The Pox in the North American Backyard: Volepox Virus Pathogenesis in California Mice (Peromyscus californicus)

Nadia F. Gallardo-Romero, Clifton P. Drew, Sonja L. Weiss, Maureen G. Metcalfe, Yoshinori J. Nakazawa, Scott K. Smith, Ginny L. Emerson, Christina L. Hutson, Johanna S. Salzer, Jeanine H. Bartlett, Victoria A. Olson, Cody J. Clemmons, Whitni B. Davidson, Sherif R. Zaki, Kevin L. Karem, Inger K. Damon, Darin S. Carroll

Volepox virus (VPXV) was first isolated in 1985 from a hind foot scab of an otherwise healthy California vole (Microtus californicus). Subsequent surveys in San Mateo County, CA, revealed serological evidence suggesting that VPXV is endemic to this area, and a second viral isolate from a Pinyon mouse (Peromyscus truei) was collected in 1988. Since then, few studies have been conducted regarding the ecology, pathology, and pathogenicity of VPXV, and its prevalence and role as a potential zoonotic agent remain unknown. To increase our understanding of VPXV disease progression, we challenged 24 California mice (Peromyscus californicus) intranasally with 1.6 × 10(3) PFU of purified VPXV. By day five post infection (pi) we observed decreased activity level, conjunctivitis, ruffled hair, skin lesions, facial edema, and crusty noses. A mortality rate of 54% was noted by day eight pi. In addition, internal organ necrosis and hemorrhages were observed during necropsy of deceased or euthanized animals. Viral loads in tissues (brain, gonad, kidney, liver, lung, spleen, submandibular lymph node, and adrenal gland), bodily secretions (saliva, and tears), and excretions (urine, and/or feces) were evaluated and compared using real time-PCR and tissue culture. Viral loads measured as high as 2 × 10(9) PFU/mL in some organs. Our results suggest that VPXV can cause extreme morbidity and mortality within rodent populations sympatric with the known VPXV reservoirs.