''Orphan'' parvovirus (OPV) infection in laboratory mice and rats was
serologically surveyed for 465 mouse sera and 271 rat sera collected f
rom 1986 to 1987 and from 1993 to 1996 in Japan. The results suggest t
hat parvovirus infection is rare in mice but common in rats (positive
rate: 13-22%) and that most putative viruses were OPVs. OPV is therefo
re considered to already have been harbored for at least ten years in
Japan.