Serosurvey for orthopoxviruses in rodents and shrews from Norway

Two hundred and twenty one blood samples representing eight different rodent species and the common shrew (Sorex araneus), collected in Norway between 1993 and 1995, were examined for anti-orthopoxvirus antibodies by a competition enzyme linked imunnosorbent assay (ELISA) and, when possible, an indirect immunofluorescence assay. The serological results indicated that the bank vole (Clethrionomys glareolus), woodmouse (Apodemus sylvaticus) and Norway lemming (Lemmus lemmus) may be reservoir species for orthopoxviruses in Norway, with antibody prevalences of 17 (12/69), 30 (24/81) and 56% (19/34), respectively. Orthopoxvirus infection in lemmings has not been reported previously. On some other small rodent species such as field voles (Microtus agrestis), common rats (Rattus norvegicus), and common shrews, seropositive individuals were detected. However, the total number of tested animals was low, and the role of these species in the epidemiology of orthopoxvirus infections remains unclear. Attempts to isolate orthopoxviruses from these small mammals failed, although orthopoxvirus specific DNA sequences were detected previously in the same animals by the polymerase chain reaction (PCR). The serological results were compared with and discussed in the context of the occurrence of orthopoxvirus-specific DNA sequences, and it is concluded that orthopoxviruses are widely distributed among wildlife in Norway.