Virological and molecular biological evidence supporting herpes simplex virus type 1 corneal latency

Occurrence of Herpes Viruses in Morphologically Normal Corneas

PURPOSE

The purpose of this study was to detect the occurrence of herpes simplex virus (HSV) types 1 and 2 and varicella zoster virus (VZV) DNA in transplanted corneas using polymerase chain reaction (PCR) and to determine the relationship between latent HSV and VZV and herpetic eye disease in recipients.

METHODS

This was a retrospective, interventional case series. Samples from 88 donor corneoscleral buttons (CSBs) were collected from the conjunctiva, iris, and endothelium and tested for HSV-1, HSV-2, and VZV DNA using PCR. All transplanted eyes were evaluated and followed up. The main outcome measures were HSV-1, HSV-2, and VZV DNA positivity rates in donor CSBs and the occurrence of herpetic eye disease or graft failure in recipients of positive corneas.

RESULTS

HSV-1 DNA was detected in 5 (5.7%) of 88 CSBs. HSV-2 was not detected in any CSBs, and VZV was found in 1 (1.2%) of the 82 examined CSBs. One recipient (16.7%) developed dendritic epitheliopathy and keratouveitis typical of HSV 12 months after transplantation, although the graft remained clear after treatment. One cornea was used for a tectonic graft and stayed edematous at the 20-month follow-up. The remaining corneas remained clear.

CONCLUSIONS

Morphologically normal donor corneas may be PCR-positive for herpes viruses, especially HSV-1. Recipients of herpes-positive corneal grafts could be at risk for herpetic eye disease. Further studies using viral RNA by reverse transcriptase PCR are needed to provide more information on HSV and VZV latency and active replication in donor corneas.

Role of Heparanase and Syndecan-1 in HSV-1 Release from Infected Cells

Herpes Simplex Virus 1 (HSV-1) is a neurotropic human virus that belongs to the Alphaherpesvirinae subfamily of Herpesviridae. Establishment of its productive infection and progression of disease pathologies depend largely on successful release of virions from the virus-producing cells. HSV-1 is known to exploit many host factors for its release. Recent studies have shown that heparanase (HPSE) is one such host enzyme that is recruited for this purpose. It is an endoglycosidase that cleaves heparan sulfate (HS) from the surface of infected cells. HS is a virus attachment coreceptor that is commonly found on cell surfaces as HS proteoglycans e.g., syndecan-1 (SDC-1). The current model suggests that HSV-1 during the late stage of infection upregulates HPSE, which in turn enhances viral release by removing the virus-trapping HS moieties. In addition to its role in directly enabling viral release, HPSE accelerates the shedding of HS-containing ectodomains of SDC-1, which enhances HSV-1 release via a similar mechanism by upregulating CREB3 and COPII proteins. This review outlines the role of HPSE and SDC-1 as newly assigned host factors that facilitate HSV-1 release during a lytic infection cycle.

Absence of Herpesvirus DNA in Aqueous Humor from Asymptomatic Subjects

Purpose

To assess herpesvirus DNA detection in aqueous humor from a cohort of asymptomatic Scandinavian patients undergoing elective cataract surgery.

Patients and Methods

Prospective case series. Aqueous samples were obtained from 30 patients undergoing elective cataract surgery. Polymerase chain reaction (PCR) analysis for herpes simplex virus 1 (HSV1), herpes simplex virus 2 (HSV2), cytomegalovirus (CMV), Epstein Barr virus (EBV) was performed. Toxoplasma was added to the analysis due to its role as pathogen with ocular latency.

Results

Mean age of participants was 75.3 years. Sixteen subjects (53%) had ocular comorbidities. Five subjects (17%) had endothelial dysfunction without known hereditary pattern. None of the samples were positive for herpesviruses or toxoplasma.

Conclusion

None of the aqueous samples were positive, suggesting shedding does not frequently occur in the aqueous humor of asymptomatic patients.

Herpes simplex virus PCR in 2230 explanted corneal buttons

PURPOSE

To determine herpes simplex virus (HSV) DNA prevalence and mean cycle threshold of polymerase chain reaction (PCR) in corneal tissue of patients with penetrating keratoplasty (PKP), with (HSK+) and without (HSK-) previous clinical herpetic keratitis history.

METHODS

Retrospective review of recipient corneal buttons which were explanted through PKP between March 2010 and September 2018 at the Department of Ophthalmology, Saarland University Medical Center in Homburg/Saar, Germany. Corneal tissue samples were analysed by real-time PCR for the presence of HSV DNA. For each subject, clinical data, including patients' demographics and clinical diagnoses, were collected.

RESULTS

In total, 2230 corneal samples (age at the time of the surgery 57.3 ± 19.2 years) of 1860 patients were analysed. HSV PCR was positive in 137 (6.1%) corneal samples, with a 30.57 ± 6.01 (range 14-39) mean cycle threshold (Ct) value. Two hundred ninety-eight (13.4%) corneas of 266 patients were clinically HSK+, and 1932 (86.6%) corneas of 1600 patients were clinically HSK-. HSV DNA was detected significantly more frequently (p < 0.0001) in HSK+ corneal samples (108 corneal samples; 36.2%), than in HSK- corneal samples (29 corneal samples; 1.5%). Ct value was significantly lower in HSK+ than in HSK- corneal samples (29.8 ± 5.8 versus 32.6 ± 5.9; p = 0.008).

CONCLUSION

Our data demonstrate that a positive clinical history of HSK is related to HSV PCR positivity in about every 2.8th patient. In addition, about every 66th explanted corneal tissue is HSV PCR-positive despite the lack of clinical suspicion. These patients may need additional local/systemic antiviral treatment to avoid newly acquired HSK following penetrating keratoplasty.

Quantitative analysis of herpes simplex virus-1 transcript in suspected viral keratitis corneal buttons and its clinical significance

Purpose:

The evaluation of Herpes Simplex virus-1 (HSV-1) transcript by different investigative methods (qPCR, PCR and IHC) in corneal buttons from suspected viral keratitis patients and the comparison of results with histopathological findings and clinical diagnosis.

Methods:

Sixty corneal buttons, 30 suspected viral keratitis, and 30 controls (keratoconus and bullous keratopathy) obtained after primary penetrating keratoplasty, were included in the study. All the corneal buttons were subjected to reverse transcriptase quantitative PCR (qPCR) for the detection of latency-associated transcript (LAT) gene, conventional PCR for polymerase (pol) gene, and immunohistochemistry (IHC) for HSV-1 antigen respectively. After obtaining baseline preoperative clinical data, all the patients were followed up for three years. The results obtained were correlated with clinicopathological features and follow-up data.

Results:

Of the 30 suspected viral keratitis patients there were 6 females and 24 males with mean age 46.5 ± 24.62 years (3-80 yrs). There was a marked male preponderance (80%). HSV-1 LAT transcript was detected in 23% (7/30) corneal buttons by qPCR, HSV-1 DNA in 6.7% (2/30) and HSV-1 antigen in 30% (9/30) cases by conventional PCR and IHC respectively. A statistically significant association was found between qPCR and DNA PCR (P = 0.04). All the 30 control corneas were negative for HSV-1 LAT gene, DNA and antigen.

Conclusion:

Detection of HSV-1 LAT transcript by qPCR may be superior to HSV-1 DNA PCR (conventional) and IHC, which has low sensitivity. However, the utility of HSV-1 LAT mRNA analysis as a diagnostic modality by qPCR needs to be validated on a larger patient cohort.

Disturbed Yin-Yang balance: stress increases the susceptibility to primary and recurrent infections of herpes simplex virus type 1

Herpes simplex virus type 1 (HSV-1), a neurotropic herpes virus, is able to establish a lifelong latent infection in the human host. Following primary replication in mucosal epithelial cells, the virus can enter sensory neurons innervating peripheral tissues via nerve termini. The viral genome is then transported to the nucleus where it can be maintained without producing infectious progeny, and thus latency is established in the cell. Yin–Yang balance is an essential concept in traditional Chinese medicine (TCM) theory. Yin represents stable and inhibitory factors, and Yang represents the active and aggressive factors. When the organism is exposed to stress, especially psychological stress caused by emotional stimulation, the Yin–Yang balance is disturbed and the virus can re-engage in productive replication, resulting in recurrent diseases. Therefore, a better understanding of the stress-induced susceptibility to HSV-1 primary infection and reactivation is needed and will provide helpful insights into the effective control and treatment of HSV-1. Here we reviewed the recent advances in the studies of HSV-1 susceptibility, latency and reactivation. We included mechanisms involved in primary infection and the regulation of latency and described how stress-induced changes increase the susceptibility to primary and recurrent infections.

Evaluation of multiplex real-time polymerase chain reaction for the detection of herpes simplex virus-1 and 2 and varicella-zoster virus in corneal cells from normal subjects and patients with keratitis in India

Purpose

To determine the presence of herpes simplex virus and varicella zoster virus (HSV 1 and 2, VZV) in the cornea of normal subjects by multiplex real time quantitative (qPCR) assay and evaluate its utility in the diagnosis of viral keratitis.

Methods

Corneal epithelial cells from 33 eyes of 22 patients undergoing photorefractive keratectomy surgery (controls) and 50 corneal scrapings from 50 patients with suspected HSV keratitis were analyzed for the presence of HSV1 by conventional PCR and for presence of HSV1 and 2 and/or VZV by multiplex real-time PCR. Corneal scrapings of patients were also tested for HSV1 antigen by immunofluorescence assay (IFA). The results were compared and clinical records reviewed.

Results

HSV1 and VZV DNA were detected in 8/33 controls (mean-14.3 ± 7.96, range: 3-29.1 copies/mL) and 2/33 controls (mean-10.7 ± 10.9, range 3-18.5 copies/ml) respectively. HSV2 was not detected in any of the controls. Copy numbers above the mean + 1SD of controls were considered significant for viral load in patient samples. Significantly higher number of corneal scrapings (39/50, 78%) from patients were positive for HSV1 (1.2 × 10⁶ copies/mL ± 3.7 × 10⁶ copies/mL) by real time qPCR compared to IFA (11/48, 23%, P value 0.0001) and conventional PCR (20/50, 40%, P value 0.0002). Double infection with HSV-1 (1.5 × 10⁷ copies/ml) and HSV-2 (3.57 × 10⁴ copies/ml) in one case and VZV infection (1.03 × 10² copies/ml) in another was also detected by the multiplex real-time PCR.

Conclusion

Multiplex real-time PCR reliably detects HSV1 and 2 and VZV DNA and is ideal for the diagnosis of HSV and VZV keratitis in an ocular microbiology laboratory.

Pathogenesis of herpes simplex keratitis: The host cell response and ocular surface sequelae to infection and inflammation

Herpes simplex virus type 1 (HSV) keratitis is a leading cause of infectious blindness. Clinical disease occurs variably throughout the cornea from epithelium to endothelium and recurrent HSV stromal keratitis is associated with corneal scarring and neovascularization. HSV keratitis can be associated with ocular pain and subsequent neutrophic keratopathy. Host cell interactions with HSV trigger an inflammatory cascade responsible not only for clearance of virus but also for progressive corneal opacification due to inflammatory cell infiltrate, angiogenesis, and corneal nerve loss. Current antiviral therapies target viral replication to decrease disease duration, severity and recurrence, but there are limitations to these agents. Therapies directed towards viral entry into cells, protein synthesis, inflammatory cytokines and vascular endothelial growth factor pathways in animal models represent promising new approaches to the treatment of recurrent HSV keratitis.

Herpes Simplex Virus Establishment, Maintenance, and Reactivation: In Vitro Modeling of Latency

All herpes viruses establish lifelong infections (latency) in their host, and herpes simplex viruses (HSVs) are highly prevalent worldwide. Recurrence of HSV infections contributes to significant disease burden in people and on rare occasion can be fatal. Cell culture models that recapitulate latent infection provide valuable insight on the host processes regulating viral establishment and maintenance of latency. More robust and rapid than infections in live animal studies, advancements in neuronal culture techniques have made the systematic analysis of viral reactivation mechanisms feasible. Only recently have human neuronal cell lines been available, but models in the natural host cell are a critical addition to the currently available models.