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Cowpox virus (CPXV), a member of the genus Orthopoxvirus (OPV), has reservoirs in small mammals and may cause disease in humans, felidae and other animals. In this study we compared CPXVs isolated from humans and cats in Fennoscandia by restriction enzyme and DNA sequence analysis. The HindIII restriction profiles clearly distinguished geographically distinct CPXV isolates, whereas only minor differences were found between the profiles of geographically linked isolates. The complete gene sequences encoding the cytokine response modifier B, the hemagglutinin and the Chinese hamster ovary host range protein were determined for the same isolates and included in phylogenetic analysis. By including representative OPV sequences from GenBank, detailed comparative analyses were performed showing pronounced heterogeneity among CPXVs compared to members of other OPV species. However, a close relationship between the Norwegian (3 of 4 isolates) and Swedish isolates was detected, whereas the isolate from Finland was more closely related to a Russian isolate for all three genes compared. We infer that the investigated CPXVs have distinct evolutionary histories in different rodent lineages.

During the last decades, cowpox virus, a member of the genus Orthopoxvirus within the Poxviridae family, has appeared as a pathogen in domestic cats, zoo animal species, and humans. At the same time, vaccinia virus, another orthopoxvirus, has been used as a recombinant vaccine vector with foreign genes inserted in the thymidine kinase (TK) gene. By PCR and cycle sequencing, we have determined the nucleotide sequences of the TK gene and the A-type inclusion protein (ATIP) gene of virus isolates from two human cowpox cases in Sweden, as well as a human and a feline case from Norway. We also obtained the corresponding sequences from ectromelia virus (strain Moscow), cowpox virus (strain Brighton) and vaccinia virus (strain Western Reserve). The new virus isolates differed from ectromelia virus and vaccinia virus, and were confirmed to be cowpox virus strains. Isolates originating from the same country had nearly identical TK sequences and fully identical ATIP sequences. They probably represent local geographical strains of cowpox virus.

We report the first isolation of cowpox virus from a domestic cat in Norway, and the first confirmed isolation of cowpox virus from a human case in Norway. These two Norwegian cowpox virus isolates, as well as two Swedish human isolates, were partially characterized and compared with each other and with cowpox virus Brighton and vaccinia virus strain Western Reserve. Restriction enzyme analysis of the genomes revealed differences between all six viruses examined, but suggested that the two Norwegian isolates are closely related, as are the two Swedish isolates. Restriction endonuclease digestion of genomic DNA demonstrated that one of the Swedish isolates and the two Norwegian isolates have larger genomes than vaccinia virus strain Western Reserve, but smaller than cowpox Brighton. All four Scandinavian isolates lacked a 72 base-pair region within the A-type inclusion body protein gene which is present in the prototype cowpox virus Brighton.