Laboratory Studies
Most poxvirus infections can be recognized clinically. The virions can be recognized with negative staining and electron microscopy.
Variola and vaccinia can be cultured in vitro on chorioallantoic membranes of eggs and in tissue culture. In suspected cases of smallpox, the public health authorities should be notified immediately and clinical samples processed in containment facilities.
Infections with poxviruses induce humoral responses that include hemagglutination inhibition (HI), complement fixing (CF), and neutralizing antibodies. In vaccinia cases, the HI, CF, and antibody titers decline over time.
Other Tests
Histological analysis of the nodular skin lesions can be performed.
Histologic Findings
The cutaneous lesions of smallpox begin with vascular congestion of the dermis associated with mononuclear (lymphocytes and monocytes) infiltration. Epidermal cells develop ballooning degeneration, and intraepithelial multiloculated vesicles develop by rupture of cellular membranes in the stratum spinosum. Cells develop cytoplasmic acidophilic inclusions known as Guarnieri bodies. The lesions of vaccinia and monkeypox follow a similar evolution.
The lesion of molluscum contagiosum consists of a localized area of hypertrophic and hyperplastic epidermis that extends down to the dermis and produces a nodule that rises above the skin. Individual epidermal cells are enlarged and contain a characteristic cytoplasmic inclusion of hyaline acidophilic material called a molluscum body. The center of the lesion consists of degenerating epidermal cells and keratin. Very little inflammation is present.
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Poxviruses. Following vaccination for smallpox, this patient with chronic lymphocytic leukemia developed vaccinia gangrenosum.
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Poxviruses. Following vaccination for smallpox, a patient with chronic lymphocytic leukemia developed vaccinia gangrenosum. The lesion was on the left shoulder. As the lesion progressed, the patient also developed evidence of dissemination. This image shows a vaccinia pustule on the foot.
