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.     

Time scale of Poxvirus evolution

Unlike in vertebrates and RNA viruses, the molecular clock has not been estimated so far for DNA viruses. The extended conserved central region (102 kb) of the orthopoxvirus genome and the DNA polymerase gene (3 kb) were analyzed in viruses representing several genera of the family Poxviridae. Analysis was based on the known dating of the variola virus (VARV) transfer from Western Africa to South America and previous data on the phylogenetic relatedness of modern West African and South American isolates of VARV. The mutation accumulation rate was for the first time estimated for these DNA viruses at (0.9–1.2) × 10^?6 substitutions per site per year. It was assumed that poxviruses diverged from an ancestor approximately 500,000 years ago to form the recent species and that the ancestor of the genus Orthopoxvirus emerged approximately 300,000 years ago and gave origin to the modern species approximately 14,000 years ago.     

Poxvirus fibromas on African hares.

Small dermal tumors were found on three African hares (Lepus capensis) in the Laikipia District, Kenya. Gross and histopathologic studies revealed similarities to the Shope's fibroma of wild rabbits in North America and fibromas of European hares. Histological examination of the African hare fibromas revealed intracytoplasmic inclusion bodies characteristic of poxviruses and poxvirus virions were demonstrated by electron microscopy of ultrathin sections. Attempts to propagate the virus in rabbit skin, embryonated chicken eggs and cell cultures were unsuccessful.     

Inhibition of Poxvirus Replication by Streptovaricin

A component of streptovaricin complex inhibits the replication of poxvirus. To be effective, the inhibitor must be introduced early in the replication cycle; it appears to inhibit early messenger ribonucleic acid synthesis by viral cores, thus interfering with all subsequent events. Neither of the two major components of the complex, streptovaricin A or C, was the active component.     

Poxvirus Proteomics and Virus-Host Protein Interactions

Summary: Studies of the functional proteins encoded by the poxvirus genome provide information about the composition of the virus as well as individual virus-virus protein and virus-host protein interactions, which provides insight into viral pathogenesis and drug discovery. Widely used proteomic techniques to identify and characterize specific protein-protein interactions include yeast two-hybrid studies and coimmunoprecipitations. Recently, various mass spectrometry techniques have been employed to identify viral protein components of larger complexes. These methods, combined with structural studies, can provide new information about the putative functions of viral proteins as well as insights into virus-host interaction dynamics. For viral proteins of unknown function, identification of either viral or host binding partners provides clues about their putative function. In this review, we discuss poxvirus proteomics, including the use of proteomic methodologies to identify viral components and virus-host protein interactions. High-throughput global protein expression studies using protein chip technology as well as new methods for validating putative protein-protein interactions are also discussed.     

Induction of Poxvirus Ribonucleic Acid Polymerases

Two distinct ribonucleic acid polymerase activities were induced in HeLa cells by poxvirus infection. These activities differ both in their properties and the time of their appearance after infection. One catalyzes the dAT (copolymer of deoxyadenylate and deoxythymidylate)-primed conversion of adenosine triphosphate and uridine triphosphate into an acid-insoluble product. This enzyme is detectable only if deoxyribonucleic acid synthesis has been blocked. In contrast, the accumulation of progeny genomes is a necessary condition for induction of the second enzyme. The latter activity, which is unmasked by detergent treatment, is found exclusively in maturing virus particles. The possibility that both enzymes are involved in transcribing the viral genome is discussed.     

Poxvirus Orthologous Clusters (POCs)

Poxvirus Orthologous Clusters (POCs) is a JAVA client-server application which accesses an updated database containing all complete poxvirus genomes; it automatically groups orthologous genes into families based on BLASTP scores for assessment by a human database curator. POCs has a user-friendly interface permitting complex SQL queries to retrieve interesting groups of DNA and protein sequences as well as gene families for subsequent interrogation by a variety of integrated tools: BLASTP, BLASTX, TBLASTN, Jalview (multiple alignment), Dotlet (Dotplot), Laj (local alignment), and NAP (nucleotide to amino acid alignment).     

Effect of Rifampicin on Poxvirus Protein Synthesis

Poxvirus strains differ with respect to the effect of rifampicin on viral protein synthesis. Rifampicin severely depressed vaccinia-directed protein synthesis but had little effect on the rate of cowpox-directed protein synthesis, including one late virus-induced enzyme. The spectrum of polypeptides synthesized in cowpox-infected cells was similar in the presence or absence of rifampicin except for one significant difference. After removal of rifampicin, viruslike particles assembled to some extent, even when protein synthesis was inhibited by cycloheximide. However, reversal was more extensive if protein synthesis was allowed.     

Feline immunodeficiency virus tropism

Feline immunodeficiency virus (FIV) induces a disease similar to acquired immunodeficiency syndrome (AIDS) in cats, yet in contrast to human immunodeficiency virus (HIV), CD4 is not the viral receptor. We identified a primary receptor for FIV as CD134 (OX40), a T cell activation antigen and costimulatory molecule. CD134 expression promotes viral binding and renders cells permissive for viral entry, productive infection, and syncytium formation. Infection is CXCR4-dependent, analogous to infection with X4 strains of HIV. Thus, despite the evolutionary divergence of the feline and human lentiviruses, both viruses use receptors that target the virus to a subset of cells that are pivotal to the acquired immune response. Further, we applied the new method for FIV receptor to Ebola virus entry factors with some modifications, and identified receptor-type tyrosine kinases, Axl and Dtk (members of Tyro3 family). Distribution of the molecules matches well with the Ebola virus tropism.     

The Poxvirus A35 Protein Is an Immunoregulator

It was shown previously that the highly conserved vaccinia virus A35 gene is an important virulence factor in respiratory infection of mice. We show here that A35 is also required for full virulence by the intraperitoneal route of infection. A virus mutant in which the A35 gene has been removed replicated normally and elicited improved antibody, gamma interferon-secreting cell, and cytotoxic T-lymphocyte responses compared to wild-type virus, suggesting that A35 increases poxvirus virulence by immunomodulation. The enhanced immune response correlated with an improved control of viral titers in target organs after the development of the specific immune response. Finally, the A35 deletion mutant virus also provided protection from lethal challenge (1,000 50% lethal doses) equal to that of the wild-type virus. Together, these data suggest that A35 deletion viruses will make safer and more efficacious vaccines for poxviruses. In addition, the A35 deletion viruses will serve as improved platform vectors for other infectious diseases and cancer and will be superior vaccine choices for postexposure poxvirus vaccination, as they also provide improved kinetics of the immune response.Poxviruses are large, complex viruses with a broad host range and worldwide distribution (30). Members of the family Poxviridae include variola virus, the causative agent of smallpox, which induced a fatality rate of approximately 30% and killed hundreds of millions of people before its eradication in 1980 (28). Currently, the most dangerous extant human-infecting poxvirus is monkeypox virus, which is commonly found in African rodents. Monkeypox virus causes a smallpox-like illness with a 10% fatality rate. A recent study showed that 1.7% of people in the Likouala region in Africa had monkeypox-specific immunoglobulin M (IgM), indicating a significant ongoing infection rate (25). An outbreak of a low-virulence strain of monkeypox virus occurred in the United States in 2003, causing more than 80 human infections and several hospitalizations (6). This outbreak raises concern that monkeypox virus could establish itself in wild-rodent populations in North America (34), thus creating a local zoonotic reservoir for this emerging pathogen. Of further concern are the facts that monkeypox is spreading more efficiently in humans (18, 24, 31) and that the current poxvirus vaccine is not universally protective against monkeypox infection (27). Both variola and monkeypox viruses are considered bioterrorism and biowarfare concerns and are category A select-agent pathogens. There are also other poxvirus infections that sporadically cause human outbreaks, including Cantagalo virus in South America (10, 41) and buffalopox virus in India (23), and the incidence of tanapox virus appears to be increasing (12, 43). Molluscum contagiosum poxvirus accounts for approximately 300,000 doctor visits each year in the United States alone (29). Thus, the study of virulence mechanisms in this group of viruses is important.The eradication of smallpox was accomplished through the use of the related vaccinia virus (VV) as a live-virus vaccine. Despite its phenomenal success, the public vaccination program was discontinued because of the high incidence of complications due to the virulence of wild-type VV. It is estimated that approximately 25% of the population should not receive this vaccine because of immunodeficiency, eczema, pregnancy, or heart disease (14, 21, 45). Safer vaccines are necessary to protect against emerging or released poxviruses. In addition, poxviruses are being used as platform vaccines for other diseases such as human immunodeficiency virus, malaria, and cancer because they induce a robust immune response and accommodate the insertion of large pieces of foreign DNA. It is therefore of great importance to identify poxvirus virulence genes in order to develop safer and more effective poxvirus vaccines. Replication-defective strains, such as Modified Vaccinia Ankara, have been used in an effort to reduce the risks associated with vaccination (8, 47), but the production of these viruses can be challenging, they require higher doses of vaccine, and their protective efficacy against poxvirus infections in humans is unknown. As poxviruses inhibit the activation of antigen-presenting cells and antigen presentation (26, 38), another way to construct a safer vaccine is to develop replication-competent vaccine strains that exclude immunosuppressive genes (3) while retaining protective antigenic epitopes (17, 32). We show herein that the A35R gene is an excellent candidate for removal from vaccine strains.The VV A35 gene is highly conserved in mammalian-tropic poxviruses, and a sequence identity search has revealed that the protein has little similarity to any other poxvirus protein or any nonpoxvirus protein, suggesting that this gene has an important and novel function (39). We have shown that the A35 gene is not required for viral replication in vitro but is required for full virulence in the mouse model (39).We therefore tested the effects of A35R on immune responses during infection in the mouse model and tested its protective efficacy against virulent challenge.     

红斑性肢痛症相关痘病毒血清免疫学特征的研究

本文从四个方面综合报道了红斑性肢痛症相关痘病毒(ERPV)血清免疫学特征的研究结果。血清学鉴定表明,ERPV为正痘病毒属内成员,但与正痘病毒属内成员痘苗病毒和鼠痘病毒具有中和抗原表位差异。流行性红斑性肢痛症患者血清中含有抗ERPV的中和抗体和抗ERPVA型包涵体IgG抗体,其检出率明显高于当地未发病者和美国人群的检出率。     

Poxvirus genome evolution by gene gain and loss

The poxviruses (Poxviridae) are a family of viruses with double-stranded DNA genomes and substantial numbers (often >200) of genes per genome. We studied the patterns of gene gain and loss over the evolutionary history of 17 poxvirus complete genomes. A phylogeny based on gene family presence/absence showed good agreement with families based on concatenated amino acid sequences of conserved single-copy genes. Gene duplications in poxviruses were often lineage specific, and the most extensively duplicated viral gene families were found in only a few of the genomes analyzed. A total of 34 gene families were found to include a member in at least one of the poxvirus genomes analyzed and at least one animal genome; in 16 (47%) of these families, there was evidence of recent horizontal gene transfer (HGT) from host to virus. Gene families with evidence of HGT included several involved in host immune defense mechanisms (the MHC class I, interleukin-10, interleukin-24, interleukin-18, the interferon gamma receptor, and tumor necrosis factor receptor II) and others (glutaredoxin and glutathione peroxidase) involved in resistance of cells to oxidative stress. Thus "capture" of host genes by HGT has been a recurrent feature of poxvirus evolution and has played an important role in adapting the virus to survive host antiviral defense mechanisms.     

Some Physiochemical Properties of Yaba Poxvirus Deoxyribonucleic Acid

Yaba tumor poxvirus deoxyribonucleic acid (DNA) has a density of 1.6905 in CsCl and its T(m) value in 0.015 m citrate in saline is 82.3. The guanine plus cytosine content estimated from these properties was taken to be 32.5 +/- 0.5%, a value 2 to 3% less than for DNA from other poxviruses reported to date.     

HIV receptors and cellular tropism

Viruses use specific cell surface receptors to bind to and subsequently gain entry into their host cells. Some retroviruses such as HIV-1 and HIV-2 utilize one receptor for high-affinity binding (CD4), and a separate coreceptor to mediate fusion of the viral envelope with the cell membrane (CCR5 or CXCR4). The identification of these receptors explains the cellular tropism of HIV, and hence its pathogenesis leading to immune deficiency (T-helper cell depletion), the wasting syndrome (macrophage infection), and dementia (microglia infection). HIV can infect cells by membrane fusion at the cell surface and by receptor-mediated endocytosis. Knowledge of the HIV receptors has led to practical developments such as inhibitory drugs, reasons for genetic resistance to infection, and should inform the judicious choice of candidate vaccines.