Growth kinetics of Yaba tumor poxvirus after in vitro adaptation to cercopithecus kidney cells

Fast and reliable diagnostic methods for the detection of human poxvirus infections

Although the most prominent poxvirus, Variola virus, was successfully eradicated in the last century, several other poxviruses cause zoonotic infections that, in the early stages, resemble Variola virus infections with varying pathogenicity in humans. Over recent decades, numerous diagnostic methods for the detection of poxviruses have been established. As a result of technical progress and the advancement in molecular techniques, only a small selection of these methods meet the demands of being rapid and reliable. This review briefly introduces human poxviruses, summarizes the methods available, discusses their pros and cons and provides recommendations for a ‘fast and reliable diagnostic approach.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

Orf virus replication in bovine testis cells: kinetics of viral DNA, polypeptide, and infectious virus production and analysis of virion polypeptides

The replication of orf virus in bovine testis cells was analysed in one-step growth experiments. Newly replicated viral DNA was detected 4 to 6 hours post-infection (p.i.), accumulated rapidly between 8 and 16 hours p.i. and reached a plateau between 25 and 30 hours p.i. Most virus-induced polypeptides were first detected in a two hour period beginning 10 hours p.i., reached a peak rate of synthesis between 14 and 16 hours p.i., and continued at that rate for at least 10 hours. Host polypeptide synthesis declined to very low levels by 20 hours p.i. From these results, the transition between early and late events appears to occur between 8 and 10 hours p.i. Infectious virus was first detected between 16 and 18 hours p.i. and continued to be produced at a steady rate till 40 hours p.i. Up to 35 polypeptides were detected in SDS-polyacrylamide gels of purified orf virions disrupted in SDS/2-ME. Virions treated with NP40/2-ME were separable into soluble and insoluble components by centrifugation. Some 13 polypeptides were found in the soluble fraction and a polypeptide of molecular weight 38,500 believed to be the basic subunit of the virion surface tubule structure. Little difference was found between polypeptide profiles of five independently isolated NZ orf virus strains.

The morphogenesis of Yaba monkey tumor virus in a cynomolgus monkey kidney cell line

The morphogenesis of Yaba monkey tumor virus (YMTV) was investigated in a cynomolgus monkey kidney cell line. YMTV has been shown to grow less rapidly in high-passage cells (i.e., 65 passages) than in low-passage cells (i.e., between 30 and 60 passages). This prolonged growth cycle in high-passage cells allows for a more detailed analysis of the events in morphogenesis. Samples of YMTV-infected cells were prepared for analysis at 2, 3, 4, and 5 days postinfection. At least 12 "stages" of virus morphogenesis can be identified.

Biochemical and electron microscopic studies of the replication and composition of milker's node virus

Replication of milker's node virus (MNV) DNA begins 4 to 8 h postinfection, continues to 30 to 36 h postinfection in the cytoplasm of infected, primary bovine embryonic kidney cells, and is accompanied by an inhibition of host nuclear DNA synthesis. Between 20 and 24 h postinfection, newly replicated genomes are incorporated into particles which cosediment with purified MNV. These biochemical measurements could be correlated with the development of MN virions as revealed by electron microscopic analysis of thin sections prepared from infected cells. Analysis of the DNA in purified MNV showed that the virions contained a double-stranded DNA molecule with a molecular weight of 85 x 10(6) to 87 x 10(6) and a guanine-plus-cytosine content of about 63%. After denaturation and sedimentation analysis of MNV DNA in alkaline sucrose gradients, three major DNA species were resolved. These species appeared to represent intact, terminally cross-linked genomes (approximately 75 to 80S); genomes bearing one nick (or with one cross-link removed) (60 to 65S); and complementary, denatured DNA strands released from cross-linked genomes bearing two nicks (or with both cross-links removed) (52 to 55S). Forty [35S]methionine-labeled polypeptides, ranging from approximately 200,000 daltons to 10,000 to 15,000 daltons, were detected by radioautography after polyacrylamide gel electrophoresis of the proteins present in detergent-solubilized MNV preparations. Treatment of MN virions with Nonidet P-40, beta-mercaptoethanol, and sonication released 10 polypeptides, which were apparently located on the surface of virions. Further fractionation of these released polypeptides, followed by electron microscopy and polyacrylamide gel electrophoresis, indicated that a 42,000- to 45,000-dalton polypeptide is a major component of the threadlike tubule structure present on the surface of MN virions.

Nucleic acid synthesis in cytoplasm of Yaba monkey tumor virus-infected cells

Yaba tumor virus progeny appeared in cynomolgus monkey kidney cells at 24 h postinfection and reached a plateau at 72 h in the first cycle of replication. Viral DNA synthesis was first detected at about 3 h and reached a peak in 18 h. Maximum coating of viral DNA in infected cells occurred at 4 days postinfection. Rapidly labeled RNA was synthesized in the cytoplasm of virus-infected cells. At 6 h postinfection 7 to 10S RNA was present; this species was present in greater amount at 12 h; at 24 h a truncated peak indicated the presence of 14 to 15S as well as 7 to 10S RNA. Hybridization data indicated that the largest peak of messenger RNA synthesis occurred at 11 to 13 h postinfection and a second, slightly smaller, peak occurred at 21 to 23 h.

Inhibition of the synthesis of simian virus 40 antigens in cells preinfected with Yaba tumor virus

The synthesis of tumor and viral antigens after infection of an established line of cynomolgus monkey kidney cells with simian virus 40 (SV40) was compared in cells previously infected with Yaba virus and in cells not preinfected. SV40 failed to induce synthesis of tumor or viral antigens in cells preinfected with Yaba virus. The inhibitory state in preinfected cells was shown to develop sequentially. Increase in the rate of deoxyribonucleic acid synthesis in the nuclei of preinfected cells occurred after infection with SV40. This rate of increase was significantly lower than that which occurred in SV40-infected cells which had not been preinfected. Cytosine arabinoside did not exert significant effect on the development of the inhibitory effect against SV40 in Yaba virus-infected cells.

Simplified procedure for preparation of specific antibodies to gamma globulins

Antibodies were prepared to rhesus monkey, rabbit, dog, and hamster gamma globulins which had been purified by agar-block electrophoresis. Immunoelectrophoretic analysis demonstrated that these antisera were specific for gamma globulin components in whole serum. The use of these antisera as secondary serological reagents was examined.

Immunodiffusion analysis of Yaba poxvirus structural and associated antigens

Yaba poxvirus virions were extracted and purified from Rhesus monkey tumors. A saline-soluble virion fraction (Y-xp), obtained by mechanical fractionation of purified virions with an X-press, contained seven components in acrylamide gel electrophoresis; five of these components were reactive in immunodiffusion with whole virion and Y-xp antisera produced in rabbits and monkeys. The saline-insoluble residue remaining after X-press treatment was hydrolyzed with sodium dodecyl sulfate, urea, and 2-mercaptoethanol (SUM). This fraction, Y-sum, contained five components, four of which were demonstrable by immunodiffusion. There was no evidence of antigenic relationships between Y-xp and Y-sum antigens in immunodiffusion. In acrylamide gel electrophoresis, one Y-xp and one Y-sum component had similar mobilities. Y-xp but not Y-sum antisera contained viral-neutralizing antibodies. Virus-free saline extracts of Yaba tumor prepared with Genetron (YS) were essentially devoid of virion structural antigens. They failed to induce precipitating antibodies for virion antigens, were nonreactive in immunodiffusion with virion antisera, and gave low complement-fixation titers with virion antisera. Yaba virion antigens were recovered from the Genetron tumor sediment by SUM and alkaline hydrolysis. Antisera prepared to YS extracts gave a maximum of 17 precipitin lines in immunodiffusion with YS extracts; none was identified as a virion structural antigen. Saline extracts of tumor prepared without Genetron contained immunogenic amounts of 5 virion antigens and 12 to 14 associated antigens. Animals immunized with infected cell culture extracts (virus-free) formed antibodies to six to seven virion antigens. The implications of using extracts of Yaba poxvirus-infected tissues in complement-fixation tests to measure virion antibodies were discussed.