The comparative effects of famciclovir and valacyclovir on herpes simplex virus type 1 infection, latency, and reactivation in mice

A Human Stem Cell-Derived Neurosensory–Epithelial Circuitry on a Chip to Model Herpes Simplex Virus Reactivation

Both emerging viruses and well-known viral pathogens endowed with neurotropism can either directly impair neuronal functions or induce physio-pathological changes by diffusing from the periphery through neurosensory–epithelial connections. However, developing a reliable and reproducible in vitro system modeling the connectivity between the different human sensory neurons and peripheral tissues is still a challenge and precludes the deepest comprehension of viral latency and reactivation at the cellular and molecular levels. This study shows a stable topographic neurosensory–epithelial connection on a chip using human stem cell-derived dorsal root ganglia (DRG) organoids. Bulk and single-cell transcriptomics showed that different combinations of key receptors for herpes simplex virus 1 (HSV-1) are expressed by each sensory neuronal cell type. This neuronal–epithelial circuitry enabled a detailed analysis of HSV infectivity, faithfully modeling its dynamics and cell type specificity. The reconstitution of an organized connectivity between human sensory neurons and keratinocytes into microfluidic chips provides a powerful in vitro platform for modeling viral latency and reactivation of human viral pathogens.

The Hippocampal Vulnerability to Herpes Simplex Virus Type I Infection: Relevance to Alzheimer's Disease and Memory Impairment

Herpes simplex virus type 1 (HSV-1) as a possible infectious etiology in Alzheimer’s disease (AD) has been proposed since the 1980s. The accumulating research thus far continues to support the association and a possible causal role of HSV-1 in the development of AD. HSV-1 has been shown to induce neuropathological and behavioral changes of AD, such as amyloid-beta accumulation, tau hyperphosphorylation, as well as memory and learning impairments in experimental settings. However, a neuroanatomical standpoint of HSV-1 tropism in the brain has not been emphasized in detail. In this review, we propose that the hippocampal vulnerability to HSV-1 infection plays a part in the development of AD and amnestic mild cognitive impairment (aMCI). Henceforth, this review draws on human studies to bridge HSV-1 to hippocampal-related brain disorders, namely AD and aMCI/MCI. Next, experimental models and clinical observations supporting the neurotropism or predilection of HSV-1 to infect the hippocampus are examined. Following this, factors and mechanisms predisposing the hippocampus to HSV-1 infection are discussed. In brief, the hippocampus has high levels of viral cellular receptors, neural stem or progenitor cells (NSCs/NPCs), glucocorticoid receptors (GRs) and amyloid precursor protein (APP) that support HSV-1 infectivity, as well as inadequate antiviral immunity against HSV-1. Currently, the established diseases HSV-1 causes are mucocutaneous lesions and encephalitis; however, this review revises that HSV-1 may also induce and/or contribute to hippocampal-related brain disorders, especially AD and aMCI/MCI.

Efficient establishment of reactivatable latency by an acyclovir-resistant herpes simplex virus 1 thymidine kinase substitution mutant with reduced neuronal replication

Herpes simplex virus 1 causes recurrent diseases by reactivating from latency, which requires the viral thymidine kinase (TK) gene. An acyclovir-resistant mutation in TK, V204G, was previously repeatedly identified in a patient with recurrent herpetic keratitis. We found that compared with its parental strain KOS, a laboratory-derived V204G mutant virus was impaired in replication in cultured neurons despite little defect in non-neuronal cells. After corneal inoculation of mice, V204G exhibited defects in ocular replication that were modest over the first three days but severe afterward. Acute replication of V204G in trigeminal ganglia was significantly impaired. However, V204G established latency with viral loads as high as KOS and reactivated with high frequency albeit reduced kinetics. Acyclovir treatment that drastically decreased ocular and ganglionic replication of KOS had little effect on V204G. Thus, despite reduced neuronal replication due to impaired TK activity, this clinically relevant drug-resistant mutant can efficiently establish reactivatable latency.

Glutamine supplementation suppresses herpes simplex virus reactivation

Chronic viral infections are difficult to treat, and new approaches are needed, particularly those aimed at reducing reactivation by enhancing immune responses. Herpes simplex virus (HSV) establishes latency and reactivates frequently, and breakthrough reactivation can occur despite suppressive antiviral therapy. Virus-specific T cells are important to control HSV, and proliferation of activated T cells requires increased metabolism of glutamine. Here, we found that supplementation with oral glutamine reduced virus reactivation in latently HSV-1-infected mice and HSV-2-infected guinea pigs. Transcriptome analysis of trigeminal ganglia from latently HSV-1-infected, glutamine-treated WT mice showed upregulation of several IFN-γ-inducible genes. In contrast to WT mice, supplemental glutamine was ineffective in reducing the rate of HSV-1 reactivation in latently HSV-1-infected IFN-γ-KO mice. Mice treated with glutamine also had higher numbers of HSV-specific IFN-γ-producing CD8 T cells in latently infected ganglia. Thus, glutamine may enhance the IFN-γ-associated immune response and reduce the rate of reactivation of latent virus infection.

Effects of antiviral medications on herpetic epithelial keratitis in mice

PURPOSE

Aciclovir (ACV), valaciclovir (VACV) and famciclovir (FCV) are used for systemic infections caused by herpes virus. In Japan, only topical ACV is permitted for use against herpetic keratitis. We investigated the effectiveness of topical ACV, oral VACV and oral FCV on mouse epithelial herpetic keratitis.

METHODS

C57/BL76 mice were inoculated with HSV-1 McKrae strain in the cornea. Once infection was confirmed 4 days after inoculation, topical ACV, oral VACV and FCV were started and administered for 5 days. Control groups were given either topical or oral saline. On days 2, 4, 6 and 10 after medication started, tears, eyeballs, and trigeminal ganglia were examined using viral culture and real-time PCR.

RESULTS

Viral culture of tears detected no HSV in the topical ACV group on day 4 after administration start; with similar results for the oral VACV group on day 4; and the oral FCV group on day 6. Real-time PCR of the eyeballs showed significant decrease of HSV DNA copy number in the topical ACV group on days 4 and 6 compared to the topical saline group. Real-time PCR of the trigeminal ganglia showed significant decrease of HSV DNA copy number in the oral VACV group on days 4 and 6, and in the oral FCV group on day 6 compared to the oral saline group.

CONCLUSION

We suggest that 5-day administration of topical ACV, oral VACV and oral FCV are effective for mouse epithelial herpetic keratitis and sufficiently decrease HSV amounts in the ocular surface and eyeballs.

Antiviral agents for herpes simplex virus

This review starts with a brief description of herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), the clinical diseases they cause, and the continuing clinical need for antiviral chemotherapy. A historical overview describes the progress from the early, rather toxic antivirals to acyclovir (ACV) which led the way for its prodrug, valacyclovir, to penciclovir and its prodrug, famciclovir (FCV). These compounds have been the mainstay of HSV therapy for two decades and have established a remarkable safety record. This review focuses on these compounds, the preclinical studies which reveal potentially important differences, the clinical trials, and the clinical experience through two decades. Some possible areas for further investigation are suggested. The focus shifts to new approaches and novel compounds, in particular, the combination of ACV with hydrocortisone, known as ME609 or zovirax duo, an HSV helicase-primase inhibitor, pritelivir (AIC316), and CMX001, the cidofovir prodrug for treating resistant HSV infection in immunocompromised patients. Letermovir has established that the human cytomegalovirus terminase enzyme is a valid target and that similar compounds could be sought for HSV. We discuss the difficulties facing the progression of new compounds. In our concluding remarks, we summarize the present situation including a discussion on the reclassification of FCV from prescription-only to pharmacist-controlled for herpes labialis in New Zealand in 2010; should this be repeated more widely? We conclude that HSV research is emerging from a quiescent phase.

The challenge of developing a herpes simplex virus 2 vaccine

HSV infections are prevalent worldwide. A vaccine to prevent genital herpes would have a significant impact on this disease. Several vaccines have shown promise in animal models; however, so far these have not been successful in human clinical studies. Prophylactic HSV vaccines to prevent HSV infection or disease have focused primarily on eliciting antibody responses. Potent antibody responses are needed to result in sufficiently high levels of virus-specific antibody in the genital tract. Therapeutic vaccines that reduce recurrences need to induce potent T-cell responses at the site of infection. With the increasing incidence of HSV-1 genital herpes, an effective herpes vaccine should protect against both HSV-1 and HSV-2. Novel HSV vaccines, such as replication-defective or attenuated viruses, have elicited humoral and cellular immune responses in preclinical studies. These vaccines and others hold promise in future clinical studies.

Sustained CD8+ T cell memory inflation after infection with a single-cycle cytomegalovirus

Cytomegalovirus (CMV) is a β-herpesvirus that establishes a lifelong latent or persistent infection. A hallmark of chronic CMV infection is the lifelong persistence of large numbers of virus-specific CD8+ effector/effector memory T cells, a phenomenon called “memory inflation”. How the virus continuously stimulates these T cells without being eradicated remains an enigma. The prevailing view is that CMV establishes a low grade “smoldering” infection characterized by tiny bursts of productive infection which are rapidly extinguished, leaving no detectable virus but replenishing the latent pool and leaving the immune system in a highly charged state. However, since abortive reactivation with limited viral gene expression is known to occur commonly, we investigated the necessity for virus reproduction in maintaining the inflationary T cell pool. We inhibited viral replication or spread in vivo using two different mutants of murine CMV (MCMV). First, famcyclovir blocked the replication of MCMV encoding the HSV Thymidine Kinase gene, but had no impact on the CD8+ T cell memory inflation once the infection was established. Second, MCMV that lacks the essential glycoprotein L, and thus is completely unable to spread from cell to cell, also drove memory inflation if the virus was administered systemically. Our data suggest that CMV which cannot spread from the cells it initially infects can repeatedly generate viral antigens to drive memory inflation without suffering eradication of the latent genome pool.

Cytomegalovirus (CMV) establishes life-long, asymptomatic infections in healthy people. Ongoing immune surveillance prevents viral disease but also results in the accumulation of large numbers of virus-specific T cells. The mechanisms by which the virus persists while stimulating such strong immune responses are unknown. We and others had hypothesized that periodic viral replication and spread to neighboring cells allowed CMV to replenish the pool of infected cells while stimulating virus-specific T cells to accumulate. In this manuscript, we have tested this model by blocking the replication or spread of murine cytomegalovirus (MCMV) and found, surprisingly, that accumulation of virus-specific T cells occurs independently of viral replication. Moreover, these T cells developed the terminal differentiated phenotype that is indicative of repeated antigenic stimulation. Thus, these data suggest that CMV can remain active and continuously stimulate the immune system, while avoiding immune-mediated clearance, without the capacity to spread from cell to cell.

CMX001 potentiates the efficacy of acyclovir in herpes simplex virus infections

Although acyclovir (ACV) has proven to be of value in the therapy of certain herpes simplex virus (HSV) infections, there is a need for more effective therapies, particularly for serious infections in neonates and immunocompromised individuals, where resistance to this drug can be problematic. CMX001 is an orally bioavailable lipid conjugate of cidofovir that is substantially less nephrotoxic than the parent drug and has excellent antiviral activity against all the human herpesviruses. This compound retains full antiviral activity against ACV-resistant laboratory and clinical isolates. The combined efficacy of CMX001 and ACV was evaluated in a new real-time PCR combination assay, which demonstrated that the combination synergistically inhibited the replication of HSV in cell culture. This was also confirmed in murine models of HSV infection, where the combined therapy with these two drugs synergistically reduced mortality. These results suggest that CMX001 may be effective in the treatment of ACV-resistant HSV infections and as an adjunct therapy in individuals with suboptimal responses to ACV.

Inflation and long-term maintenance of CD8 T cells responding to a latent herpesvirus depend upon establishment of latency and presence of viral antigens

Following the priming and contraction phases of the T cell response, latent persistent herpesviruses lead to an accumulation of large pools of virus-specific CD8 T cells, also known as memory inflation (MI). The mechanism of this inflation is incompletely understood, largely because the molecular reactivation of these viruses in vivo and its impact upon T cell biology have not been resolved in mice, and because the relevant observations in humans remain, by necessity, correlative. Understanding these processes is essential from the standpoint of the proposed critical role for latent herpesviruses in aging of the immune system. We studied the causes of memory CD8 T cell accumulation following systemic HSV-1 administration as a model of widespread latent viral infection in humans. A direct role of viral latency and Ag-specific restimulation in driving the accumulation and maintenance of inflated CD8 T cells and a strongly suggested role of viral reactivation in that process were shown by the following: 1) lack of MI in the absence of established latency; 2) prevention or delay of MI with drugs that curtail viral replication; and 3) abrogation of MI by the transfer of inflated T cells into a virus-free environment. These results strongly suggest that periodic, subclinical reactivations of a latent persistent virus cause dysregulation of memory CD8 T cell homeostasis, similar to the one in humans. Moreover, results with antiviral drugs suggest that this approach could be considered as a treatment modality for maintaining T cell diversity and/or function in old age.

Effect of Oral Valaciclovir on Herpetic Keratitis

PURPOSE

To examine the efficacy of valaciclovir (VACV) oral formulation as an alternative to topical treatments in a case of herpetic keratitis.

METHODS

The patient was a 61-year-old man who presented with dendritic keratitis in his left eye. After recognizing his difficulty in using eye ointment, we prescribed oral VACV 500 mg tablets twice daily for 7 days. We also describe our experiments with orally administered VACV in a mouse model of this disease. In this study, 143 Balb/c mice were inoculated with herpes simplex virus type 1 (HSV)-1 in each eye and treated with oral VACV 50 or 100 mg/kg twice daily, oral acyclovir (ACV) 50 mg/kg 5 times/d, 3% ACV eye ointment (ACV-O) 5 times/d, 3% ACV eye drops 5 times/d, or control for 5 days.

RESULTS

After 7 days, the patient's lesion was observed healed. Corrected left visual acuity was also improved, and HSV DNA was below detectable level. In the mouse study, slit-lamp examination on days 3, 4, 5, and 7 revealed that all 5 ACV and VACV treatment groups were significantly more effective in improving symptoms of herpetic epithelial keratitis versus control (P < 0.05). Moreover, VACV 100 mg/kg was superior to other treatments. Viral titers in mouse eyeball and trigeminal ganglia were lowest in the VACV 100 mg/kg group versus other treatment groups.

CONCLUSION

Our case example suggests that when frequent application, blurred vision, and foreign body sensation after ACV-O application cause difficulty for patients to follow treatment, oral VACV might be an effective and safe option for patients with herpetic keratitis.

Famciclovir

Famciclovir (Famvir) is the oral prodrug of penciclovir, an agent that has demonstrated antiviral activity against herpes simplex viruses, type 1 (HSV-1) and 2 (HSV-2) [which cause orolabial and/or genital herpes simplex], and against varicella zoster virus (VZV) [a reactivation of which leads to herpes zoster]. Famciclovir has efficacy similar to that of aciclovir (in immunocompetent or immunocompromised patients) or valaciclovir (in immunocompetent patients) in the treatment of herpes zoster, and efficacy similar to aciclovir in the treatment of first or recurrent episodes of genital herpes (in immunocompetent or immunocompromised patients). Famciclovir also has efficacy in the suppression of recurrent episodes of genital herpes, and in the treatment of orolabial herpes, in immunocompetent patients. As such, famciclovir is a well tolerated first-line option for the treatment of herpes zoster and the treatment and suppression of genital herpes, and is approved for the treatment of recurrent orolabial herpes. Convenient patient-initiated single-day (for recurrent genital herpes) and single-dose (for orolabial herpes) dosage regimens may contribute to treatment compliance, patient acceptability and subsequent treatment outcomes.

Valacyclovir treatment ameliorates the persistently increased pentylenetetrazol-induced seizure susceptibility in mice with herpes simplex virus type 1 infection

Herpes simplex virus type 1 (HSV-1) is an important pathogen related to epilepsy. We have shown previously that corneal inoculation of mice with HSV-1 causes acute spontaneous behavioral and electrophysiological seizures and increases hippocampal excitability and kainite-induced seizure susceptibility. In this study, we aimed to determine whether early-life HSV-1 infection in mice might cause short- and long-term enhanced susceptibility to pentylenetetrazol (PTZ)-induced seizures and to evaluate whether early antiviral drug therapy was effectively ameliorating this deficit. Seizure threshold was calculated by the latency of onset of the myoclonic jerk, generalized clonus, and maximal tonic-clonic convulsion. We demonstrate that the localization of viral antigens was predominantly within the bilateral temporal areas (amygdala, piriform, and entorhinal cortex) of HSV-1-infected mice. We also present evidence that mice of all HSV-1-infected groups had a shorter latency and higher severity to PTZ-induced seizures than in age-matched, mock-infected controls. Treatment of HSV-1-infected mice with valacyclovir, a potent inhibitor of HSV-1 replication, produced a dose-dependent decrease in the signs of neurological deficits, pathological damages, and PTZ-induced seizure severity. Our results are consistent with the hypothesis that early-life HSV-1 infection leads to persistent enhancement of neuronal excitability in limbic circuits, which could result in an overall increased propensity to induce seizures later in life. Additionally, prompt optimal antiviral therapy effectively decreases seizure susceptibility in HSV-1-infected mice by limiting the level of viral replication and inflammatory response induced by virus. The present study provides not only experimental evidence, but also a new therapeutic strategy in HSV-1-associated human epilepsy.

[The latest in herpes simplex keratitis therapy]

Herpetic keratitis is characterized by spontaneous recurrences and a risk of vision loss, the latter being more serious when relapses are frequent and severe. Two clinical forms are commonly distinguished: epithelial keratitis, usually quickly resolved with topical antivirals, and stromal keratitis, which has a slower progression, even when both steroids and antivirals are used. Great strides have been made during the last 20 Years in the therapy of herpes keratitis, which is now considered and treated as a chronic disease. Randomized controlled studies definitively showed the decrease in spontaneous herpetic ocular events in patients treated with long-term oral acyclovir. The effectiveness of preventive treatment has also been shown during high-risk periods, especially ocular surgery, in patients with a history of herpes keratitis. However, the optimal duration and dosage of antiviral prevention have yet to be defined. We can also hope that in the future novel antiviral strategies such as vaccination will reduce the place of herpes keratitis as an indication for corneal graft.

Axonal transport and sorting of herpes simplex virus components in a mature mouse visual system

The time course for delivery and transport of two major proteins of herpes simplex virus (HSV) has been determined for mature mouse retinal ganglion cell axons in vivo. Twenty-four hours after intravitreal injection of HSV, valacyclovir was introduced into the drinking water of the mice to inhibit subsequent viral replication. Without treatment, viral spread and replication in periaxonal glial cells confound study of axonal transport. At 2 to 5 days after infection, the animals were sacrificed and contiguous segments of the optic pathway were removed. Immunofluorescence microscopy indicated that the number of infected astrocytes was reduced in the proximal optic nerve and eliminated in the optic tract. Western blots of the retina with antibodies for envelope and capsid components, glycoprotein D (gD) and VP5, respectively, revealed that both components were expressed in retinal homogenates by 2 days. Results of reverse transcription-PCR indicated that there was no gD mRNA present in the treated optic tract 5 days after infection. Therefore, we conclude that gD is transcribed from viral mRNA in the retinal ganglion cell bodies. The gD accumulated in the proximal ganglion cell axon by 2 days and reached the most distal segment after 3 days. The VP5 first appeared in the proximal axons at 4 days, about 48 h after the appearance of gD. Thus, gD entered the axon earlier and independent of VP5. These finding confirm the subassembly model of viral transport in neurons and suggest that there is a 4- to 5-day window for initiation of effective antiviral treatment with valacyclovir.

Alpha/Beta interferon and gamma interferon synergize to inhibit the replication of herpes simplex virus type 1

In vivo evidence suggests that T-cell-derived gamma interferon (IFN-gamma) can directly inhibit the replication of herpes simplex virus type 1 (HSV-1). However, IFN-gamma is a weak inhibitor of HSV-1 replication in vitro. We have found that IFN-gamma synergizes with the innate IFNs (IFN-alpha and -beta) to potently inhibit HSV-1 replication in vitro and in vivo. Treatment of Vero cells with either IFN-beta or IFN-gamma inhibits HSV-1 replication by <20-fold, whereas treatment with both IFN-beta and IFN-gamma inhibits HSV-1 replication by approximately 1,000-fold. Treatment with IFN-beta and IFN-gamma does not prevent HSV-1 entry into Vero cells, and the inhibitory effect can be overcome by increasing the multiplicity of HSV-1 infection. The capacity of IFN-beta and IFN-gamma to synergistically inhibit HSV-1 replication is not virus strain specific and has been observed in three different cell types. For two of the three virus strains tested, IFN-beta and IFN-gamma inhibit HSV-1 replication with a potency that approaches that achieved by a high dose of acyclovir. Pretreatment of mouse eyes with IFN-beta and IFN-gamma reduces HSV-1 replication to nearly undetectable levels, prevents the development of disease, and reduces the latent HSV-1 genome load per trigeminal ganglion by approximately 200-fold. Thus, simultaneous activation of IFN-alpha/beta receptors and IFN-gamma receptors appears to render cells highly resistant to the replication of HSV-1. Because IFN-alpha or IFN-beta is produced by most cells as an innate response to virus infection, the results imply that IFN-gamma secreted by T cells may provide a critical second signal that potently inhibits HSV-1 replication in vivo.

Progress in meeting today's demands in genital herpes: an overview of current management

Treatment of genital herpes requires accurate diagnosis, patient support, and effective treatment. Diagnosis is usually straightforward for classic presentations characterized by vesicular lesions but can be challenging for atypical presentations, which are more common. Diagnosis of asymptomatic infection requires access to molecular technology or type-specific serologic assays. Misconceptions about herpes simplex infection are common and patient education is essential. Patient concerns extend beyond disease frequency and severity-the psychological impact should not be underestimated. Antiviral therapy is relevant at all stages of infection. Acyclovir, valacyclovir, and famciclovir are effective and well tolerated for genital herpes treatment. Continuous suppressive therapy controls all symptoms of recurrent disease and helps to relieve disease complications. The prodrugs valacyclovir and famciclovir offer easier, less-frequent dosing than required for acyclovir. Valacyclovir achieves effective suppression when taken once a day. Interventions to prevent genital herpes transmission and to control the global problem are urgently required.

Potent in vivo antiviral activity of the herpes simplex virus primase-helicase inhibitor BAY 57-1293

BAY 57-1293 belongs to a new class of antiviral compounds and inhibits replication of herpes simplex virus (HSV) type 1 and type 2 in the nanomolar range in vitro by abrogating the enzymatic activity of the viral primase-helicase complex. In various rodent models of HSV infection the antiviral activity of BAY 57-1293 in vivo was found to be superior compared to all compounds currently used to treat HSV infections. The compound shows profound antiviral activity in murine and rat lethal challenge models of disseminated herpes, in a murine zosteriform spread model of cutaneous disease, and in a murine ocular herpes model. It is active in parenteral, oral, and topical formulations. BAY 57-1293 continued to demonstrate efficacy when the onset of treatment was initiated after symptoms of herpetic disease were already apparent.

Lack of effect of treatment with penciclovir or acyclovir on the establishment of latent HSV-1 in primary sensory neurons in culture

Recent studies suggest reductions in establishment of herpes simplex virus, type 1 (HSV-1) latency using the nucleoside analog penciclovir compared with acyclovir in the murine model. These observations raise the possibility that the new analogs may have novel activities that directly interfere with the establishment of the latent infection, suggesting a mechanism other than simply blocking the productive infection. To determine if penciclovir has a direct action on the establishment of latency, we compared the effects of penciclovir versus acyclovir in an in vitro model of HSV-1 latency in rat dorsal root ganglia neurons in culture. In neurons in culture, both penciclovir and acyclovir were highly effective in blocking the productive infection. However, neither penciclovir nor acyclovir blocked establishment of latency as demonstrated by similar percentages of neurons expressing the latency-associated transcript (LAT). Following removal of the respective nucleoside analog, latency was maintained until reactivation was induced by nerve growth factor deprivation. Similar virus titers were recovered after induction of reactivation of latent infections, which were established in the presence of either penciclovir or acyclovir. These results indicate that neither penciclovir nor acyclovir treatment directly prevents the establishment of latent HSV-1 infections in primary sensory neurons in culture.

Effect of famciclovir on herpes simplex virus type 1 corneal disease and establishment of latency in rabbits

Famciclovir (FCV) is efficacious in the treatment of acute herpes zoster and recurrent genital infections but has not been used to treat ocular herpes simplex virus (HSV) infections. We evaluated the efficacy of orally administered FCV in treating HSV-1 epithelial keratitis and determined its effects on the establishment of latency and subsequent reactivation. Rabbits were inoculated with HSV-1 strain 17 syn+ and treated twice daily with increasing concentrations of FCV (60 to 500 mg/kg of body weight). This resulted in a significant, dose-dependent improvement in keratitis scores, as well as prolonged survival. Regardless of the dose of drug used, all groups exhibited the high rates of spontaneous and induced reactivation characteristic of 17syn+. The efficacy of 250 mg of FCV per kg was also compared to topical treatment with 1% trifluorothymidine (TFT). Although TFT treatment was more effective at reducing eye disease, FCV-treated rabbits had a better survival rate. Real-time quantitative PCR analysis of rabbit trigeminal ganglia (TG) demonstrated that FCV significantly reduced the HSV-1 copy number compared to that after treatment with TFT or the placebo but not in a dose-dependent manner. In summary, oral FCV treatment significantly reduces the severity of corneal lesions, reduces the number of HSV-1 genomes in the TG, improves survival, and therefore may be beneficial in reducing the morbidity of HSV keratitis in the clinic.

Gamma interferon impedes the establishment of herpes simplex virus type 1 latent infection but has no impact on its maintenance or reactivation in mice

Murine models of gamma interferon (IFN-gamma) deficiency demonstrate the role of this cytokine in attenuating acute herpes simplex virus (HSV) disease; however, the effect of IFN-gamma on the establishment and maintenance of neuronal latency and viral reactivation is not known. Using the IFN-gamma knockout (GKO) model of IFN-gamma deficiency and sensitive quantitative PCR methods, we show that IFN-gamma significantly reduces the ganglion content of latent HSV-1 in BALB/c mice, which in turn delays viral time to reactivation following UV irradiation. Similar effects were not seen in the C57BL/6 strain. These results indicate that IFN-gamma significantly attenuates latent HSV infection in the mouse model of ocular infection but has no impact on the maintenance of latency or virus reactivation.

Further evidence from a murine infection model that famciclovir interferes with the establishment of HSV-1 latent infections

Mice were infected with herpes simplex virus type 1 (HSV-1) via the ear pinna. Famciclovir therapy was commenced on days 2-7 post infection (p.i.). The ipsilateral and contralateral trigeminal (TG) and third cervical ganglia (CIII) from individual mice were tested for latency 1 and 6 months after infection by explant culture or in situ hybridization for latency-associated transcripts (LAT). There were significantly fewer LAT-positive neurons in ipsilateral and contralateral TG (but not CIII) when therapy was delayed by up to 6 days. There was a low correlation between the number of LAT-positive neurons and reactivation by explant culture. Latency data for individual ganglia, compared with those from previous studies, allow us to rationalize differences between the effects of nucleosides on the establishment of latency in different anatomical sites and when tissues are evaluated using different techniques. The implications of the findings for the use of famciclovir to counter HSV latency in humans are addressed.

Valaciclovir: a review of its long term utility in the management of genital herpes simplex virus and cytomegalovirus infections

Valaciclovir is an aciclovir prodrug used to treat infections caused by herpes simplex virus (HSV) and varicella zoster virus, and for prophylaxis against cytomegalovirus (CMV). Oral valaciclovir provides significantly better oral bioavailability than oral aciclovir itself, contributing to the need for less frequent administration. Several studies have demonstrated the efficacy of long term (> 90 days) therapy with valaciclovir for the suppression of genital HSV disease in otherwise healthy individuals with HSV infection. In 1 randomised, double-blind trial, once daily valaciclovir (1000 mg, 500 mg and 250 mg) produced statistically significant suppression of disease recurrence, as did twice daily valaciclovir 250 mg and aciclovir 400 mg. Valaciclovir dosages of > or = 500 mg daily are recommended for suppression of genital herpes recurrences in immunocompetent individuals. This disease occurs frequently in patients with human immunodeficiency virus (HIV) infection and, in a single randomised double-blind trial, prophylactic valaciclovir (1000 mg once daily or 500 mg twice daily) and aciclovir (400 mg twice daily) were found to be of similar efficacy in the suppression of genital herpes. However, a higher than expected dropout rate indicated that more studies of valaciclovir in patients with HIV are required. In a randomised trial of patients undergoing renal transplant, valaciclovir 2 g 4 times daily for 90 days significantly reduced the incidence and delayed the onset of CMV disease: the incidence in valaciclovir-treated patients who were CMV-seronegative at baseline, and recieived a kidney from a CMV-seropositive donor, was 3% versus 45% for placebo after 90 days of treatment. Acute graft rejection was also reduced in the valaciclovir-treated group. A small study in heart transplant patients compared valaciclovir (2 g 4 times daily) with aciclovir (200 mg 4 times daily) and found a significant reduction in CMV antigenaemia favouring valacilovir at the end of the treatment period. Additional reductions in other indices of CMV in those given valaciclovir compared with aciclovir were also noted. In a preliminary study of prophylaxis for CMV disease in bone marrow transplant recipients valaciclovir (2 g 4 times daily) was superior to aciclovir (800 mg 4 times daily) in terms of time to CMV viraemia or viruria. Although valaciclovir (8 g/day for approximately 30 weeks) reduced the incidence and time to CMV disease compared with aciclovir (3.2 g/day) in patients with advanced HIV disease, valaciclovir was associated with more gastrointestinal complaints and an increased risk of death, leading to premature termination of the study. As yet, no trials comparing the efficacy of valaciclovir with famciclovir (the oral prodrug for penciclovir) in the suppression of recurrent episodes of genital herpes have been published, nor have direct comparisons been made, between valaciclovir with ganciclovir in patients with CMV disease. Valaciclovir is well tolerated at dosages used to suppress recurrent episodes of genital herpes (500 to 1000 mg/day) in immunocompetent and HIV seropositive individuals, with headache being reported most often. However, a potentially fatal thrombotic microangiopathy (TMA)-like syndrome has been reported in some immunocompromised patients receiving high-dose prophylactic valaciclovir therapy (8 g/day) for CMV disease for prolonged periods, and the risk of this syndrome appears to be higher in patients with advanced HIV disease. While the clinical benefits of valaciclovir in some immunocompromised patients may outweigh the risk of TMA, close monitoring for symptoms of TMA is indicated in all immunocompromised patients receiving high-dose valaciclovir.

CONCLUSION

Oral valaciclovir is an effective drug for the suppression of recurrent episodes of genital herpes in immunocompetent and immunocompromised individuals. (ABSTRACT TRUNCATED)

Early therapy with valaciclovir or famciclovir reduces but does not abrogate herpes simplex virus neuronal latency

Mice were infected via the ear pinna using a recombinant strain of HSV-1 expressing the beta-gal gene under the LAT promoter. Mice were treated continuously with valaciclovir or famciclovir, from 1 day before or 1 day after virus inoculation for 10 days. Ipsilateral and contralateral trigeminal and cervical ganglia were later assessed by co-cultivation or for X-Gal-positive or LAT-positive neurons. Latency was markedly reduced by early therapy, however, a basal level of HSV-1-positive neurons was detected in all mice.

Lack of interleukin-6 (IL-6) enhances susceptibility to infection but does not alter latency or reactivation of herpes simplex virus type 1 in IL-6 knockout mice

The ability of the pleotropic, proinflammatory cytokine interleukin-6 (IL-6) to affect the replication, latency, and reactivation of herpes simplex virus type 1 (HSV-1) in cell culture and in IL-6 knockout (KO) mice was studied. In initial studies, we found no effect of exogenous IL-6, monoclonal antibodies to IL-6, or monoclonal antibody to the IL-6 coreceptor, gp130, on HSV-1 replication in vitro by plaque assay or reactivation ex vivo by explant cocultivation of latently infected murine trigeminal ganglia (TG). Compared with the wild-type (WT) mice, the IL-6 KO mice were less able to survive an ocular challenge with 10(5) PFU of HSV-1 (McKrae) (40% survival of WT and 7% survival KO mice; P = 0.01). There was a sixfold higher 50% lethal dose of HSV-1 in WT than IL-6 KO mice (1.7 x 10(4) and 2.7 x 10(3) PFU, respectively). No differences were observed in titers of virus recovered from the eyes, TG, or brains or in the rates of virus reactivation by explant cocultivation of TG from latently infected WT or KO mice. Exposure of latently infected mice to UV light resulted in comparable rates of reactivation and in the proportions of WT and KO animals experiencing reactivation. Moreover, quantitative PCR assays showed nearly identical numbers of HSV-1 genomes in latently infected WT and IL-6 KO mice. These studies indicate that while IL-6 plays a role in the protection of mice from lethal HSV infection, it does not substantively influence HSV replication, spread to the nervous system, establishment of latency, or reactivation.