Polyhedrosis

Polyhedrosis refers to diseases of insects caused by baculoviruses, a group of large DNA viruses in the family Baculoviridae. The hallmark of polyhedrosis is the production of occlusion bodies in infected cells: polyhedra in nucleopolyhedroviruses (NPVs) and granules in granuloviruses (GVs). These occlusion bodies protect virions in the environment and enable oral infection when ingested by a susceptible host, facilitating transmission.

Virology and life cycle: Baculoviruses are enveloped, with circular double-stranded DNA genomes. Infected larvae ingest occlusion bodies, which dissolve in the alkaline gut to release infectious virions. The virions initiate infection of midgut cells and spread systemically via budded virions. Late in infection, occlusion bodies form abundantly in nucleus and are released upon host death, contaminating the environment and enabling further infection of new hosts.

Hosts and disease signs: Polyhedrosis mainly affects Lepidoptera, though other insect orders can be hosts. Infected larvae typically show slowed growth, reduced feeding, lethargy, and eventual death. Infected material may exhibit a characteristic appearance and accumulate occlusion bodies, aiding field diagnosis.

Diagnosis and applications: Diagnosis relies on microscopy to detect occlusion bodies and molecular methods such as PCR. Baculoviruses are widely used as biological control agents against agricultural pests. Examples include granuloviruses like codling moth granulovirus (CpGV) and nucleopolyhedroviruses targeting various caterpillar pests. They are valued for host specificity and minimal non-target effects, though environmental persistence varies with formulation and conditions.

Research and safety: Baculoviruses serve as models for gene expression and biotechnology, including the production of recombinant proteins. They are considered safe for humans and non-target organisms when used appropriately.