 5 times, respectively. Three days after inoculation of the cultures, polyhedra were seen in the nuclei and rhomboidal crystalline inclusions, typical of this virus, were seen in the cytoplasm of cells. Replication of virus and occlusion of virions in polyhedra was confirmed in infected cultures by electron microscopy. Healthy L. f. fiscellaria larvae became infected when they were fed or injected intrahemocoelically with infected cultures. Microscopical examination of infected cultures, and larval infectivity tests, indicated that viral replication was greater in IPRI 108 cells than in IPRI 66 cells.

Occluded and free virions in midgut cells of Malacosoma disstria infected with cytoplasmic-polyhedrosis virus (CPV)

The proportion of occluded virions and free virions in infected midgut cells of Malacosoma disstria was determined at advanced stages (10 days) of cytoplasmic-polyhedrosis virus infection. In infected cells, less than 30% of the virions were occluded within polyhedral bodies, and more than 70% were found as free forms. In virus with uridine- 3H, it was found that free virions were labeled more quickly than those occluded in polyhedra. Occlusion of virions within the protein matrix of the polyhedral inclusion body did not occur until 5–10 hr after the appearance of free virions.