A novel fish herpesvirus of Osmerus eperlanus

A herpesvirus of smelt (Osmerus eperlanus) was identified by thin section electron microscopy. Degenerated cells of skin lesions located on the back fin of smelt showed either intranucleic- or cytoplasmic herpesvirus-specific structures. In the nuclei "naked" virus capsids with a diameter of about 100 nm were observed. The diameter of the complete virion including its unilaterally extended envelope ranged from 200 to 350 nm. Remarkably, in complete virions the electron-opaque tegument is completely filling the region between nucleocapsid and envelope and as another unique feature the virion shows a "comet-shape" due to a long unilateral extension of its envelope. This kind of shape had been not reported for any of herpesviruses known so far. Consequently this virus was termed herpesvirus of Osmerus eperlanus (HVOE1) or Comet herpesvirus of smelt. Due to the long time storage at the nonstandard temperature of smelt virus the biological and genomic analysis of the HVOE1 was hampered. All attempts to study host range of HVOE1 failed as no virus replication was observed, indicating that infectivity was lost or the suitable cell culture was missing. The genomic DNA of HVOE1 was analyzed by DNA restriction endonucleases.

Analysis and characterization of the complete genome of tupaia (tree shrew) herpesvirus

The tupaia herpesvirus (THV) was isolated from spontaneously degenerating tissue cultures of malignant lymphoma, lung, and spleen cell cultures of tree shrews (Tupaia spp.). The determination of the complete nucleotide sequence of the THV strain 2 genome resulted in a 195,857-bp-long, linear DNA molecule with a G+C content of 66.5%. The terminal regions of the THV genome and the loci of conserved viral genes were found to be G+C richer. Furthermore, no large repetitive DNA sequences could be identified. This is in agreement with the previous classification of THV as the prototype species of herpesvirus genome group F. The search for potential coding regions resulted in the identification of 158 open reading frames (ORFs) regularly distributed on both DNA strands. Seventy-six out of the 158 ORFs code for proteins that are significantly homologous to known herpesvirus proteins. The highest homologies found were to primate and rodent cytomegaloviruses. Biological properties, protein homologies, the arrangement of conserved viral genes, and phylogenetic analysis revealed that THV is a member of the subfamily Betaherpesvirinae. The evolutionary lineages of THV and the cytomegaloviruses seem to have branched off from a common ancestor. In addition, it was found that the arrangements of conserved genes of THV and murine cytomegalovirus strain Smith, both of which are not able to form genomic isomers, are colinear with two different human cytomegalovirus (HCMV) strain AD169 genomic isomers that differ from each other in the orientation of the long unique region. The biological properties and the high degree of relatedness of THV to the mammalian cytomegaloviruses allow the consideration of THV as a model system for investigation of HCMV pathogenicity.

Isolation and molecular characterization of a novel cytopathogenic paramyxovirus from tree shrews

A cytopathic infectious agent was isolated from the kidneys of an apparently healthy tree shrew (Tupaia belangeri) that had been captured in the area around Bangkok. The infectivity was propagated in Tupaia fibroblast and kidney cell cultures. Paramyxovirus-like pleomorphic enveloped particles and helical nucleocapsids were observed by electron microscopy and accordingly the infectious agent was termed Tupaia paramyxovirus (TPMV). However, no serological cross-reactions were detected between TPMV and known paramyxoviruses. For the molecular characterization of TPMV an experimental strategy that allows the random-primed synthesis of relatively large cDNA molecules from viral genomic RNA was applied. Nucleotide sequence analysis of a TPMV-specific cDNA fragment (1544 bp) revealed two nonoverlapping partial open reading frames corresponding to paramyxoviral N and P transcription units. Using modified rapid amplification of cDNA ends techniques, a substantial contiguous portion of the viral genome (4065 nt) was elucidated including the complete N and P/V/C genes. The coding strategy of TPMV as well as significant amino acid sequence homologies clearly indicates an evolutionary relationship between TPMV and members of the genus Morbillivirus. Highest homologies were detected between TPMV and Hendra virus (equine morbillivirus), which recently emerged in Australia, causing outbreaks of fatal respiratory and neurological disease in horses and humans.

Molecular characterization and determination of the coding capacity of the genome of equine herpesvirus type 2 between the genome coordinates 0.235 and 0.258 (the EcoRI DNA fragment N; 4.2 kbp)

The complete DNA nucleotide sequence of the EcoRI DNA fragment N (0.235 to 0.258 viral map units) of equine herpes virus type 2 (EHV-2) strain T400/3 was determined. This DNA fragment comprises 4237 bp with a base composition of 55.23% G+C and 44.77% A+T. Nineteen open reading frames (ORFs) of 50-287 amino acid (aa) residues were detected. ORF number 10 is located between the nucleotide position 2220 and 2756 coding for a protein of 179 amino acid residues. This protein shows significant homology to the cytokine synthesis inhibitory factor (CSIF; interleukin 10) of human (76.4%) and mouse (68.5%), and to the Epstein-Barr virus (EBV) protein BCRF1 (70.6%). The existence of an interleukin 10 (IL-10) analogous gene within the genome of the EHV-2 was confirmed by screening the genome of nine EHV-2 strains using specific oligonucleotide primers corresponding to the 5' and 3' region of this particular gene by polymerase chain reaction. In all experiments an 870 bp DNA product was amplified. The specifity of the amplified DNA fragments obtained from individual EHV-2 strains was confirmed by DNA-DNA hybridization experiments. The DNA sequence analysis of the amplified DNA products of the EHV-2 strain LK was carried out. This analysis revealed the identity of the corresponding IL-10 gene (540 bp) of this strain to the IL-10 gene of EHV-2 strain T400/3. The presented data indicate that the EHV-2 genome harbors a viral interleukin 10-like gene. This is further evidence that the IL-10 gene can be present in the genomes of members of the Herpesviridae family.

Simian agent 8 (SA8): morphogenesis and ultrastructure

Electron microscopic studies on the morphogenesis of SA8 in primary rabbit brain cell cultures revealed that in early stages of infection, envelopment of nucleocapsids commonly occurred at the inner nuclear membrane. From the perinuclear space, enveloped virus particles moved into the cisternae of the endoplasmic reticulum (ER) in which they were transported, through the cytoplasm, to the plasma membrane. Alternatively, de-envelopment at the outer nuclear membrane and egress of naked capsids into the cytoplasm were frequently observed. Non-enveloped cytoplasmic capsids were also a consistent feature of cells in late stages of infection, when nuclear membranes became ruptured. In these cases, the envelopment of naked capsids took place by budding either into the cisternae of ER or into cytoplasmic vesicles and vacuoles, in which transport to and exocytosis at the cell membrane occurred. Budding at the cell membrane was rarely found. Capsids of enveloped particles were asymmetrically surrounded by an electron-dense layer which may be identical to the tegument. Because only enveloped cytoplasmic and free virions were tegumented we suggested that the tegumentation must occur during the envelopment (budding) into cytoplasmic vesicles and at the plasma membrane.

The diversity and unity of Herpesviridae

The family herpesviridae contains over 100 viruses endogenous to humans and to a wide variety of eukaryotic organisms. Inclusion in the family is based on architecture of the virion. The viruses differ significantly with respect to base composition and sequence arrangements of their DNAs, but share many biologic properties including the ability to remain latent in their hosts. On the basis of their biologic properties the herpesviruses have been classified into three subfamilies, i.e. alphaherpesvirinae, betaherpesvirinae and gammaherpesvirinae. The members of each subfamily share many properties including greater conservation and colinear arrangements of their genes. As a rule, more than one herpesvirus has been isolated from animals of economic importance and both humans have yielded viruses belong to all three subfamilies of the herpesviridae.

Concatemeric forms of intracellular Tupaia herpesvirus DNA

Kinetics of Tupaia herpesvirus strain 2 (THV-2) DNA synthesis was measured by labeling with radioactive thymidine and determining the amount of newly synthesized DNA. Viral DNA synthesis reached a maximum between 24 to 36 hr postinfection, preceded by a transient stimulation of host cell DNA synthesis. Blot hybridizations of labeled recombinant plasmids harboring inserts of both genomic termini of THV-2 and of individual viral terminal DNA fragments to DNA of virus-infected cells and combined restriction enzyme analysis of labeled intracellular viral DNA revealed the presence of linear concatemeric and/or circular viral DNA molecules.

Molecular cloning and physical mapping of the tupaia herpesvirus genome

Purified virion DNA of about 200 kilobase pairs of tupaia herpesvirus strain 2 was cleaved with EcoRI or HindIII restriction endonuclease. Restriction fragments representing the complete viral genome including both termini were inserted into the EcoRI, HindIII, and EcoRI-HindIII sites of the bacterial plasmid pAT153. Restriction maps for the restriction endonucleases EcoRI and HindIII were constructed with data derived from Southern blot hybridizations of individual viral DNA fragments or cloned DNA fragments which were hybridized to either viral genome fragments or recombinant plasmids. The analysis revealed that the tupaia herpesvirus genome consists of a long unique sequence of 200 kilobase pairs and that inverted repeat DNA sequences of greater than 40 base pairs do not occur, in agreement with previous electron microscopic data. No DNA sequence homology was detectable between the tupaia herpesvirus DNA and the genome of murine cytomegalovirus, which was reported to have a similar structure. In addition, seven individual isolates of tupaia herpesvirus were characterized. The isolates can be grouped into five strains by their DNA cleavage patterns.

Induction of generalized and lethal herpesvirus infection in the tree shrew by intrahepatic transfection of herpes simplex virus DNA

The infectivity of herpes simplex virus (HSV) genome was investigated in vivo using the tree shrew, which is highly susceptible to HSV, as an animal model. Individual tree shrews were inoculated intrahepatically with 0.2 ml of a transfection mixture containing 25 micrograms HSV DNA, 50 micrograms salmon sperm DNA, and 250 micrograms DEAE-dextran. Seven out of nine tree shrews transfected with HSV DNA developed a generalized herpesvirus infection. The new virus progeny was found in different organs of transfected animals.

Experimental infection and the state of viral latency of adult tupaia with herpes simplex virus type 1 and 2 and infection of juvenile Tupaia with temperature-sensitive mutants of HSV Type 2

The susceptibility of adult Tupaia Belangeri to infection with herpes simplex virus (HVS) was investigated. Adult animals were inoculated intraperitoneally with HSV type 1 or 2. With the exception of HSV-2, strain HG-52, 10(5)--10(6) PFU of all HSV strains caused lethal infection irrespective of the age of the animals. Infections HSV was recovered from the spinal cord of those animals which had survived infection with a low dose of virus. The DNA of the recovered viruses was compared to the DNA of the inoculated HSV. The viral genome of the recovered HSV was unchanged as judged by analysis of the fragment pattern of the viral DNA's using restriction endonucleases. Animals which had survived the first HSV infection were protected against a second infection even at highly lethal doses of HSV-1 or 2. Juvenile Tupaia survived infection with temperature-sensitive mutants of HSV-2, strain HG-52, which induced protection against a second infection with lethal doses of HSV-1 or 2.