This chapter describes the Tetraviridae family. The virions of the Betatetravirus genus are nonenveloped, roughly spherical, of about 40 nm in diameter and exhibit T = 4 icosahedral shell quasi-symmetry. The genome consists of ssRNA and the viruses in the genus Betatetravirus have monopartite genomes. Betatetraviruses replicate in the cytoplasm and has three distinct types of genomic organization. Most of the members of the group are serologically interrelated but distinguishable. The majority of the isolates were identified on the basis of their serological reaction with antiserum raised against NβV. All the virus species were isolated from Lepidoptera species (moths and butterflies), principally from Saturniid, Limacodid, and Noctuid moths, and no replication in other animals has been detected. In larvae, virus replication is restricted predominantly to the cells of the midgut. With the exception of PrV, no infections by members of the Betatetravirus genus have been achieved in cultured cells, even when gRNA was transfected directly into cells. At high host densities, horizontal spread appears to be the major route of infection. Suggestive evidence exists for vertical transmission, which could be responsible for the observed persistence of tetraviruses within insect populations. The viruses replicate primarily in the cytoplasm of gut cells of several Lepidoptera species. The virons of omegatetravirus genus are nonenveloped, roughly spherical, about 40 nm in diameter and exhibit T = 4 icosahedral shell quasi-symmetry. Unlike viruses in the genus Betatetravirus, viruses in the genus Omegatetravirus have bipartite genomes. As with the betatetraviruses, omegatetraviruses replicate in the cytoplasm and studies in tissue culture cells show that the HaSV replicase is localized within the cytoplasm and associates with membranes derived from the endocytic pathway.
Tetraviridae