Extraneural localisation of herpes simplex virus in latently infected guinea pigs

Extraneuronal herpetic latency: animal and human corneal studies

HSV DNA has been previously detected by both in situ and dot blot hybridization in neuronal tissues latently infected with herpes simplex virus (HSV), but not in extraneuronal tissues. The present study, using dot blot hybridization with a cloned full-length HSV DNA probe and subtractive hybridization assays for detecting HSV RNA, reveals both the presence and activity of the HSV genome in 100% of HSV latently infected rabbit corneas tested. Studies on human herpetic corneas taken at keratoplasty using slot blot hybridization with a cloned full-length HSV DNA probe demonstrated positive binding (hybridization) to the probe in 50% of samples tested but no binding to normal human control DNA. These studies confirm earlier, less sensitive virus recovery assays and implicate the cornea as an extraneuronal site of HSV latency and reactivation.

Intrapreputial infection of young bulls with bovine herpesvirus type 1.2 (BHV-1.2): acute balanoposthitis, latent infection and detection of viral DNA in regional neural and non-neural tissues 50 days after experimental reactivation

Venereal infection of bulls with bovine herpesvirus type 1.2 (BHV-1.2) may result in acute balanoposthitis followed by the establishment of latent infection, presumably in dorsal root nerve ganglia. We herein report the characterization of the acute and latent infection of young bulls with a Brazilian BHV-1.2 isolate and the investigation of neural and non-neural sites in which viral DNA persists during latent infection, i.e. 110 days after inoculation and 50 days after experimental reactivation. Intrapreputial inoculation of BHV-1.2 isolate SV-56/90 (10(6.5)pfu per animal) resulted in severe balanoposthitis, characterized by redness of the penis and preputial mucosa, coalescent vesicles and fibrinous exsudate in all four infected bulls. Virus shedding was detected in preputial secretions and semen up to days 14 and 13 pi, respectively. Dexamethasone administration at day 60 pi led to reactivation of the infection in all animals, resulting in virus shedding in preputial secretions and/or in semen. At day 50 post-reactivation (pr), the animals were euthanized and regional tissues were collected for PCR and virus isolation. Viral DNA was consistently detected in the dorsal root ganglia of nerves genito-femoral (4/4) and obturator (4/4); frequently in the pudendal (3/4), sciatic (3/4) and rectal caudal nerve ganglia (2/3). In addition, viral DNA was detected in the pelvic sympathetic plexus of one bull and in regional lymph nodes (deep inguinal (2/4); sacral (1/4); medial iliac (1/4)) of two bulls. No infectious virus could be recovered from homogenates of DNA positive tissues, indicating the absence of actively replicating virus. These results demonstrate that BHV-1.2 DNA may persist in several sacral nerve ganglia and in regional lymph nodes as well during latent infection, i.e. 50 days after experimental reactivation. These findings may help in understanding the pathogenesis of acute and latent genital infection by BHV-1.2.

Distribution of bovine herpesvirus type 5 DNA in the central nervous systems of latently, experimentally infected calves

Bovine herpesvirus type 5 (BHV-5) is an alphaherpesvirus associated with meningoencephalitis, a disease highly prevalent in South America. In this study, we investigated the distribution of BHV-5 DNA in the brains of latently, experimentally infected calves by using a PCR for the glycoprotein B gene. Twelve calves inoculated intranasally with a Brazilian BHV-5 isolate were divided into two groups: group A calves (n = 4) were euthanized 55 days postinoculation (p.i.) for tissue collection; group B calves (n = 8) were submitted to dexamethasone administration at day 60 p.i. for reactivation of latent infection and were euthanized 50 days later. Latent infection was reactivated in all group B calves, as demonstrated by virus isolation from nasal secretions and/or seroconversion. Three calves developed neurological disease and died or were euthanized in extremis. For group A calves, viral DNA was consistently detected in the trigeminal ganglia (4/4), midbrain (4/4), thalamus (4/4), and olfactory cortex (4/4) and less frequently in the pons (3/4), cerebellum (3/4), anterior cerebral cortex (2/4), and olfactory bulb (2/4). For calves previously submitted to reactivation (group B), viral DNA was detected with roughly the same frequency in the same areas as for the group A calves. In addition, viral DNA was detected in the posterior (5/5) and dorso-lateral cortex (3/5). All DNA-positive tissues were negative for infectivity and viral antigens. These results demonstrated that latent BHV-5 DNA is present in several areas of the brain during latent infection and that virus reactivation may result in the establishment of latent infection in additional sites of the brain.

The transgenic ICP4 promoter is activated in Schwann cells in trigeminal ganglia of mice latently infected with herpes simplex virus type 1

Herpes simplex virus type 1 (HSV-1) establishes a latent infection in neurons of sensory ganglia, including those of the trigeminal ganglia. Latent viral infection has been hypothesized to be regulated by restriction of viral immediate-early gene expression in neurons. Numerous in situ hybridization studies in mice and in humans have shown that transcription from the HSV-1 genome in latently infected neurons is limited to the latency-associated transcripts. In other studies, immediate-early gene (ICP4) transcripts have been detected by reverse transcription-PCR (RT-PCR) in homogenates of latently infected trigeminal ganglia of mice. We used reporter transgenic mice containing the HSV-1(F) ICP4 promoter fused to the coding sequence of the beta-galactosidase gene to determine whether neurons in latently infected trigeminal ganglia activated the ICP4 promoter. Mice were inoculated via the corneal route with HSV-1(F). At 5, 11, 23, and 37 days postinfection (dpi), trigeminal ganglia were examined for beta-galactosidase-positive cells. The numbers of beta-galactosidase-positive neurons and nonneuronal cells were similar at 5 dpi. The number of positive neurons decreased at 11 dpi and returned to the level of mock-inoculated transgenic controls at 23 and 37 dpi. The number of positive nonneuronal cells increased at 11 and 23 dpi and remained elevated at 37 dpi. Viral proteins were detected in neurons and nonneuronal cells in acutely infected ganglia, but were not detected in latently infected ganglia. Colabeling experiments confirmed that the transgenic ICP4 promoter was activated in Schwann cells during latent infection. These findings suggest that the cells that express the HSV-1 ICP4 gene in latently infected ganglia are not neurons.

Is herpes simplex virus associated with pulp/periapical inflammation?

OBJECTIVES

This study focuses on the detection of herpes simplex virus (HSV) DNA in dental pulp and inflamed periapical tissue.

STUDY DESIGN

Dental pulp tissue (vital and necrotic) and periapical tissue samples were collected under strictly sterile conditions and examined for the presence of HSV DNA. Saliva samples were also examined for the presence of the viral DNA. The polymerase chain reaction assay was used to detect viral DNA. Blood samples were collected, and the enzyme-linked immunosorbent assay (ELISA) for immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies against HSV was carried out.

RESULTS

According to the ELISA test, 19 of the 23 blood samples were IgG-positive and IgM-negative to HSV, whereas 4 were IgG-negative and IgM-negative. HSV DNA was not detected in the tissue and the saliva samples tested.

CONCLUSION

HSV is not present and therefore is probably not involved in the pathology of tooth neural tissue.

Persistence and reactivation of bovine herpesvirus 1 in the tonsils of latently infected calves

Bovine herpesvirus 1 (BHV-1), like other members of the Alphaherpesvirinae subfamily, establishes latent infection in sensory neurons. Reactivation from latency can occur after natural or corticosteroid-induced stress culminating in recurrent disease and/or virus transmission to uninfected animals. Our previous results concluded that CD4(+) T cells in the tonsil and other adjacent lymph nodes are infected and undergo apoptosis during acute infection (M. T. Winkler, A. Doster, and C. Jones, J. Virol. 73:8657-8668, 1999). To test whether BHV-1 persisted in lymphoreticular tissue, we analyzed tonsils of latently infected calves for the presence of viral DNA and gene expression. BHV-1 DNA was consistently detected in the tonsils of latently infected calves. Detection of the latency-related transcript (LRT) in tonsils of latently infected calves required nested reverse transcription-PCR (RT-PCR) suggesting that only a few cells contained viral DNA or that LRT is not an abundant transcript. bICP0 (immediate-early and early transcripts), ribonucleotide reductase (early transcript), and glycoprotein C (late transcript) were not detected by RT-PCR in latently infected calves. When reactivation was initiated by dexamethasone, bICP0 and ribonucleotide reductase transcripts were detected. Following dexamethasone treatment, viral nucleic acid was detected simultaneously in trigeminal ganglionic neurons and lymphoid follicles of tonsil. LRT was detected at 6 and 24 h after dexamethasone treatment but not at 48 h. Dexamethasone-induced reactivation led to apoptosis that was localized to tonsillar lymphoid follicles. Taken together, these findings suggest that the tonsil is a site for persistence or latency from which virus can be reactivated by dexamethasone. We further hypothesize that the shedding of virus from the tonsil during reactivation plays a role in virus transmission.

Persistence of herpes simplex virus type 1 DNA in chronic conjunctival and eyelid lesions of mice

Herpes simplex virus type 1 (HSV-1) causes chronic blepharitis and conjunctivitis as well as keratitis in humans. The pathogenesis of these inflammatory ocular and dermal lesions is not well understood. We have examined the persistence of HSV-1 DNA and its relationship to inflammatory lesions in the conjunctiva and eyelid skin of mice which were inoculated with HSV-1 by the corneal route. Viral DNA was detected by in situ PCR in the conjunctiva and eyelid tissue of infected mice at 5, 11, 23, and 37 days postinfection (p.i.). This DNA was localized in the epithelial cells of the conjunctiva and hair follicles and in the epidermal cells of the eyelid skin. Viral proteins were not detected in the conjunctiva or the eyelid skin after 5 days p.i., even though histopathological lesions were found at 23 and 37 days p.i. in both tissues. The DNA-containing cells were adjacent to sites of inflammation in the chronic lesions in both the conjunctiva and the eyelid skin. A similar temporal and spatial relationship between HSV-1 DNA and inflammatory lesions has been previously reported for the cornea. Our data suggest that the lesions in the cornea, conjunctiva, and eyelid skin progress similarly. Further studies are required to determine whether the long-term presence of HSV-1 is involved in the mechanism by which these chronic inflammatory lesions develop. The presence of HSV-1 DNA in these extraocular tissues for extended periods may constitute persistent viral infection of nonneuronal cells.

Examination of non-involved skin, previously involved skin, and peripheral blood for herpes simplex virus DNA in patients with recurrent herpes-associated erythema multiforme

The association between infection with HSV and the subsequent development of erythema multiforme is well established, although the role that the virus plays in the pathogenesis of this disorder is not known. HSV DNA has been detected in cutaneous lesions of herpes-associated erythema multiforme (HAEM), and it has been suggested that the tissue damage seen in these lesions is virus-specific. In the current, prospective study, we examined biopsies of lesional, non-involved, and previously involved but healed skin, in addition to specimens of peripheral blood, from patients with HAEM, for HSV DNA by using the polymerase chain reaction. HSV DNA was detected in lesional skin of 10 of 11 patients compared to 2 of 11 non-involved skin biopsies obtained at the same time. HSV was present in 4 of 6 blood specimens obtained during the acute episode. Five patients returned 3 months after the acute episode resolved for biopsies of previously involved skin. HSV was detected in 4 of these 5 biopsies. Thus, the presence of HSV DNA in the skin of patients with HAEM appears to be predominantly in areas of clinical involvement; the virus remains in those cutaneous sites for up to 3 months without evidence of clinical disease; and HSV DNA may be detected in the peripheral blood cells during acute HAEM. Based on these findings, we suggest that the virus plays a role in lesion development, that the skin may function as a site of viral persistence, and that hematogenous spread of viral DNA may be an important factor in the development of HAEM.

Detection of herpes simplex virus in gingival tissue

The presence of herpes simplex virus (HSV) antigens was shown by immunofluorescence staining in 26 of 66 (39.3%) specimens of clinically healthy gingiva, but only one sample contained infectious virus. HSV DNA sequences were clearly identified in intact gingival cells by dot blot hybridization in one specimen, and a weak pattern in a second one. Both specimens harbored viral antigens. These findings of viral genome and protein expression suggest that the virus is present in the latent form in the gingiva.

Localization of herpes simplex virus type 1 in sebaceous glands of mice

The distribution of HSV-1 during the development of zosteriform skin lesions in SCID mice was analyzed by immunofluorescence and electron microscopy. The virus initially appeared within certain keratinocytes, sometimes surrounded by keratinocytes whose surfaces were also positive for the antigens, in the lower epidermal layers including the hair follicles, and then extended upward to the entire epidermis and downward to the sebaceous glands 1-2 days later, when no macroscopic skin lesion was seen. The affected epidermal cells subsequently degenerated and lost their viral antigens within a day, when the zosteriform lesion then became evident. This was followed by a degeneration of the dermis. The sebaceous glands eventually degenerated in 10 days, but some glands in the necrotic skin areas preferentially retained HSV-1. The horizontal spread of the virus in the epidermis beyond the first invaded dermatome occurred much later. In mice passively immunized with specific immune serum, viral antigens were observed even 20 days after the infection in sebaceous glands in necrotized areas. Therefore, HSV-1 appears to spread first via the extracellular fluid among the keratinocytes after being shed from nerve endings, and then produces a successive degeneration of the affected keratinocytes which may prevent any further extension of horizontal viral spread. The pilosebaceous apparatus is possibly acting as a site not only for the replication of HSV-1 with a delayed cytopathic effect, but also as an area that is temporarily sheltered from host defense mechanisms.

Detection of viral DNA within skin of healed recurrent herpes simplex infection and erythema multiforme lesions

The polymerase chain reaction (PCR) was used to detect HSV DNA in genomic DNA extracted from skin biopsies obtained from healed skin of five patients with hyperpigmented macules following recurrent cutaneous HSV infections and from eight patients with HSV-associated erythema multiforme (EM). A 92-bp HSV-1 DNA fragment was found in all the skin biopsies from the site of recurrent HSV infection and in five of eight (62%) biopsies from the EM patients. Virus DNA was not found in tissues distant from the site of HSV recurrence or from a patient without a history of HSV infection. These findings confirm the presence of HSV in healed skin from the site of recurrent HSV disease and are consistent with the concept that HSV is involved in EM pathogenesis.

Herpes simplex virus: molecular biology and the possibility of corneal latency

Herpes simplex virus (HSV) is known to be latent in ganglionic neurons. Over the past eight years, a series of reports have described the isolation of HSV after organ culture of human corneas that had been removed in the course of penetrating keratoplasty. None of the corneas showed any clinical signs of active herpetic disease immediately before keratoplasty. Studies in rabbits and mice confirmed that HSV can be recovered from corneas by organ culture long after primary infection has subsided. Recently, sophisticated techniques of molecular biology, such as specific DNA or RNA probes, have been used to detect HSV nucleic acids in the cornea. The crux of the matter is whether the virus recovered from or detected in the cornea is 1) truly latent in cell populations that are nonneuronal; 2) resident in the cornea, replicating at a slow rate; or 3) newly arrived in the cornea following ganglionic reactivation. The evidence suggests that a guarded case can be made for limited HSV latency within corneal cells. HSV corneal latency would allow for reactivation, replication, and the immune response to occur in the absence of ganglionic HSV reactivation. Such a localized phenomenon has not, however, been demonstrated to occur clinically.

Characterization of herpes simplex virus type 2 transcription during latent infection of mouse trigeminal ganglia

Using a cornea trigeminal ganglion model, we have investigated transcription by herpes simplex virus type 2 (HSV-2) during latency in mice. Latency was verified 2 months postinoculation by reactivation of HSV-2 after explant cocultivation of trigeminal ganglia from the majority of mice (83%). Transcription during latent HSV-2 infection was limited to the repeat regions of the viral genome as determined by in situ hybridization using restriction fragment probes representing 100% of the HSV-2 genome. Further mapping of the positively hybridizing region by using subfragments showed that transcription occurred from approximately 11.5 kb of contiguous DNA fragments. A 1.0-kb PvuI-BamHI fragment within the BamHI F fragment and a 0.3-kb BamHI-SalI fragment and a 3.4-kb SalI-BamHI fragment within the BamHI P fragment hybridized more strongly than other subfragments in in situ hybridization experiments. All positive signals were confined to the nucleus. The RNA that hybridized to the 3.4-kb SalI-BamHI DNA fragment probe by in situ hybridization corresponded to a 2.3-kb transcript on Northern (RNA) blots. Under our conditions for Northern blot hybridization, the 3.4-kb SalI-BamHI probe of HSV-2 hybridized to a limited degree with the latency-associated transcripts of HSV-1. Shorter spliced species of latency-associated transcript RNA, which are seen during HSV-1 latency, have not been detected in latent HSV-2 RNA. However, viral gene expression during HSV-2 latency appears to be very similar to that during HSV-1 latency.

Reactivation of latent herpes simplex virus-1 (HSV) from mouse footpad cells demonstrated by in situ hybridization

HSV-1 specific RNA sequences became detectable by in situ hybridization 5-6 days after culture of footpads (FP) explanted from latently infected mice. HSV-specific RNA first appeared in basal cells of hair follicles and cells of the hair root sheath, in epithelial cells of sebaceous glands and in cells within the epidermis. When first detected graining was light and usually present over individual cells, subsequently graining became heavy and present over large groups of cells. HSV reactivation from latency could be demonstrated in individual cells and therefore identified those cells in which the virus has been latent. The heavy graining over clumps of cells characteristic of a lytic infection was seen at later times after explantation; we infer that the infection had spread progressively from the initial foci of reactivation from latency.

Detection of HSV nucleic acid sequences in the cornea during acute and latent ocular disease

This study evaluated the continued presence of herpes simplex virus (HSV) nucleic acid sequences after resolution of acute herpetic stromal keratitis in the rabbit ocular model. Forty-four rabbits were inoculated bilaterally with 10(5) plaque-forming units of RE strain HSV-1 by intrastromal injection. All eyes were cultured for the presence of HSV during acute disease and immediately before the animals were killed. Full-thickness corneal buttons were then removed and processed for in situ hybridization with a 3H-labelled HSV DNA probe representing the full-length HSV genome. HSV nucleic acid sequences were detected autoradiographically at all time intervals examined. HSV nucleic acid sequences were localized in the epithelium and the anterior stromal keratocytes during acute disease and in all corneal layers during latent infection. Retention of HSV nucleic acid sequences, either HSV DNA or HSV RNA, or both, in corneal tissues (epithelium, stroma, and endothelium) may be a contributing factor in the development of HSV-induced stromal keratitis.

Chronic herpes simplex virus and varicella zoster virus infection

After defining such terms as persistent and chronic infection, latency, recurrence, recrudescence, and exogenous reinfection they are applied to infections with HSV and VZV. Possible factors determining pathogenicity are discussed, and an overview is given of the wide range of illnesses and case reports ascribed to HSV and VZV infections. Various types of infection afford different diagnostic procedures. Besides virus isolation supplemented by viral antigen identification IgG antibody tests (increase in titer) may be useful. IgG subtype and IgA antibody determinations appear to be of limited value. Despite the rather large number of available tests, there are still considerable shortcomings in their ultimate significance as to the patient's disease. Thus, some new experimental approaches are mentioned.

Enhanced in vitro reactivation of latent herpes simplex virus from neural and peripheral tissues with hexamethylenebisacetamide

We evaluated the effect of the demethylating agent hexamethylenebisacetamide on reactivation of latent herpes simplex virus type 2 (HSV-2) from guinea pig neural and extraneural tissues. Four explant cultures from the dorsal root ganglia of 42 latently infected guinea pigs and vaginal and cervical explant cultures from 33 animals were divided so that half received 5 mM of hexamethylenebisacetamide supplemented media and half media alone. HSV-2 was recovered earlier and from a greater percentage of treated cultures than controls. For example, seven days after explant, HSV-2 was recovered from 35 of 84 (42%) treated dorsal root ganglia cultures compared to seven of 84 control cultures (p less than 0.0001). Likewise, HSV-2 was recovered seven days after explant from 11 of 66 (17%) treated external genital skin cultures and 2 of 66 control cultures (p less than 0.009), Hexamethylenebisacetamide had no effect on productive HSV-2 infection in guinea pig dorsal root ganglia cultures. This study provides evidence for a role of demethylation in the reactivation of latent HSV from neural as well as peripheral tissues and suggests that latent virus exists at these sites in a similar state. Hexamethylenebisacetamide should be useful in studies of herpes virus latency because it decreases the time necessary to recover virus from latently infected tissues and enhances the recovery of virus.

An animal model of type-1 herpes simplex virus infection of facial nerve

As the pathogenesis of Bell's palsy, herpes simplex virus (HSV) infection has been suggested on the basis of several serological studies. To clarify and analyse the pathogenic mechanisms of this disease, guinea pigs were inoculated with type-1 HSV through natural infection routes into the peripheral areas innervated by facial nerve, and nervous tissues were examined by histopathological and immunohistochemical methods. HSV-I infection in the nasal mucosa, tongue, oral muscles and auricles brought about neither clinical facial palsy nor disturbed Preyer or corneal reflexes, but viral antigens in the inoculated peripheral areas, facial and trigeminal ganglia and pons with inflammatory cell response, hemorrhages and degeneration and necrosis. Cyclophosphamide treatment resulted in disturbed Preyer and corneal reflexes and enhanced the incidence of antigen appearance and histopathological changes.

The quest for a herpes simplex virus vaccine: background and recent developments

Herpes simplex virus infections in humans range from localized skin infections of the oral, ocular and genital regions, to severe and often fatal disseminated infections of immunocompromised hosts. Following primary infection, the virus often becomes established in a latent form in the neurons of sensory ganglia and can reactivate to excrete virus asymptomatically or produce recrudescent lesions. This review describes some of the mechanisms involved in the immune response against HSV infections and examines the different strategies adopted to develop a vaccine against this seemingly intractable disease.

Amplification of herpes simplex virus resistance in mouse neuroblastoma (Cl300) cells

Clones of mouse neuroblastoma (Cl300) cells with increased resistance to herpes simplex virus (HSV) were obtained among survivors after prolonged exposure of partially HSV resistent Cl300 cells to successively increasing multiplicities of infection (MOI) of HSV. The increased restrictedness to HSV of these Cl300 R clones (Cl300 RI and Cl300 RII) as compared to the parental Cl300 cells was demonstrated by a tolerance to higher MOIs of HSV, judged by the appearance of cytopathic effects; by lower yields of progeny virus; and by higher activities of a non-interferon HSV inhibitor. Morphological appearance, cellular growth rate as well as HSV adsorptive capacity of the Cl300 R cells did not differ from that of Cl300 cells. Neither was virus penetration affected. These neuroblastoma Cl300 R cells, demonstrating an amplified resistance to HSV, might serve useful in studies on the regulation of virus replication in HSV latency establishment in neurons.

Thymidine kinase-deficient herpes simplex virus type 2 genital infection in guinea pigs

In guinea pigs, thymidine kinase-producing strains of herpes simplex virus type 2 replicated to high titer in the vagina and spinal cord, and animals developed severe clinical disease. Infection with thymidine kinase-deficient virus resulted in similar vaginal virus titers; however, animals exhibited little or no clinical illness and only low titers of virus were detected in spinal cord homogenate cultures. Neural and extraneural latent infection as well as recurrent infection were noted in animals inoculated with either thymidine kinase-producing or -deficient viruses. These data suggest that neural pathways are important in the pathogenesis of genital herpes and that virus-coded thymidine kinase may influence virulence but is not required for latency.

Herpes simplex virus type 2 establishes latency in the mouse footpad and in the sensory ganglia

Three mouse strains as well as wt and 7 ts mutants of herpes simplex virus (HSV) type 2 (strain HG52) have been used to investigate latency. The mice were inoculated in the right rear footpad. Virus reactivation following explanation and culture of the dorsal root ganglia and the footpad was scored. The results show that: HSV-2 can be maintained in the mouse footpad in a state indistinguishable from latency; virus gene functions necessary for latency can be identified by the use of ts mutants; and mouse strains differ in their ability to support latent infection. An infectious center assay was used to quantitate virus reactivation from dissociated dorsal root ganglia. HSV-1 strain 17 wt spread after inoculation at doses of greater than or equal to 5.0 X 10(5) plaque-forming units (pfu), producing latency also in contralateral ganglia but with lower efficiency.

The DNA of an IPV strain of bovid herpesvirus 1 in sacral ganglia during latency after intravaginal infection

Two calves were inoculated intravaginally with a strain of bovid herpesvirus type 1 (BHV-1, IBR/IPV) isolated from a cow with infectious pustular vulvovaginitis (IPV). The animals were killed during a latent stage of infection as characterized by seroconversion, absence of virus shedding and recrudescence of virus shedding after dexamethasone treatment. IPV-virus DNA was detected in 9 out of 20 sacral ganglia of the 2 calves. Of the sections, 7.2% (n = 250) contained 1 cell with IPV-virus DNA, which was restricted to the nucleus of neurons. In agreement with findings on herpes simplex virus infections, the viral DNA of BHV-1 is harbored in the local sensory ganglia. Virological and serological implications of the latent IPV infection are discussed.

Sensitivity of oral tissues to herpes simplex virus--in vitro

Epithelial and fibroblast cells from the human gingival sulcus area were cultivated in vitro, and their sensitivity to the herpes simplex virus (HSV) was studied. Fibroblasts were sensitive to HSV infection and supported virus multiplication as evidenced by nuclear inclusion bodies and a cytopathogenic effect. Epithelial cells which were primarily devoid of HSV antigens were infected with HSV as demonstrated by positive immunofluorescent staining and damage to the cells at a later stage. Epithelial cells that were found to harbor HSV antigens upon removal from the patients prior to infection in vitro, maintained these antigens throughout the period of in vitro cultivation. The sensitivity of both epithelial cells and fibroblasts from the gingival sulcus area to HSV infection in vitro is significant for the understanding of the role of these tissues as a primary site of infection and as a possible reservoir for the latent virus between recurrences.

Detection of herpes simplex virus mRNA in latently infected trigeminal ganglion neurons by in situ hybridization

Latent infection of the trigeminal ganglion with herpes simplex virus type 2 (HSV-2) was studied in guinea pigs by in situ DNA hybridization. Frozen ganglion sections from animals killed during the period of latent virus infection were studied under nondenaturing conditions. Some sections were treated with deoxyribonuclease (DNase) or ribonuclease (RNase) before incubation with HSV DNA probes. HSV probes consisted of viral DNA nick translated and labeled in vitro with tritiated nucleotides. Bacteriophage lambda DNA, similarly prepared, was used as a control probe. The lambda probe was negative in all situations, including HSV-2-infected monolayer cells in cell culture. HSV-2 probes produced heavy label and, therefore, evidence of hybridization with HSV-2-infected monolayer cells. When HSV-2 probes were incubated with latently infected ganglion sections, hybridization was detected in 71% of guinea pigs and 46% of ganglia. Label was seen only in neurons, and in positive ganglia 0.3 to 5% of neurons were labeled. The amount of label was markedly decreased by pretreatment of ganglion sections with RNase but not DNase, indicating that the DNA probes hybridized to HSV messenger RNA in the latently infected ganglia.

Pathogenesis of Herpes simplex virus infections in guinea pigs

The pathogenesis of herpes simplex virus types 1 and 2 has been studied in guinea pigs after inoculation by various routes (subcutaneous and intradermal infection in footpads and vaginal infection). Clinical observations as well as virus isolation studies are reported. Herpes simplex virus type 2 infection by all three routes of inoculation led to acute primary and recurrent lesions. Virus persisted in the nervous system, particularly in sensory ganglia, and locally at the site of inoculation. Herpes simplex virus type 1 infection induced no or very mild primary symptoms. Recurrent lesions were only observed after intradermal inoculation. Invasion of the nervous system and consequent establishment of latent ganglionic infection was less efficient than after herpes simplex virus type 2 infection. Peripheral persistence was, however, equally common.

Persistence of herpes simplex virus (HSV) infection in ganglia and peripheral tissues of guinea pigs

HSV infections in guinea pigs are shown to persist independently in dorsal root ganglia and skin at the site of initial inoculation. The same may also hold for ganglia and vagina after genital infections. Evidence is presented that the state of persistent virus might be different in ganglia and peripheral tissue.

Pathogenicity of wild-type and temperature-sensitive mutants of herpes simplex virus type 2 in guinea pigs

The pathogenicity of herpes simplex virus type 2 strain 186, the wild-type (WT) strain, and four temperature-sensitive (ts) mutants was studied after genital inoculation of female guinea pigs. Infection with the WT virus was generally severe, with extensive skin lesions in 89% and mortality in 37% of inoculated animals. Guinea pigs inoculated with ts mutants manifest remarkably mild disease, with lesions occurring in only 16% of the guinea pits and a mortality rate of 7%. WT virus was recovered from nerve and non-nerve tissues of all acutely infected animals and from the majority of latently infected animals (71%). Virus was isolated from nerve or genital tissues from only 13% of ts mutant-inoculated animals during acute infection and from 7% during latent infection. Three of the seven isolates from mutant-infected animals appeared to be WT virus. Identification of WT and ts mutant isolates was done by biological characterization in selective cell cultures at permissive (33 degrees C) and nonpermissive (38 degrees C) temperatures. One month after initial infection with WT virus, guinea pigs were challenged with the same virus and were completely resistant to overt clinical disease. Animals inoculated with ts mutants A1b and C2b had mild manifestations of disease after challenge with WT virus; however, the capacity of WT virus to establish latent infection was conserved. Although complement-required neutralizing antibodies were detectable after challenge in animals previously inoculated with mutant virus A1b, C2b, or D6b, there was no significant protection against subsequent infection with WT virus. No complement-required neutralizing antibodies were detected in F3b animals after challenge. The present study of WT and ts mutants of herpes simplex virus type 2 in the guinea pig model provides a means for better understanding the mechanisms of pathogenesis and latency after genital infection.

Immunity to herpes simplex virus type 2: cell-mediated immunity in latently infected guinea pigs

Cell-mediated (CMI) and humoral immunity to herpes simplex virus type 2 (HSV-2) were evaluated in infected strain 13/N guinea pigs with (45%) and without a history of recurrent herpetic disease. Virus was isolated by cocultivation from active herpetic lesions (9 of 10) as well as from the footpads (17 of 38), sacral ganglia (7 of 21), and sciatic nerves (1 of 21) of asymptomatic animals. Viral isolates grew in cells of human origin and were neutralized by hyperimmune anti HSV-2 sera. Humoral immunity measured by the presence of virus-neutralizing antibody was similar in both experimental groups. The involvement of CMI in recurrent disease was assessed by comparing lymphocyte transformation (LT) and leukocyte migration inhibition factor (LIF) responses in animals with a history of recurrent disease studied while asymptomatic (quiescent) and in animals without clinical evidence of recurrent disease (seropositive controls). Spleen cells from quiescent animals evidenced significant impairment of both LIF and LT responses as reflected in the requirement of higher antigen concentrations (up to 58-fold) and longer in vitro culture periods (up to 2.5 days) to mount responses comparable in magnitude to those observed in the seropositive control groups. Peripheral blood lymphocyte cultures obtained from quiescent animals showed similar impairment of LIF responses but displayed intact LT response. The data suggest that recurrent disease is associated with an impairment in the generation of anamnestic effector functions as reflected by altered kinetics and dose response patterns in in vitro secondary responses.

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.

Use of [125I]deoxycytidine to detect herpes simplex virus-specific thymidine kinase in tissues of latently infected guinea pigs

The footpad skin and the lumbosacral dorsal root ganglia were removed from inbred guinea pigs at different times after subcutaneous infection with herpes simplex virus type 2 (HSV-2) in both hind footpads. These tissues, shown by our previous study to harbor latent HSV, were dispersed into single cells. The presence of virus-specific thymidine kinase (TK) in these cells was assayed by the uptake and phosphorylation of [125I]deoxycytidine in culture. [125I]deoxycytidine was shown to be a specific substrate for the HSV-coded TK. The method could detect herpes TK activity in a culture of 10(6) cells with less than 0.1% of the cells being virally infected. The enzyme was readily detected in footpad cells of acutely (24 h) but not of latently (14 days to 1 year) infected guinea pigs. No herpes TK was found either in the sensory ganglionic cells of guinea pigs during the early and late phases of latent infection. It is concluded that HSV-2, while residing in the footpads and the lumbosacral ganglia of the guinea pig during latent infection, does not express any viral TK function.

Surgical conversion of herpes simplex from an epidermal to a dermal disease

A new post-surgical form of recurrent herpes simplex is described. It appeared as an erythematous bulla at sites of recurrent herpes from which the prior epidermal lesion had been transversely excised. Histologically, it was characterized by a lesion-free epidermis, a large subepidermal bulla, and a marked inflammatory response in the uppermost dermis, complete with diagnostic multinucleate giant cells. It is postulated that epidermal surgery leaves the area immune to future direct herpetic involvement of the epidermis because it denervates the epidermis. The possibility is raised that such dermal forms of herpes may also occur in the natural course of the disease.

Protection of guinea pigs against primary and recurrent genital herpes infections by immunization with live heterologous or homologous Herpes simplex virus: implications for a herpes virus vaccine

Guinea pigs, inoculated intravaginally with HSV type 2 develop a primary and spontaneously recurring genital herpes with clinical symptoms resembling genital herpes in humans. The effect of a previous infection with either HSV type 1 or HSV type 2 on the clinical course of the intravaginal challenge infection was studied. Prior infection with either subtype of HSV moderated considerably the acute disease induced by intravaginal HSV type 2 challenge. No effect was, however, observed on the development of the chronic phase of the challenge infection. The significance of these studies for the possibility of vaccination against recurrent herpes infections is discussed.

Persistence in herpes simplex virus infections

Diseases of man caused by the virus of herpes simplex fall into two broad categories. The primary disease occurs only once in any individual's life and is caused by transmission of virus from an already infected human. Thereafter, the individual may be subject to recurrent herpetic disease, the manifestations of which are different from the primary disease. Recurrent disease varies in severity from trivial, to incapacitating and frankly lethal (as in diseases resulting from the virus's neurotropic and oncogenic properties). The source of the virus in recurrent herpetic disease has never been conclusively resolved, but is almost certainly endogenous to the patient. Theories, case reports and experiments exist to show that endogenous virus may, in periods of clinical quiescence, be latent (or persistent) at the site of the recurrent lesions itself, or more remotely in nerve tissues related to the site of recurrence.