page_title: Baculoviridae
section_title: Baculovirus life cycle
hierarchical_section_title: Baculoviridae / Baculovirus life cycle
caption_attribution_description: English: Life cycle of w:Nuclear polyhedrosis virus (NPV)
context_page_description: Baculoviridae is a family of viruses. Arthropods, lepidoptera, hymenoptera, diptera, and decapoda serve as natural hosts. There are currently 84 species in this family, divided among four genera.
  Baculoviruses are known to infect invertebrates, with over 600 host species having been described. Immature forms of moth species are the most common hosts, but these viruses have also been found infecting sawflies, mosquitoes, and shrimp. Although baculoviruses are capable of entering mammalian cells in culture
  they are not known to be capable of replication in mammalian or other vertebrate animal cells.
  Starting in the 1940s they were used and studied widely as biopesticides in crop fields. Baculoviruses contain circular double-stranded genome ranging from 80 to 180 kbp.
context_section_description: The baculovirus life cycle involves two distinct forms of virus. Occlusion derived virus (ODV) is present in a protein matrix (polyhedrin or granulin) and is responsible for the primary infection of the host while the budded virus (BV) is released from the infected host cells later during the secondary infection.
  Baculoviruses have very species-specific tropisms among the invertebrates with over 700 host species having been described.  Immature (larval) forms of moth species are the most common hosts,  but these viruses have also been found infecting sawflies, mosquitoes, and shrimp.
  Typically, the initial infection occurs when a susceptible host insect feeds on plants that are contaminated with the occluded form of the virus. The protein matrix dissolves in the alkaline environment of the host midgut (stomach), releasing ODV that then fuse to the columnar epithelial cell membrane of the host intestine and are taken into the cell in endosomes. Nucleocapsids escape from the endosomes and are transported to nucleus. This step is possibly mediated by actin filaments. Viral transcription and replication occur in the cell nucleus and new BV particles are budded out from the basolateral side to spread the infection systemically. During budding, BV acquires a loosely fitting host cell membrane with expressed and displayed viral glycoproteins.
  Baculovirus infection can be divided to three distinct phases:
  Early (0–6 h post-infection),
  Late (6–24 h p.i.)
  Very late phase (18–24 to 72 h p.i.)
  While BV is produced in the late phase, the ODV form is produced in the very late phase acquiring the envelope from host cell nucleus and embedded in the matrix of occlusion body protein. These occlusion bodies are released when cells lyse to further spread baculovirus infection to next host.  The extensive lysis of cells frequently causes the host insect to literally disintegrate, thus the reason for the historic name "wilting disease." The complete ODV-polyhedrin particles are resistant to heat and light inactivation, whereas the naked BV virion is more sensitive to environment.
  When infecting a caterpillar, the advanced stages of infection cause the host to feed without resting, and then to climb to the higher parts of trees, including exposed places they would normally avoid due to the risk of predators.  This is an advantage for the virus if (when the host dissolves) it can drip down onto leaves which will be consumed by new hosts.
caption: Diagram of a NPV life cycle
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