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

HSV-1 infection and pathogenesis in the tree shrew eye following corneal inoculation

Herpes simplex virus type I (HSV-1) infection causes inflammation in the cornea known as herpes simplex virus keratitis (HSK), a common but serious corneal disease. It is not entirely clear whether the virus during recurring infection comes from the trigeminal ganglia or the eye tissue, including the retina and ciliary ganglion. Because the tree shrew is closely related to primates and tree shrew eye anatomic structures are similar to humans, we studied HSV-1 corneal infection in the tree shrew. We found that HSK symptoms closely mimic those found in human HSK showing typical punctiform and dendritic viral keratitis during the acute infection period. Following the HSV-specific lesions, complications such as stromal scarring, corneal thickening (primary infection), opacity, and neovascularization were observed. In the tree shrew model, following ocular inoculation, the cornea becomes infected, and viral protein can be detected using anti-HSV-1 antibodies in the epithelial layer and retina neuronal ganglion cells. The HSV-1 transcripts, ICP0, ICP4, and LAT can be detected at 3 days post-infection (dpi), peaking at 5 dpi. After 2 weeks, ICP4 and ICP0 transcripts are reduced to a basal level, but the Latency Associated Transcripts (LATs) continue to accumulate. Interestingly, after the acute infection, we still detected abundant active HSV-1 in tree shrew eyes. Further, we found HSV-1 persistent in the ciliary ganglion and cornea. These findings are discussed in support of the tree shrew as a non-human primate HSK model, which could be useful for mechanistic studies of HSK.

Characteristics of the tree shrew gut virome

The tree shrew (Tupaia belangeri) has been proposed as an alternative laboratory animal to primates in biomedical research in recent years. However, characteristics of the tree shrew gut virome remain unclear. In this study, the metagenomic analysis method was used to identify the features of gut virome from fecal samples of this animal. Results showed that 5.80% of sequence reads in the libraries exhibited significant similarity to sequences deposited in the viral reference database (NCBI non-redundant nucleotide databases, viral protein databases and ACLAME database), and these reads were further classified into three major orders: Caudovirales (58.0%), Picornavirales (16.0%), and Herpesvirales (6.0%). Siphoviridae (46.0%), Myoviridae (45.0%), and Podoviridae (8.0%) comprised most Caudovirales. Picornaviridae (99.9%) and Herpesviridae (99.0%) were the primary families of Picornavirales and Herpesvirales, respectively. According to the host types and nucleic acid classifications, all of the related viruses in this study were divided into bacterial phage (61.83%), animal-specific virus (34.50%), plant-specific virus (0.09%), insect-specific virus (0.08%) and other viruses (3.50%). The dsDNA virus accounted for 51.13% of the total, followed by ssRNA (33.51%) and ssDNA virus (15.36%). This study provides an initial understanding of the community structure of the gut virome of tree shrew and a baseline for future tree shrew virus investigation.

The tree shrew as a model for infectious diseases research

Despite major advances in medicine, infectious diseases still pose a significant threat to humanity. Mammalian models of disease have proved extremely useful in adding to the understanding of infectious diseases and the development of prophylactic and/or therapeutic interventions. Arguably the most important considerations of any animal model are (I) the similarity of the model to humans with respect to anatomy, physiology, immunology and disease progression, and (II) the expense of conducting experiments using the model organism. Often the choice of a model represents a compromise between these factors. Here we review the Northern Tree shrew (Tupaia belangeri), or tupaia, as a useful model for the study of infectious diseases. Tupaias are non-human primates similar in size to squirrels that are indigenous to Asia. Their genome has been sequenced and, overall, shows relatively high similarity to humans. There is also a close homology of many aspects of tupaia biology with human biology. Importantly, from an infectious diseases viewpoint, tupaias are susceptible to infection with unadapted human pathogens and manifest clinical signs akin to human infections. Overall, the relatively small size of the tupaia, their homology to humans and their susceptibility to human pathogens make them a useful model for the study of infectious diseases.

Characterization of hepatitis E virus infection in tree shrew (Tupaia belangeri chinensis)

Background

Hepatitis E virus (HEV) is a major cause of hepatitis in developing countries and poses a threat to public health worldwide. Tree shrew (Tupaia belangeri chinensis) is a useful animal model in studies on hepatitis viruses, such as hepatitis B and C viruses. However, the use of this animal model for HEV research is yet to be developed.

Methods

Tree shrews were intravenously (IV) injected with swine genotype 4 HEV or infected by contact-exposure to IV infected tree shrews. RT-nPCR was performed to detect HEV RNA in the feces, tissues, and blood. HEV capsid protein in the different tissues was detected by Western blot and estimated by quantitative RT-PCR. Anti-HEV antibodies were determined by ELISA. Liver damages were evaluated by histopathologic examination and analysis of liver-specific enzymes activities.

Results

Both negative and positive strands of HEV RNA were detected in the feces of the HEV-infected or contact-exposed tree shrews 3–4 days post-inoculation. HEV RNA was detectable in the liver, spleen, kidneys, and bile. Virusemia developed in all the HEV-infected tree shrews. HEV capsid protein was expressed in the liver, spleen, and kidneys. The histological examination and analysis of liver-specific enzymes activities showed that HEV caused acute liver lesions in the tree shrews. Meanwhile, the infected tree shrews showed positive IgG and IgM antibodies.

Conclusions

Tree shrews are susceptible to HEV and may be useful animal models for HEV experimental infection studies on pathogenesis or preclinical drug development.

Herpes Simplex Virus 1 Infection of Tree Shrews Differs from That of Mice in the Severity of Acute Infection and Viral Transcription in the Peripheral Nervous System

Studies of herpes simplex virus (HSV) infections of humans are limited by the use of rodent models such as mice, rabbits, and guinea pigs. Tree shrews (Tupaia belangeri chinensis) are small mammals indigenous to southwest Asia. At behavioral, anatomical, genomic, and evolutionary levels, tree shrews are much closer to primates than rodents are, and tree shrews are susceptible to HSV infection. Thus, we have studied herpes simplex virus 1 (HSV-1) infection in the tree shrew trigeminal ganglion (TG) following ocular inoculation. In situ hybridization, PCR, and quantitative reverse transcription-PCR (qRT-PCR) analyses confirm that HSV-1 latently infects neurons of the TG. When explant cocultivation of trigeminal ganglia was performed, the virus was recovered after 5 days of cocultivation with high efficiency. Swabbing the corneas of latently infected tree shrews revealed that tree shrews shed virus spontaneously at low frequencies. However, tree shrews differ significantly from mice in the expression of key HSV-1 genes, including ICP0, ICP4, and latency-associated transcript (LAT). In acutely infected tree shrew TGs, no level of ICP4 was observed, suggesting the absence of infection or a very weak, acute infection compared to that of the mouse. Immunofluorescence staining with ICP4 monoclonal antibody, and immunohistochemistry detection by HSV-1 polyclonal antibodies, showed a lack of viral proteins in tree shrew TGs during both acute and latent phases of infection. Cultivation of supernatant from homogenized, acutely infected TGs with RS1 cells also exhibited an absence of infectious HSV-1 from tree shrew TGs. We conclude that the tree shrew has an undetectable, or a much weaker, acute infection in the TGs. Interestingly, compared to mice, tree shrew TGs express high levels of ICP0 transcript in addition to LAT during latency. However, the ICP0 transcript remained nuclear, and no ICP0 protein could be seen during the course of mouse and tree shrew TG infections. Taken together, these observations suggest that the tree shrew TG infection differs significantly from the existing rodent models.

IMPORTANCE

Herpes simplex viruses (HSVs) establish lifelong infection in more than 80% of the human population, and their reactivation leads to oral and genital herpes. Currently, rodent models are the preferred models for latency studies. Rodents are distant from primates and may not fully represent human latency. The tree shrew is a small mammal, a prosimian primate, indigenous to southwest Asia. In an attempt to further develop the tree shrew as a useful model to study herpesvirus infection, we studied the establishment of latency and reactivation of HSV-1 in tree shrews following ocular inoculation. We found that the latent virus, which resides in the sensory neurons of the trigeminal ganglion, could be stress reactivated to produce infectious virus, following explant cocultivation and that spontaneous reactivation could be detected by cell culture of tears. Interestingly, the tree shrew model is quite different from the mouse model of HSV infection, in that the virus exhibited only a mild acute infection following inoculation with no detectable infectious virus from the sensory neurons. The mild infection may be more similar to human infection in that the sensory neurons continue to function after herpes reactivation and the affected skin tissue does not lose sensation. Our findings suggest that the tree shrew is a viable model to study HSV latency.

Histopathological changes in the liver of tree shrew (Tupaia belangeri chinensis) persistently infected with hepatitis B virus

BACKGROUND

An animal model for HBV that more closely approximates the disease in humans is needed. The tree shrew (Tupaia belangeri) is closely related to primates and susceptible to HBV. We previously established that neonatal tree shrews can be persistently infected with HBV in vivo, and here present a six year follow-up histopathological study of these animals.

METHODS

Group A consists of six tree shrews with persistent HBV infection, group B consists of three tree shrews with suspected persistent HBV infection, while group C consists of four tree shrews free of HBV infection. Serum and liver tissues samples were collected periodically from all animals. HBV antigen and HBV antibodies were detected by ELISA and/or TRFIA. HBV DNA in serum and in liver biopsies was measured by FQ-PCR. Liver biopsies were applied for general histopathologic observation and scoring, immunohistochemical detections of HBsAg and HBcAg, and ultrastructural observation with electron microscope technique.

RESULTS

Hydropic, fatty and eosinophilic degeneration of hepatocytes, lymphocytic infiltration and hyperplasia of small bile ducts in the portal area were observed in group A. One animal infected with HBV for over six years showed multiple necrotic areas which had fused to form bridging necrosis and fibrosis, and megalocytosis. The hepatic histopathological scores of group A were higher than those of group B and C. The histopathological score correlated positively with the duration of infection.

CONCLUSIONS

Hepatic histopathological changes observed in chronically HBV-infected tree shrews are similar to those observed in HBV-infected humans. The tree shrew may represent a novel animal model for HBV infection.

Tupaia CD81, SR-BI, claudin-1, and occludin support hepatitis C virus infection

Hepatitis C virus (HCV)-related research has been hampered by the lack of appropriate small-animal models. It has been reported that tree shrews, or tupaias (Tupaia belangeri), can be infected with serum-derived HCV. However, these reports do not firmly establish the tupaia as a reliable model of HCV infection. Human CD81, scavenger receptor class B type I (SR-BI), claudin 1 (CLDN1), and occludin (OCLN) are considered essential receptors or coreceptors for HCV cell entry. In the present study, the roles of these tupaia orthologs in HCV infection were assessed. Both CD81 and SR-BI of tupaia were found to be able to bind with HCV envelope protein 2 (E2). In comparison with human CD81, tupaia CD81 exhibited stronger binding activity with E2 and increased HCV pseudoparticle (HCVpp) cell entry 2-fold. The 293T cells transfected with tupaia CLDN1 became susceptible to HCVpp infection. Moreover, simultaneous transfection of the four tupaia factors into mouse NIH 3T3 cells made the cells susceptible to HCVpp infection. HCVpp of diverse genotypes were able to infect primary tupaia hepatocytes (PTHs), and this infection could be blocked by either anti-CD81 or anti-SR-BI. PTHs could be infected by cell culture-produced HCV (HCVcc) and did produce infectious progeny virus in culture supernatant. These findings indicate that PTHs possess all of the essential factors required for HCV entry and support the complete HCV infection cycle. This highlights both the mechanisms of susceptibility of tupaia to HCV infection and the possibility of using tupaia as a promising small-animal model in HCV study.

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.

Elimination of UL56 gene by insertion of LacZ cassette between nucleotide position 116030 to 121753 of the herpes simplex virus type 1 genome abrogates intraperitoneal pathogenicity in tree shrews and mice

In order to investigate whether or not the UL56 gene is involved in those processes determining the viral pathogenicity and latency, a recombinant virus HSV-1-M-LacZ was constructed in which the DNA sequences between nucleotide position (np) 116030 and 121753 were replaced by the E. coli beta-galactosidase (LacZ) gene. This deletion spans from the carboxyterminus of UL55 (np 116030) to the second exon of IE110 (np 121753) eliminating UL56 and the variable region of the BamHI DNA fragment B which were implicated in intraperitoneal pathogenicity and latency. The host range and growth kinetics of the recombinant virus HSV-1 M-LacZ were comparable to the parental strain HSV-1 F. As expected it was found that HSV-1-M-LacZ lost its virulent phenotype and was not able to develop acute infection in animals. The state of the UL56 gene was investigated by determining the cDNA sequence of the UL56 gene transcript of HSV-1 F using PCR products obtained after amplification of the cDNA with oligonucleotide primers corresponding to the translational start and stop codons of this gene. This analysis revealed that the DNA sequence of the UL56 gene of HSV-1 F differed from those DNA sequences determined for the genomic DNA of HSV-1 strain 17. Between nucleotide position 116343 and 116344 two nucleotides -AG- are inserted which prolong the ORF of the UL56 gene to 233 amino acids with a predicted molecular weight of 30 kDa.

Expression of human immunodeficiency virus type 1 gag gene using genetically engineered herpes simplex virus type 1 recombinants

Infectious herpes simplex virus type 1 (HSV-1) recombinants were constructed by inserting the cDNA sequence of the human immunodeficiency virus type 1 (HIV-1) gag gene (from nucleotide position 675 [SacI] to 3859 [Asp718] of the cDNA sequences of HIV-1 strain BH-10) within the DNA sequences of the BamHI DNA fragment B of the genome of an apathogenic HSV-1 strain HFEM. This HSV-1 strain possesses a 4.1-kbp deletion within the BamHI DNA fragment B between 0.762 and 0.789 map units of the viral genome, which allows the insertion of at least 4 kbp of foreign genetic material into this particular region. The DNA sequences of the immediate early promoter (IE4) of HSV-1 that were inserted upstream from the gag gene were used as a promoter. The screening of 205 virus stocks derived from individual plaques revealed that 46 recombinant viruses harbor HIV-1 gag-specific DNA sequences. However, it was found that only six of the recombinant viruses are able to express the gag gene product of HIV-1. This indicates that the ratio of the positive recombination events is about 2.9%.

Replacement of the deletion in the genome (0.762-0.789 mu) of avirulent HSV-1 HFEM using cloned MluI DNA fragment (0.7615-0.796 mu) of virulent HSV-1 F leads to generation of virulent intratypic recombinant

The HFEM strain of HSV-1 is apathogenic for the tree shrew by the intraperitoneal (i.p.) route because of a deletion in the genome coordinates 0.762-0.789. Insertion of the MluI DNA fragment (coordinates 0.7615-0.789) cloned from HSV-1 strain F, which is pathogenic for the tree shrew, restored the i.p. pathogenicity to strain HFEM. The recombinant designated R-M1-C1 was highly pathogenic for the tree shrew, but slightly virulent for inbred mouse strain A. It thus appears that the viral DNA sequence involved in the i.p. pathogenicity of HSV-1 is located within the genome coordinates 0.761-0.796. This sequence is recognized differently by the cellular elements involved in HSV-1 infection in the tree shrew and the mouse.

Investigation of the virulence genes of herpes simplex virus 2 by experimental infection in vivo with defined intertypic recombinants of a virulent HSV-2 X an avirulent HSV-1

For determination of the gene loci for virulence and tropism of herpes simplex virus 2 (HSV-2) intertypic recombinants of HSV-1 strain HFEM and HSV-2 strain 3345 were screened for their pathogenicity in the tree shrew. HSV-1 strain HFEM is not pathogenic in the tree shrew and can be recovered as a latent virus only from the spleen of the animals; but HSV-2 strain 3345, the other parental virus of the recombinants, was found to be virulent for the tree shrew and colonized the ganglia of latently infected animals. No clinical pictures were observed when the animals were inoculated with HSV recombinants RS1(3), RB2(3), RB2(8), RB2(9), RB2(10), RB5(2), RB7(3), and RB7(7). It was found, however, that HSV recombinant RB5(0) is pathogenic for the tree show. Studies of the state of viral latency in the animals infected with these recombinants revealed that only HSV recombinant RB5(0) was able to persist as latent virus in the spleen of latently infected animals. The genome of recombinant HSV-RB5(0) contains DNA sequences of HSV-2 strain 3345 with two interruptions at 0.22-0.33 and 0.54-0.59 viral map units. In these regions of HSV-RB5(0), DNA sequences of HSV-strain HFEM at 0.26-0.33 and about 0.57-0.58 viral map units, respectively, had been recombined. The results obtained in this study indicate that the recombinant HSV-RB5(0) acquired the virulent phenotype (v+) from parental virus HSV-2 strain 3345 but lost the phenotype for colonizing the ganglia (g+). Furthermore, it acquired the phenotype of parental virus HSV-1 strain HFEM for persisting in a latent state only in the spleen (s+ and g-) of the latently infected animals.

Mapping of the deletion in the genome of HSV-1 strain HFEM responsible for its avirulent phenotype

To determine the exact map position of the deletion in the genome of HSV-1 strain HFEM, the Bam HI DNA fragment B of the HSV-1 strains HFEM, F, and of HSV-R-HFehx-C19 were cloned in the Bam HI site of the bacterial plasmid vector pAT153 and analysed in detail. Analysis of the insert of the three recombinant plasmids harbouring the Bam HI DNA fragment B of HSV-1 strain F (pHSF-B-B), HSV-1 strain HFEM (pHSHF-B-B), and recombinant HSV-R-HFehx-C19 (pHSR19-B-B) was performed using a variety of restriction enzymes and Southern blot hybridization. These comparative studies revealed that the HpaI DNA fragment P of the intact viral genome of HSV-1 strain F is not present in the genome of HSV-1 strain HFEM, indicating that the deletion in HSV-1 strain HFEM corresponds to this fragment, which spans the coordinates 0.762 to 0.790 of the HSV-1 DNA. The size of the deletion was found to be 4.1 kbp, corresponding to 2.7 Md.

Transduction of virulence in herpes simplex virus type 1 from a pathogenic to an apathogenic strain by a cloned viral DNA fragment

Herpes simplex virus (HSV) type 1 strain HFEM, the genome of which contains a deletion of about 4 kilobasepairs (kbp) between 0.7 and 0.8 viral map units, is apathogenic in the tree shrew when the animals are inoculated intravenously, intraperitoneally and/or subcutaneously. Similar results were obtained using Balb/c mice. Studies of the state of viral latency in animals infected with HSV-1 strain HFEM revealed that this strain was unable to colonize the ganglia of tree shrews. Infectious virus could be recovered only from the spleens of latently infected tree shrews. Thus, this system offers new opportunities for investigating the gene functions responsible for the virulence of HSV-1. Marker rescue experiments were performed by the contransfection technique using native DNA of HSV-1 strain HFEM and Bam H I DNA fragment B derived from the pathogenic HSV-1 strain F and cloned in a bacterial vector. A number of different intratypic recombinants were established in which the deleted region of HSV-1 strain HFEM had been repaired. The pathogenicity of these recombinants was examined in vivo. One of the recombinants (HSV-R-HFehx-C19) caused generalized and lethal herpes virus infection in juvenile and adult tupaias, indicating that the virulence of the pathogenic HSV-1 strain F can be transduced by the cloned Bam H I DNA fragment B to the apathogenic HSV-1 strain HFEM.