Dennis K. Bideshi, Yves Bigot, Brian A. Federici and Tatsinda Spears
from: Insect Virology (Edited by: Sassan Asgari and Karyn N. Johnson). Caister Academic Press, U.K. (2010)
The family Ascoviridae was erected almost a decade ago to accommodate a number of large double-stranded DNA viruses that are pathogenic to larvae and pupae of lepidopterous insects, primarily in the family Noctuidae. Ascoviruses are unique among members of known viral families with regard to their ultrastructure and pathobiology, and among entomoviruses, their mode of transmission is unusual, as they are vectored by parasitoid wasps. Ascovirus virions, for example, exhibit a reticulate pattern when negatively stained, and mature virions are produced by an elaborate process that combines virogenesis and the generation of virion-containing vesicles that accumulate in the blood (haemolymph) of the infected host. The virion vesicles are formed by a novel apoptotic process in which ascoviruses rescue and convert apoptotic bodies into infectious virion factories. These virion vesicles essentially serve as reservoirs for horizontal transmission of ascoviruses to susceptible hosts by female parasitoid wasps during oviposition. Though the study of ascovirus molecular biology is still in its early stages, recent advances in ascovirus molecular genetics and proteomics are beginning to reveal insights into biochemical processes related to their novel structure, pathobiology, and evolutionary origin. In this chapter, a brief historical perspective on the recognition of ascoviruses as a new family of viruses is presented, after which we discuss their evolutionary origin based on molecular profiling of genome sequences and proteomics, and possible mechanisms of virogenesis and the resulting pathology read more ...