KBSH parvovirus: comparison with porcine parvovirus

In vitro exposure of preimplantation porcine embryos to porcine parvovirus

Early porcine embryos at the four- to eight-cell stage can be infected with either the virulent (NADL-8) or avirulent KBSH strain of porcine parvovirus (PPV) by microinjection or by incubation of embryos with virus. Treatment of embryos by microinjection of virus or incubation in media with virus did not significantly inhibit in vitro development of the embryos when compared with untreated controls. RNA-DNA hybridization was used to identify the presence of virus associated with embryos. It was found that PPV-DNA was present in viable embryos after microinjection of embryos with KBSH and NADL-8 strains of PPV and after incubation of embryos with KBSH strain. The data indicated the presence of replicative virus associated with viable porcine embryos.

Investigation of porcine parvovirus among persons with hemophilia receiving Hyate:C porcine factor VIII concentrate

BACKGROUND

Porcine clotting factor has been used for more than 15 years to treat severe bleeding episodes in persons with hemophilia who have antibodies to human clotting factor. In 1996, QC procedures revealed for the first time the presence of porcine parvovirus (PPV) in the product. This report describes an investigation to determine the extent of product contamination and to evaluate past recipients of porcine clotting factor (Hyate:C, Speywood Biopharm) for evidence of PPV infection.

STUDY DESIGN AND METHODS

Stored specimens from 22 lots of previously released Hyate:C were tested for the presence of PPV DNA by PCR and nested PCR assays. Serum specimens from 98 recipients of Hyate:C and 24 controls who did not receive Hyate:C were tested for PPV antibodies by an immunofluorescence assay.

RESULTS

PPV DNA was detected in product from 21 of the 22 lots of Hyate:C, primarily by nested PCR testing. In contrast, none of the serum specimens from the 98 Hyate:C recipients tested positive for PPV IgG antibodies.

CONCLUSION

The risk of human disease from percutaneous exposure to low levels of PPV seems to be low. Nevertheless, the theoretical risk of human infection with PPV has led to manufacturing changes, including PCR screening of all porcine plasma, which are designed to eliminate this risk.

A monoclonal antibody which recognizes cell surface antigen and inhibits porcine parvovirus replication

Monoclonal antibody technologies were applied to the study of early events in porcine parvovirus (PPV) infections in vitro. Balb/c mice were immunized with whole swine testicle cells and hybridomas were produced following fusion with myeloma cells. Resultant clones were screened firstly in an ELISA system, to detect monoclonal antibody recognition of swine testicle cells, and secondly, in a fluorescent antibody test to detect monoclonal antibody which inhibited production of PPV antigen. One clone, 1H11, which satisfied these screening requirements, recognized proteins present in cell lines both permissive and non-permissive for porcine parvovirus replication and inhibited the production of virus progeny of several PPV isolates. A linear staining pattern of cross-linked plasma membranes, indicative of monoclonal antibody binding at the cell membrane, was demonstrated by indirect immunofluorescence assays. In immunoblotting experiments, 1H11 recognized a polypeptide of approximately 40 kDa in size, present in both permissive and non-permissive cell lines.

The NS and capsid genes determine the host range of porcine parvovirus

Porcine parvovirus is an autonomous parvovirus which normally infects pigs and multiplies in porcine cells in vitro. In this report, we describe the properties of a variant designated P2, which has extended its host range to include canine cells. The variant was able to produce cytopathic effects (CPE) in canine cells, unlike the prototype NADL-2 strain. The variant also produced higher viral antigen and infectivity titers in canine cells than the NADL-2 strain, whereas both strains produced CPE and similar titers in porcine cells. Generation of recombinant plasmids between the P2 variant DNA and an infectious clone of NADL-2, and analysis of the properties of the virus stocks produced from these recombinant plasmids, indicated that two changes were necessary for this extension in the host range. One change was located in the nonstructural protein coding region and the other in the capsid coding region.

Restriction of porcine parvovirus replication in nonpermissive cells

Swine testicle (ST) cells and Madin-Darby canine kidney (MDCK) cells differ in their ability to support replication of porcine parvovirus (PPV). Viral replication events in ST cells, a permissive cell type, and MDCK cells, a nonpermissive cell type, were compared in an attempt to elucidate putative mechanisms of restrictive virus replication. Radiolabeled PPV bound to the cell surface of both cell types equally well and the binding was shown to be PPV specific, indicating that the restriction was not at the cell surface level. In contrast, profound differences in intracellular events in PPV replication were observed between these two cell types. Synthesis of viral DNA was limited in MDCK cells in that the percentage of cells with replicative-form DNA as determined by strand-specific probe in situ hybridization was approximately 100-fold lower in MDCK cells than in ST cells at the same multiplicity of infection. Northern (RNA) blot analysis, using oligonucleotide probes derived from both structural and nonstructural protein-coding regions of the PPV genome, revealed four PPV mRNA transcripts from infected ST cells. Comparatively, RNA species from the structural protein coding region were actively transcribed in MDCK cells, but synthesis of RNA species from the nonstructural protein coding region was negligible. Immunoprecipitation of viral polypeptides revealed the three characteristic structural polypeptides, VP1, VP2, and VP3, along with the nonstructural polypeptide, NS-1 from ST cells. In contrast, neither viral structural or nonstructural polypeptides nor progeny virions were produced from MDCK cells. The data suggest that mechanisms controlling permissiveness of cells to PPV infection are associated with the level of viral DNA replication, RNA transcription, and viral antigen expression but not absorption to the cell surface.

Replication of two porcine parvovirus isolates at non-permissive temperatures

Previous studies have shown that replication in vitro of the porcine parvovirus (PPV) isolate, KBSH, was restricted at 39 degrees C but not at 37 degrees C. In contrast, replication of the Kresse isolate was restricted at 37 degrees C but not at 39 degrees C. In this study, Kresse and KBSH isolates were passaged up to ten times in swine testicle (ST) cells at non-permissive temperatures, and at subsequent passage viral protein synthesis, viral DNA synthesis, and progeny virus were evaluated. KBSH became adapted for replication at 39 degrees C upon serial passages, displaying an appreciable increase in viral progeny, viral polypeptides, and viral DNA concentration. This finding was also observed with Kresse virus isolate continuously passaged at 37 degrees C. Neither isolate became adapted for replication at 32 degrees C. In an attempt to examine the effect of in vitro passage at non-permissive temperatures on pathogenicity in swine, KBSH passaged 10 times either at 37 degrees C or 39 degrees C was inoculated into swine fetuses. Two of four fetuses inoculated with 39 degrees C-passaged KBSH were dead and hemorrhagic or mummified. All four fetuses inoculated with 39 degrees C-KBSH contained viral antigen and viral DNA. In contrast, fetuses inoculated with 37 degrees C-passaged KBSH, or with cell culture fluid were normal in appearance. Viral antigen and viral DNA were not demonstrated in fetuses inoculated with 37 degrees C-KBSH or cell culture fluids. These findings suggest the possibility that the ability to replicate at 39 degrees C is associated with virulence in swine fetuses.

Temperature dependent replication of porcine parvovirus isolates

The replication of four porcine parvovirus isolates, NADL-8, NADL-2, KBSH, and Kresse, in swine testes cells were compared at temperatures of 32, 37, and 39 degrees C. Replication of the Kresse isolate was restricted at 32 and 37 degrees C as evidenced by progeny virus, virus polypeptide and viral DNA synthesis, but not at 39 degrees C. In contrast, replication of KBSH was restricted at 39 degrees C, but not at 37 or 32 degrees C. Findings from this study support the contention that replication of KBSH and Kresse isolates are temperature dependent.

Porcine parvovirus: replication in and inhibition of selected cellular functions of swine alveolar macrophages and peripheral blood lymphocytes

The ability of four isolates of Porcine Parvovirus (NADL-8, NADL-2, KBSH, and Kresse) to replicate in and affect the functions of swine peripheral blood lymphocytes and alveolar macrophages was studied in vitro. V-strand and C-strand viral DNA was present in both concanavalin A- and non-treated lymphocytes as well as alveolar macrophages following infection with all four isolates. Indirect fluorescent antibody assays on swine testis cells, inoculated with cell lysates of NADL-8-infected peripheral blood lymphocytes (both concanavalin A- and non-treated) and alveolar macrophages, indicated that these immune cells supported the production of progeny virus. The quantity of viral DNA and progeny virus was dependent upon the multiplicity of infection and length of time following infection. Infection of lymphocytes and alveolar macrophages with PPV was associated with a decrease in cell viability. Peripheral blood mononuclear cells and alveolar macrophages infected with any of the four isolates demonstrated reduced lymphocyte blastogenesis and non-Fc-mediated alveolar macrophage phagocytosis, respectively.

Nucleotide sequence and genome organization of canine parvovirus

The genome of a canine parvovirus isolate strain (CPV-N) was cloned, and the DNA sequence was determined. The entire genome, including ends, was 5,323 nucleotides in length. The terminal repeat at the 3' end of the genome shared similar structural characteristics but limited homology with the rodent parvoviruses. The 5' terminal repeat was not detected in any of the clones. Instead, a region of DNA starting near the capsid gene stop codon and extending 248 base pairs into the coding region had been duplicated and inserted 75 base pairs downstream from the poly(A) addition site. Consensus sequences for the 5' donor and 3' acceptor sites as well as promotors and poly(A) addition sites were identified and compared with the available information on related parvoviruses. The genomic organization of CPV-N is similar to that of feline parvovirus (FPV) in that there are two major open reading frames (668 and 722 amino acids) in the plus strand (mRNA polarity). Both coding domains are in the same frame, and no significant open reading frames were apparent in any of the other frames of both minus and plus DNA strands. The nucleotide and amino acid homologies of the capsid genes between CPV-N and FPV were 98 and 99%, respectively. In contrast, the nucleotide and amino acid homologies of the capsid genes for CPV-N and CPV-b (S. Rhode III, J. Virol. 54:630-633, 1985) were 95 and 98%, respectively. These results indicate that very few nucleotide or amino acid changes differentiate the antigenic and host range specificity of FPV and CPV.

Molecular comparisons of in vivo- and in vitro-derived strains of Aleutian disease of mink parvovirus

DNA from one cell culture-adapted and two pathogenic strains of Aleutian disease of mink parvovirus (ADV) was molecularly cloned into the vectors pUC18 and pUC19. The DNA from the two pathogenic strains (ADV-Utah I and ADV-Pullman) was obtained from virus purified directly from the organs of infected mink, whereas the DNA from the nonpathogenic ADV-G was derived from cell culture material. The cloned segment from all three viruses represented a 3.55-kilobase-pair BamHI (15 map units) to HindIII (88 map units) fragment. Detailed physical mapping studies indicated that all three viruses shared 29 of 46 restriction endonuclease recognition sites but that 6 sites unique to the pathogenic strains and 5 sites unique to ADV-G were clustered in the portion of the genome expected to code for structural proteins. Clones from all three viruses directed the synthesis of two ADV-specific polypeptides with molecular weights of approximately 57 and 34 kilodaltons. Both species reacted with sera from infected mink as well as with a monoclonal antibody specific for ADV structural proteins. Because production of these ADV antigens was detected in both pUC18 and pUC19 and was not influenced by isopropyl-beta-D-thiogalactopyranoside (IPTG) induction, their expression was not regulated by the lac promoter of the pUC vector, but presumably by promoterlike sequences found within the ADV DNA. The proteins specified by the clones of ADV-G were 2 to 3 kilodaltons smaller than those of the two pathogenic strains, although the DNA segments were identical in size. This difference in protein molecular weights may correlate with pathogenicity, because capsid proteins of pathogenic and nonpathogenic strains of ADV exhibit a similar difference.

Characterization and recombination mapping of an antigenic and host range mutation of canine parvovirus

A mutant of canine parvovirus (CPV) was derived after culture of a highly passaged isolate of CPV in the NLFK feline cell line. The virus (CPV-102/10) differed from the parental strain in its antigenic type when tested with a panel of neutralizing monoclonal antibodies, and in its relative ability to replicate in a dog cell line or in dogs. The mutant formed little replicative form DNA in the canine cells. Five single recombinants and two double recombinants between CPV-102/10 and a wild type CPV were constructed by digesting purified viral replicative form DNA with restriction enzymes, ligating the separated ends from the different strains, and examining the viruses isolated after transfecting the DNA into cell cultures. Analysis of the recombinant viruses showed that the mutation(s) determining both the antigenic and host range differences mapped between 64 and 73 map units in the genome, within the capsid protein gene. Sequencing the DNA from that region revealed differences of two adjacent amino acids, both resulting in nonconservative differences in the predicted amino acid sequences of the viruses. These results show that the ability of CPV to infect dogs or their cultured cells is determined, at least in part, by the conformation of the surface of the virus capsid.