Parapoxviruses Workup

Updated: Apr 16, 2018
  • Author: Luke Bloomquist, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Laboratory Studies

Real-time polymerase chain reaction (PCR) of frozen tissue, vesicle material, or scab debris has a higher sensitivity than standard PCR and enables identification of not only the genus Parapoxvirus but also the specific species. [21, 22] This is not true of the other diagnostic tests available. This is of mostly academic importance in cases in which the affected individual may have had exposure to cattle as well as goats or sheep. Multiplex PCR and specific qPCR assays are also used for the detection and differentiation of parapoxviruses. [23]

Negative-stain electron microscopy (EM) of skin tissue allows direct visualization of the parapoxvirus; identification is based on the characteristic ovoid cross-hatched appearance of the virions. [24]

Serologic testing using serum antibody (IgM and IgG) levels can confirm parapoxvirus infection, but this test unable to distinguish the specific species.

Light microscopy and traditional histopathologic techniques may afford accurate identification of the characteristic cutaneous changes observed in a parapoxvirus infection, although histopathologic features are frequently nonspecific, particularly in later lesions.

Gram stain and bacterial culture are useful in cases in which Bacillus anthracis infection or bacterial superinfection is a concern.

If performed, complete blood cell count and C-reactive protein level are usually normal in uncomplicated parapoxvirus infection. [17]


Histologic Findings

Histologically, parapoxvirus infections are indistinguishable from one another.

Epidermal hyperplasia, mild acanthosis, parakeratosis, spongiform keratinocytic degeneration, and viral cytopathic changes occur, including cytoplasmic inclusion bodies and nuclear and cytoplasmic vacuolization. In the dermis, a dense mixed inflammatory infiltrate develops, consisting of mast cells, lymphocytes, polymorphonuclear leukocytes, eosinophils, and prominent upper-dermal edema. Prominent capillary dilatation and proliferation give the impression of an angiomatous dermal lesion. [11]

Later, histology shows a nonspecific ulcerative process. [25]