Naturally-occurring right terminal hairpin mutations in three genotypes of canine parvovirus (CPV-2a, CPV-2b and CPV-2c) have no effect on their growth characteristics.

We have isolated 4 naturally-occurring strains of CPV in mainland China and have identified them as CPV-2, 2a, 2b and 2c genotypes according to their VP2 sequences which also revealed substitutions within their right terminal regions. To determine if these substitutions affected the growth characteristics of the 4 strains, we constructed plasmids based on their genomic sequences minus their right terminal sequences, with the latter replaced by a single right terminal region. Analysis of rescued recombinants showed that the substitutions within their natural right termini had no significant effect on their growth characteristics.

Growth characteristics of canine pathogenic viruses in MDCK cells cultured in RPMI 1640 medium without animal protein.

Madin Darby canine kidney (MDCK) cells were adapted to serum-free RPMI 1640 medium and used for cultivation of canine viruses. RPMI 1640 medium was supplemented with a soybean peptone, L-glutamine and antibiotics, so that the protein concentration was less than 5 microg/ml (RPMI/SP medium). The resulting adapted MDCK-SP cells showed steady growth after the twenty-eighth passage in RPMI/SP medium (MDCK-SP cell culture). Canine distemper virus, canine parvovirus, canine adenoviruses and canine parainfluenza virus, which are the principal components of canine combined virus vaccines, grew in the MDCK-SP cell culture as efficiently as the parental MDCK cells cultured in the conventional Eagle's MEM containing fetal bovine serum. Consequently, the use of MDCK-SP cell culture can make current canine vaccine products much safer, of higher quality and at lower cost.

Mapping of determinants of the host range for canine cells in the genome of canine parvovirus using canine parvovirus/mink enteritis virus chimeric viruses.

Feline panleukopenia virus (FPLV), mink enteritis virus (MEV) and canine parvovirus (CPV) are more than 98% similar in DNA and predicted amino acid sequences, but they show different host-cell specificities; CPV is able to replicate in canine cells in culture, whereas FPLV and MEV cannot or replicate only to a low titre. To map the genomic region responsible for the host range of CPV in vitro, CPV/MEV chimeric viruses were generated by transfecting infectious CPV/MEV chimeric plasmids into a cultured feline kidney cell line, and their host cell ranges were analysed. The 60 to 91 map units (m.u.) region of the CPV genome, which contains a part of the capsid protein (VP) gene encoding from amino acid 91 (in the VP2 sequence) to the carboxy terminus of VP protein, was required to impart the ability to replicate in canine cells to MEV, although the chimeric virus containing the 60 to 91 m.u. region of the CPV genome in the MEV background did not replicate in canine cells as efficiently as did CPV derived from the infectious plasmid of CPV. Not only the VP gene, but also a part of the NS gene of CPV were considered to participate in the full expression of the ability to replicate in canine cells. Within the 60 to 91 m.u. region, five of nine amino acid changes between MEV-Abashiri and CPV-Y1 were thought to be phylogenetically CPV-common; however, a recombinant virus containing all five amino acid changes of CPV in the MEV background replicated minimally in canine cells.