Guarnieri body

**Definition:** Guarnieri bodies are round to oval, eosinophilic, intracytoplasmic inclusions seen on histology (H&E) of infected skin/epithelial cells in smallpox (variola) and vaccinia infection. First described by Giuseppe Guarnieri (1892) in rabbit corneal cells inoculated with vaccinia/variola material.

**Pathophysiology:** - Poxviridae are large, enveloped, linear dsDNA viruses (brick-shaped/ovoid) that carry their own DNA-dependent RNA polymerase and replication machinery. Because of this, they replicate entirely in the host cell cytoplasm. - The Guarnieri body represents the cytoplasmic "viral factory" (viroplasm), where viral DNA replication and assembly occur. - Inclusions are of the type B (Guarnieri-type) variety, in contrast to type A inclusions, which are seen in cowpox and ectromelia.

**Clinical significance:** - Smallpox (variola major/minor): fever, prodrome, then centrifugal rash with deep-seated vesicles/pustules that are all in the same stage of development (monomorphic). This differs from varicella, which has a centripetal distribution and lesions in different stages. Transmission is by respiratory droplets. Smallpox was eradicated in 1980 (WHO); it remains a Category A bioterrorism agent. The vaccine uses live vaccinia virus. - Vaccinia: used in the smallpox vaccine. Complications include eczema vaccinatum, progressive vaccinia, and generalized vaccinia (contraindicated in immunocompromised patients). - Molluscum contagiosum (also a poxvirus): shows Henderson-Paterson bodies (large intracytoplasmic eosinophilic inclusions), not Guarnieri bodies.

**Inclusion body associations (high-yield):** - Guarnieri bodies: smallpox/vaccinia (cytoplasmic, eosinophilic) - Negri bodies: rabies (cytoplasmic, eosinophilic, in hippocampal pyramidal and cerebellar Purkinje cells) - Henderson-Paterson bodies: molluscum contagiosum - Cowdry type A: HSV, VZV, CMV (intranuclear) - Owl's eye: CMV (intranuclear, with cytoplasmic basophilic inclusions) - Councilman bodies: yellow fever/viral hepatitis (apoptotic hepatocytes) - Torres bodies: yellow fever (intranuclear) - Cowdry type B: adenovirus, poliovirus - Smudge cells: adenovirus - Warthin-Finkeldey cells: measles (multinucleated giant cells) - Intracytoplasmic inclusion: Chlamydia trachomatis (Halberstaedter-Prowazek bodies)

**Board pearl:** Poxviruses are the only DNA viruses that replicate in the cytoplasm. Guarnieri bodies = cytoplasmic eosinophilic inclusions = smallpox/vaccinia. Most other DNA viruses replicate in the nucleus.