Summary Prevalence of canine parvovirus type 2 (CPV‐2) in Japanese dogs and genomic variations among the virus strains were examined. Two‐step polymerase chain reaction with double‐nested primer pairs designed in the NS and VP1/VP2 genes of CPV‐2 was developed for the detection of the viral genome in faecal samples. A total of 74 samples obtained from diarrhoeal house dogs between 1993 and 1995 were tested by the PCR. The virus‐positive rate was 54.1 %, showing that CPV‐2 is still involved in many cases of acute infectious diarrhoea in Japanese dogs. The VP1/VP2 gene of the positive samples was subjected to restriction fragment length polymorphism (RFLP) analysis and nucleotide sequencing. RFLP patterns of the samples were almost identical to those of one CPV‐2 strain (TDKet‐91–42) isolated in 1991, but different from those of the CPV‐2 in the late 1970s and 1980s. The results suggest that a new genotype of CPV‐2 appeared and spread among Japanese dogs in the early 1990s.

Summary The polymerase‐chain reaction (PCR) and restriction‐fragment‐length‐polymorphism (RFLP) analysis were used to differentiate the wild‐ and vaccine‐type of canine parvovirus (CPV) in Japan. The entire coding region of the CPV genome was enzymatically amplified, and the PCR products of three wild strains and four vaccine strains were analysed using RFLP assay. Then, two polymorphic regions in the VP1/VP2 gene were selected to generate strain‐specific RFLP patterns. By using four restriction enzymes, wild and vaccine strains were clearly differentiated; only two vaccine strains, probably of the same origin, were indistinguishable from each other. The wild strains retained strain‐specific RFLP patterns throughout in vitro passage, and there was no diversity of RFLP patterns among the different lots of vaccine strains. A total of 21 recent field samples were tested, showing RFLP patterns identical to those of a wild strain isolated in 1991. These results suggest that the PCR‐RFLP analysis is a practical and reliable method of differentiating wild‐ and vaccine‐type CPVs.