The diagnosis of vaccinia virus complications is usually straightforward and depends on obtaining the history of recent vaccinia virus exposure by vaccination or contact with a vaccinated individual. A careful workup for immune deficiency should be considered in patients who do not promptly improve.
The diagnosis of CNS complications is more difficult because the signs and symptoms are nonspecific. Although rare, postvaccinial encephalitis should be considered in any patient with neurologic symptoms developing 1-2 weeks after exposure to live vaccinia virus. Vaccinia virus has not been isolated from cerebrospinal fluid (CSF) of patients with encephalitis, and CSF analysis usually produces normal results, except for increased pressure; however, CSF analysis may be indicated to exclude other causes of encephalitis.
Imaging studies are not useful in the diagnosis of vaccinia infection or a postvaccinial complication, although imaging modalities may be helpful to exclude other causes of disease (eg, MRI of the brain in cases of suspected encephalitis).
Patients who present with skin manifestations usually have live viral particles replicating in the dermal lesions. The presence of vaccinia virus can be confirmed by obtaining a biopsy of the skin lesion and examination through microscopy, plaque titer assay, Western blot, and polymerase chain reaction (PCR) analysis.
Light microscopy may reveal characteristic inclusions (ie, Guarnieri bodies) in the cytoplasm of infected cells. This is distinct from the appearance of cells infected by viruses such as herpes simplex virus, which typically demonstrate intranuclear inclusion bodies.
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