Polyhedrosis

Definition

A viral disease of insects and other arthropods characterized by the formation of crystalline polyhedral occlusion bodies (polyhedra) in infected cells. These occlusion bodies, composed of viral particles embedded in a protein matrix, protect the virus in the environment and facilitate horizontal transmission between hosts. The disease typically causes cell lysis and tissue disintegration, often producing a characteristic symptom of liquefied, fragile cadavers.

Etymology

From Greek polyedros (many-faced) + -osis (disease condition), referring to the geometric, many-sided shape of the viral occlusion bodies

Example

Nuclear polyhedrosis virus (NPV) infections in caterpillars of the cabbage looper (Trichoplusia ni) produce large numbers of polyhedra in the cell nuclei, causing the larva to hang in an inverted 'V' posture before death and releasing millions of infectious occlusion bodies into the environment.

Related Terms

• occlusion body
• Nuclear polyhedrosis virus
• Cytoplasmic polyhedrosis virus
• baculovirus
• entomopathogenic virus
• virosis
• Biological control

Usage Notes

Distinguished from non-occluded viruses by the presence of polyhedral protein crystals. Nuclear polyhedrosis viruses (NPVs) form occlusion bodies in the nucleus, while cytoplasmic polyhedrosis viruses (CPVs) form them in the cytoplasm. The term is sometimes used specifically for diseases caused by baculoviruses (NPVs) or more broadly to include cypovirus (CPV) infections. Not all insect viral diseases produce occlusion bodies; those that do not (such as many iflaviruses) are not polyhedroses.