Cutaneous and systemic poxviral disease in red (Tamiasciurus hudsonicus) and gray (Sciurus carolinensis) squirrels

From September 2005 through October 2006, fibromatosis was diagnosed in 2 red squirrels (Tamiasciurus hudsonicus) and 1 gray squirrel (Sciurus carolinensis). All 3 squirrels had multifocal to coalescing, tan, firm alopecic cutaneous nodules. Two squirrels also had pulmonary nodules. Histologically, the cutaneous nodules had marked epidermal hyperplasia, with ballooning degeneration of keratinocytes, spongiosis, and eosinophilic cytoplasmic inclusions. The dermis was expanded by proliferation of atypical mesenchymal cells with cytoplasmic inclusions. Additional findings included pulmonary adenomatous hyperplasia with cytoplasmic inclusions, renal tubular epithelial hyperplasia with cytoplasmic inclusions, atypical mesenchymal proliferation in the liver, and atypical mesenchymal proliferation with cytoplasmic inclusions in the seminal vesicles. Ultrastructurally, poxviral particles were observed in skin scrapings and sections of cutaneous and pulmonary nodules. Polymerase chain reaction targeting the highly conserved Leporipoxvirus DNA polymerase gene was positive using DNA extracted from the cutaneous lesions of all 3 squirrels. Nucleotide sequence of the 390 base PCR amplicons was closely related to that of other members of the genus Leporipoxvirus. To the authors' knowledge, this is the first report of cutaneous and systemic poxviral disease in American red squirrels with molecular characterization of the squirrel fibroma virus.