Epstein-Barr virus: clinical and epidemiological revisits and genetic basis of oncogenesis

Epstein-Barr virus (EBV) is classified as a member in the order herpesvirales, family herpesviridae, subfamily gammaherpesvirinae and the genus lymphocytovirus. The virus is an exclusively human pathogen and thus also termed as human herpesvirus 4 (HHV4). It was the first oncogenic virus recognized and has been incriminated in the causation of tumors of both lymphatic and epithelial nature. It was reported in some previous studies that 95% of the population worldwide are serologically positive to the virus. Clinically, EBV primary infection is almost silent, persisting as a life-long asymptomatic latent infection in B cells although it may be responsible for a transient clinical syndrome called infectious mononucleosis. Following reactivation of the virus from latency due to immunocompromised status, EBV was found to be associated with several tumors. EBV linked to oncogenesis as detected in lymphoid tumors such as Burkitt's lymphoma (BL), Hodgkin's disease (HD), post-transplant lymphoproliferative disorders (PTLD) and T-cell lymphomas (e.g. Peripheral T-cell lymphomas; PTCL and Anaplastic large cell lymphomas; ALCL). It is also linked to epithelial tumors such as nasopharyngeal carcinoma (NPC), gastric carcinomas and oral hairy leukoplakia (OHL). In vitro, EBV many studies have demonstrated its ability to transform B cells into lymphoblastoid cell lines (LCLs). Despite these malignancies showing different clinical and epidemiological patterns when studied, genetic studies have suggested that these EBV- associated transformations were characterized generally by low level of virus gene expression with only the latent virus proteins (LVPs) upregulated in both tumors and LCLs. In this review, we summarize some clinical and epidemiological features of EBV- associated tumors. We also discuss how EBV latent genes may lead to oncogenesis in the different clinical malignancie

Detailed analysis of the mRNAs mapping in the short unique region of herpes simplex virus type 1

We have analysed the mRNAs which map within the short unique (US) region of the herpes simplex virus type 1 (HSV-1) genome. US has a total length of 12979 base pairs (1) and is extensively transcribed with approximately 94% of the total sequence present in cytoplasmic mRNAs and 79% of the total sequence considered to be protein coding. There are several examples of overlapping functions and multiple use of DNA sequence within this region. US contains 12 genes (1) which are expressed as 13 mRNAs. Two of these mRNAs are thought to arise from the same gene since they differ only slightly in the positions of their 5' ends and probably specify the same polypeptide. 11 of the 13 mRNAs are arranged into four nested families with unique 5' ends and common 3' co-termini. The other two mRNAs have unique 5' and 3' ends

Alphaherpesviruses possess a gene homologous to the protein kinase gene family of eukaryotes and retroviruses

The US3 genes of herpes simplex virus serotypes 1 and 2, and the corresponding gene of varicella-zoster virus, encode proteins whose sequences are clearly homologous to members of the protein kinase family of eukaryotes and retroviruses. Similarity is most characteristic, and strongest, in an 80 residue region comprising part of the catalytic structure of the kinases. In this region the herpesvirus proteins are most like a yeast cell division control protein, and least like the retrovirus protein-tyrosine kinases. We consider that the herpesvirus proteins are probably involved in modulation of cellular processes during lytic infection, although other roles are also possible, for example in latent infection

Evolutionary comparisons of the S segments in the genomes of Herpes Simplex virus type 1 and Varicella-Zoster virus

The genomes of herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV) consist of two covalently joined segments, L and S. Each segment comprises an unique sequence flanked by inverted repeats. We have reported previously the DNA sequences of the S segments in these two genomes, and have identified protein-coding regions therein. In HSV-1, the unique sequence of S contains ten entire genes plus the major parts of two more, and each inverted repeat contains one entire gene; in VZV, the unique sequence of S contains two entire genes plus the major parts of two more, and each inverted repeat contains three entire genes. In this report, an examination of polypeptide sequence homology has shown that each VZV gene has an HSV-1 counterpart, but that six of the HSV-1 genes have no VZV homologues. Thus, although these regions of the two genomes differ in gene layout, they are related to a significant degree. The analysis indicates that the inverted repeats are evidently capable of large-scale expansion or contraction during evolution. The differences in gene layout can be understood as resulting from a small number of recombinational events during the descent of HSV-1 and VZV from a common ancestor

Topics in herpesvirus genomics and evolution

Herpesviruses comprise an abundant, widely distributed group of large DNA viruses of humans and other vertebrates, and overall are among the most extensively studied large DNA viruses. Many herpesvirus genome sequences have been determined, and interpreted in terms of gene contents to give detailed views of both ubiquitous and lineage-specific functions. Availability of gene sequences has also enabled evaluations of evolutionary relationships. For herpesviruses of mammals, a robust phylogenetic tree has been constructed, which shows many features characteristic of synchronous development of virus and host lineages over large evolutionary timespans. It has also emerged that three distinct groupings of herpesviruses exist: the first containing viruses with mammals, birds and reptiles as natural hosts; the second containing viruses of amphibians and fish; and the third consisting of a single invertebrate herpesvirus. Within each of the first two groups, the genomes show clear evidence of descent from a common ancestor, but relationships between the three groups are extremely remote. Detailed analyses of capsid structures provide the best evidence for a common origin of the three groups. At a finer level, the structure of the capsid shell protein further suggests an element of common origin between herpesviruses and tailed DNA bacteriophages

Diversity and conservation of invertebrates on the sub-Antarctic Prince Edward Islands

The Prince Edward Islands form a unique component of South Africa's natural estate. Here we present an overview of the diversity of the invertebrate fauna found on Marion and Prince Edward Islands and the conservation threats facing it. The invertebrate fauna at the islands is well known owing to a significant recent effort to sample the entire fauna, although the nematodes remain poorly known. Mite, insect and springtail assemblages differ considerably between habitats and these patterns support an earlier distinction made between the epilithic and vegetated biotopes. Seasonal variation in the abundances of the arthropods is the norm, although the form of this seasonality varies considerably between species and between habitats. From a regional perspective, the biogeographic affinities of the fauna remain enigmatic. Nonetheless, it seems likely that isolation has been an important contributor to local, indigenous species richness on Marion Island, and speciation has clearly contributed several endemic species to the fauna. Introduced insect species richness is more closely related to mean annual temperature and the number of humans occupying islands in the sub-Antarctic region, and this pattern is reflected locally in the distribution of indigenous and exotic springtails on Marion Island. The introduced species are common in warm, moist habitats, while the indigenous species prefer colder, drier sites. Local climate change, in step with global trends, seems set to have pronounced influences on the invertebrate fauna. Direct effects are likely to take the form of increased abundances of introduced species because of their shorter life cycles and greater fecundity compared to indigenous species, which tend to be long-lived with low reproductive output. Indirect effects are likely to be the result of changes in predation patterns of introduced house mice, and changes in plant communities precipitated by the spread of invasive vascular plants, which in turn have a marked influence on invertebrate assemblages. Undoubtedly the largest conservation threats at the island are the interactions between climate change, introduced species, and human use. In particular, climate change is likely to mean the ready establishment of alien species propagules, while increasing human use is likely to increase propagule pressure. Conservation of the invertebrates at the island will best be served by reduction in human use and stringent enforcement of the provisions of the management plan for these special nature reserves.Conference Pape