Out of the Reservoir: Phenotypic and Genotypic Characterization of a Novel Cowpox Virus Isolated from a Common Vole

Abstract

The incidence of human cowpox virus (CPXV) infections has increased significantly in recent years. Serological surveys have suggested wild rodents as the main CPXV reservoir. We characterized a CPXV isolated during a large-scale screening from a feral common vole. A comparison of the full-length DNA sequence of this CPXV strain with a highly virulent pet rat CPXV isolate showed a sequence identity of 96%, including a large additional open reading frame (ORF) of about 6,000 nucleotides which is absent in the reference CPXV strain Brighton Red. Electron microscopy analysis demonstrated that the vole isolate, in contrast to the rat strain, forms A-type inclusion (ATI) bodies with incorporated virions, consistent with the presence of complete ati and p4c genes. Experimental infections showed that the vole CPXV strain caused only mild clinical symptoms in its natural host, while all rats developed severe respiratory symptoms followed by a systemic rash. In contrast, common voles infected with a high dose of the rat CPXV showed severe signs of respiratory disease but no skin lesions, whereas infection with a low dose led to virus excretion with only mild clinical signs. We concluded that the common vole is susceptible to infection with different CPXV strains. The spectrum ranges from well-adapted viruses causing limited clinical symptoms to highly virulent strains causing severe respiratory symptoms. In addition, the low pathogenicity of the vole isolate in its eponymous host suggests a role of common voles as a major CPXV reservoir, and future research will focus on the correlation between viral genotype and phenotype/ pathotype in accidental and reservoir species. IMPORTANCEWe report on the first detection and isolation of CPXV from a putative reservoir host, which enables comparative analyses to understand the infection cycle of these zoonotic orthopox viruses and the relevant genes involved. In vitro studies, including whole-genome sequencing as well as in vivo experiments using the Wistar rat model and the vole reservoir host allowed us to establish links between genomic sequences and the in vivo properties (virulence) of the novel vole isolate in comparison to those of a recent zoonotic CPXV isolated from pet rats in 2009. Furthermore, the role of genes present only in a reservoir isolate can now be further analyzed. These studies therefore allow unique insights and conclusions about the role of the rodent reservoir in CPXV epidemiology and transmission and about the zoonotic threat that these viruses represent. C owpox virus (CPXV), a member of the genus Orthopoxvirus (OPV) in the Poxviridae family, is suspected to be widespread in Western Eurasian rodents, particularly vole species (1, 2). From the presumed reservoir hosts, spill-over infections to accidental hosts are regularly observed (3). The accidental hosts include domestic cats and also exotic animals in zoos, such as large felids and elephants, which regularly develop severe disease (3). As CPXV is a zoonotic virus, humans in direct contact wit...

Survey for zoonotic pathogens in Norway rat populations from Europe

“…For Rickettsia investigation, ear pinna tissue was used and DNA isolation was performed with the MagNa Pure LC total nucleic acid isolation kit (Roche Diagnostics, Mannheim, Germany). For OPV investigation, liver tissue was used for DNA isolation following a recently published protocol . For polyomavirus detection, DNA isolation was performed with GeneMATRIX tissue DNA purification kit (Roboklon, Potsdam, Germany) from spleen samples following the manufacturer's instructions.…”

“…The screening of spleen samples for rat PyV DNA and of liver samples for OPV‐specific DNA followed recently published protocols . The 215 bp long polyomavirus VP1‐encoding PCR products of 28 selected samples were sequenced using the BigDye terminator sequencing kit (Perkin Elmer, Waltham, MA) on an ABI 310 genetic analyser (Applied Biosystems, Foster City, CA) and compared with the recently described nucleotide and amino acid sequences …”

“…OPV‐specific antibodies were detected by using an indirect immunofluorescence assay according to Hoffmann et al …”

Cowpox virus infection from pet rat

“…Small rodents, such as voles and mice, are considered a natural reservoir. No transmission between humans has been reported so far [1][2][3].…”

“…Cowpox virus belongs to genera orthopoxvirus -a heterogeneous group of viruses that infect a broad spectrum of wild rodents and domestic animals, but seem to be restricted to the Old World [2,3].…”