nucleopolyhedrovirus

Nucleopolyhedrovirus (NPV) refers to a group of large, double-stranded DNA viruses in the family Baculoviridae. NPVs infect insects, most commonly Lepidoptera, and are among the best studied baculoviruses. They are distinguished by the production of occlusion bodies, or polyhedra, in the nucleus of infected cells. Each polyhedron contains multiple mature virions and protects them in the environment until ingested by a new host.

In the infection cycle, two virion forms participate. Occlusion-derived virus (ODV) within each polyhedron initiates infection after oral uptake, typically in the gut epithelium of a larva. Budded virus (BV) is produced later and spreads the infection systemically within the host. The virus replicates in the nucleus, acquires an envelope, and assembles new ODVs and BVs for release. Release of occlusion bodies from dying hosts contaminates foliage, enabling transmission to new larvae.

Genomes of NPVs are large, circular or linear double-stranded DNA molecules, usually between about 80 and 180 kilobases, encoding roughly 80–180 genes. Gene content includes core baculovirus genes involved in replication, transcription, and virion assembly, as well as many host-interaction genes. The genome organization and number of occlusion bodies influence host range and environmental stability.

NPVs are used as biological control agents against pest insects because of their host specificity and environmental safety. They are also important research tools and are used in biotechnology, notably in the baculovirus expression vector system (BEVS) for producing recombinant proteins, using NPVs such as Autographa californica MNPV. Regulatory and ecological considerations guide their deployment and study.