Morphological and Molecular Characterization of a Cypovirus (Reoviridae) from the Mosquito Uranotaenia sapphirina (Diptera: Culicidae)

The first report of an occluded cytoplasmic insect virus was from the midgut epithelial cells of the silkworm Bombyx mori (16). The virus was subsequently identified as a cytoplasmic polyhedrosis virus (CPV) to distinguish it from the nuclear polyhedrosis viruses already recognized (27). CPVs are commonly isolated from insects, mainly from Lepidoptera and occasionally from Diptera or Hymenoptera, but only rarely from Coleoptera or Neuroptera (15). Cytoplasmic polyhedrosis viruses usually have a ten-segmented double-stranded RNA (dsRNA) genome and are classified as members of the genus Cypovirus within the family Reoviridae (14, 20). Different cypovirus “types” were initially identified on the basis of differences in the migration patterns of their genome segments during polyacrylamide gel electrophoresis, i.e., electropherotypes (22). Subsequent studies showed a good correlation between electropherotype and the grouping of strains on the basis of serological properties (18) or RNA cross-hybridization (17, 20). It has recently been shown that, in addition to the RNA migration patterns, nucleotide sequences, for example, those of genome segment 10 (Seg-10; the polyhedrin gene), can be used to distinguish different Cypovirus species (20). Sixteen Cypovirus species (types) are currently recognized, all from lepidopteran hosts (20). Numerous viruses (isolated before the recognition of the genus Cypovirus) from the larvae of 20 different species of mosquitoes (representing nine different genera) were identified as CPVs based on similarities to viruses from Lepidoptera (12). These similarities included virion structure, the presence of inclusion bodies (polyhedra), and chronic infection in the cytoplasm of midgut epithelial cells. There were also three reports of CPVs from the midgut epithelium of adult mosquitoes (7, 8, 11). However, there was no further biophysical or biochemical analyses of these mosquito cypoviruses. We report an analysis of the biology, morphology, and molecular characteristics of a new CPV isolate from the mosquito Uranotaenia sapphirina (UsCPV). The data generated demonstrate that UsCPV has a distinct electropherotype and represents a new Cypovirus species.