Recent advance in management of herpes simplex in Japan

Herpes simplex, a common infection caused by the herpes simplex virus (HSV), is transmitted through contact of the skin/mucous membrane and establishes latency in the sensory ganglia for the rest of the life of the host. HSV occasionally reactivates and forms blisters around the lips or genitalia in some patients. Repeated overt symptoms, and, much more frequent, subclinical reactivation in the mucosa, make the host retain anti‐HSV immunity continuously, resulting in maintaining steadily elevated antibody titer at any point after infection. Clinical symptoms differ in primary infection and recurrence. Primary infections sometimes manifest as severe symptoms such as fever and lymphadenopathy in addition to blisters/erosions of the skin, gingiva, lips, and oral mucosa, while recurrent herpes is generally mild. Diagnosing typical herpes simplex is not difficult, but when the course and manifestations are typical, definitive tests to identify HSV infection are limited since serology is not useful except with primary infection. For treatment, safe and effective oral antiviral drugs are available. Patient‐initiated therapy is a new method of administration labeled in Japan. Amenamevir, an inhibitor of viral helicase primase, is available in Japan and labeled in addition to herpes zoster. These new diagnostic and therapeutic tools should be used for better management of herpes simplex.


| INTRODUC TI ON
There are nine known human herpes viruses, two of which are herpes simplex virus (HSV) type 1 and type 2. 1,2 With varicella zoster virus (VZV) added, these three viruses make alphaherpesvirinae. 1 HSV is transmitted through the mucous membrane or damaged skin and establish latent infection in the ganglia of sensory neurons. 3 Fever, menstruation, and sun exposure cause HSV-1 to form recurrent lesions, mainly on the lips and the face, and sexual intercourse often cause HSV-2 to produce recurrent lesions, mainly around the genital area. These recurrences manifest generally mild symptoms but can be severe depending on the background disease of the host. This article will briefly describe the lifecycle of HSV, followed by the clinical and laboratory findings including diagnostic tests and the corresponding treatment.

| LIFEC YCLE OF H S V: LE SSON S LE ARNED FROM THE S EROLOGY
HSV widely infects populations worldwide. 4 Recent epidemiological research estimates that 66.6% and 13.2% of the world's populations is infected with HSV-1 and HSV-2, respectively. 4 Serum antibody titer studies in Japan have shown that its positivity increases in direct proportion to age (Figure 1). 5 This tendency was commonly observed for all clinical specimens collected from different groups, such as those from a population survey, those from patients who visited hospitals or dermatology clinics, and commercial laboratory test samples. The positive serology assures past infection of a large proportion of the population, but a limited portion of such patients manifest symptoms of herpes simplex. In a large nationwide survey 6 for outpatients in Japan, herpes simplex accounted for 1.02% of outpatient visits. As a viral disease, the number was less than that of herpes zoster, which is usually a once in a lifetime event. This reversal phenomenon indicates that many patients who are HSVseropositive do not have symptoms and only a limited population needs medication. In addition, HSV is not transmitted from a patient at the time of overt symptoms but mostly through asymptomatic viral shedding. In other words, herpes simplex as a "disease" is not a necessary condition required for HSV to survive in humans. 7 Unlike herpes zoster, the number of patients who develop the disease is constant by age 6 ( Figure 2). The same trend can be seen worldwide. 4 The fact that the HSV-seropositive population increases linearly with age means that most humans are infected at least once over the years. This fact also secures that living with HSV is a normal human condition and may also prove that infection with HSV does not affect the longevity of the host, although there is no controlled data.

| D IAG NOS IS OF HERPE S S IMPLE X
Herpes simplex is not difficult to diagnose as long as the clinical manifestations are typical. However, there are various perioral or perigenital diseases other than herpes and when a case is not decisive, we suddenly struggle with finding methods to accurately identify HSV in our practice. This is partly because serological tests are not functional for diagnostic purpose as mentioned above. HSV antibody titers become positive in most patients as they get older, hence positive serology does not secure that the presenting symptoms indicate herpes. Also, in the case of recurrent herpes, paired antibody titers before and after the onset of symptoms hardly change. This observation indicates that HSV recurs under maintained immunity against the virus.
Serological tests for HSV are only beneficial for diagnosis in the following cases. At primary infection, detection of the HSV-specific IgM antibody is definitive. Caution must be paid to the fact that anti-HSV-IgM titers can be negative in the very early stage of HSV infection (a few days after onset) and may also be very low after 1 month. Serology is functional in excluding recurrent herpes. When the HSV-specific IgG antibody is negative on a sensitive test such as an enzyme-linked immunosorbent assay, it is least likely that the patient has recurrent herpes simplex. However, one must be careful that a negative IgG antibody can be seen in an early case of primary infection. Another pitfall is a negative result with less sensitive tests such as the complement fixation test. A positive but low IgG titer may sometimes provide a false-negative complement fixation result.
To confirm the diagnosis, some components of HSV needs to be identified from the lesion. Usually, antigen or DNA of HSV are the targets for this pupose.
One of the antigen testing methods currently available in Japan is immunofluorescent staining. In this method, a smear from the lesions is stained with HSV glycoprotein-specific antibodies labeled with fluorescence. Test kits are available but judging the positivity requires a certain level of experience. Outsourcing of this test can take a few days until the results are available. Rapid test kits using immunochromatography is also available. Like other kits for viral/ bacterial antigens, these kits provide results in 10 min with a simple procedure; hence, they are useful for decision-making regarding treatment. The fluorescent antibody method on smears can distinguish HSV-1 and HSV-2, while currently available rapid test kits are all type common. However, type discrimination is generally not a clinical necessity. Both immunofluorescent and rapid test kits are labeled by authority and are reimbursed by insurance, but rapid tests can only be reimbursed for the purpose of diagnosing herpetic keratitis and genital herpes, not for the diagnosis of oral herpes.

F I G U R E 1
Incidence of complement fixation test titers against herpes simplex virus by age brackets. Note that the incidence linearly increases with age and most of the patients have 16 -64× titer. Previously unpublished data.

F I G U R E 2
Histograms of the number of patients by age brackets with herpes simplex and herpes zoster in the national survey of Japan. Note that patients with zoster increase sharply from age 50, while those with herpes simplex stays constant at all ages. Adapted from reference [6].
To identify HSV-DNA in the lesions, gene amplification methods such as polymerase chain reaction (PCR) method are used.

Loop-mediated isolation amplification (LAMP), a chain reaction
amplification that does not require thermal cycles, is also used as a gene amplification method other than PCR. We have used the LAMP method to detect HSV in lesions from patients and in asymptomatic buccal mucosa and found that LAMP was almost as sensitive as real-time PCR, which is the most sensitive method Note that this clinical rule, no mucosa-limited lesions, does not apply to primary infections in which the host has no immunity to HSV.

| HERPE S S IMPLE X AND RECENT IMMUN OMO DUL ATORY DRUG S/IMMUN O D E F I C I E N C Y
It is well-known that recurrence of HSV occurs more frequently in immunosuppressed patients. Recently, a variety of immunomodulating agents have been developed for various immune-related diseases and generally they are very effective. Especially, surprisingly rapid expansion of Janus kinase (JAK) inhibitors against various diseases (rheumatoid arthritis, [8][9][10][11][12][13] psoriatic arthritis, 14,15 atopic dermatitis, [16][17][18] ulcerative colitis, 19,20 and more) brought extraordinary incidence of herpes zoster in patients with such diseases. [21][22][23][24][25] Unlike other immunosuppressants, JAK inhibitors induce herpes zoster specifically without much increase of other infections. 26 Naturally, the following question arises. Does the use of JAK inhibitors increase the incidence of herpes simplex as well as herpes zoster? When assessing this question, one must be aware that the incidence of herpes simplex differs among the disease groups. 27 For example, patients with atopic dermatitis have a higher frequency and severity of herpes to begin with. 28 Eczema herpeticum is a severe form of herpes simplex, manifesting disseminative eruption of herpes on the skin, also called Kaposi varicelliform eruption. Risk factors of eczema herpeticum are more severe skin disease and a more evident Th2 shift (increased eosinophil count, serum IgE, and reduced interferon levels). 28 Therefore, dermatologists should see more herpes in patients with severe atopic dermatitis treated with JAK inhibitors, but the question is whether it is attributable to the drug. In clinical trials of atopic dermatitis, eczema herpeticum were observed in upadacitinib-treated patients (1%) but also with placebotreated patients. 17 Caution needs to be paid to these seemingly similar numbers. Upadacitinib provided tremendous improvement over placebo on the skin symptoms of patients with atopic eczema, but still has the same incidence of eczema herpeticum. In addition, in the upadacitinib versus dupilumab trial, 29 incidence of eczema herpeticum was higher in the upadacitinib-treated group. Considering that both upadacitinib and dupilumab are highly effective for skin symptoms of atopic dermatitis, upadacitinib may increase the incidence of eczema herpeticum because of its pharmacological effect. For other JAK inhibitors for atopic dermatitis, more real-world data is required.
For a more valid estimation, a well-balanced control group is needed.
Ideally, the control group would include patients with severe atopic dermatitis treated with other reagents such as dupilumab.
There are more drugs known to induce herpes zoster. Herpes zoster is also more frequently seen in patients treated with anifrolumab, 30 an interferon α receptor inhibitor for systemic lupus erythematosus, or bortezomib, 31,32 a proteasome inhibitor for multiple myeloma. However, the clinical trials of these drugs do not show specific changes in the incidence of herpes simplex compared with the placebo group, 30,31 indicating that the reactivation mechanism of VZV and HSV is different.
Other well-known risk populations for herpes simplex include neonates, HIV-infected congenitally immunocompromised or medically immunosuppressed, and herpes-specific-immunodeficient patients. 33,34 Herpes simplex becomes more frequent and severe among patients with general immunodeficiency. Although rare, some HSV-specific immunodeficiencies are also known. Toll-like receptor 3 is an important innate immune pattern recognition receptor that detects viral nucleic acids in cellular vesicles, and the loss of function mutations of the receptor, 35,36 signal transduction proteins, 33,34 or transportation protein 37 are associated with increased susceptibilities of herpes encephalitis, but patients with herpes encephalitis usually do not have severe cutaneous herpes. The susceptibility of severe herpes on the skin had not been revealed until Bin et al. 38 found candidate genes, SIDT2 and RBBP8NL, by whole genome sequencing of patients with atopic dermatitis with or without eczema herpeticum. Patients with atopic dermatitis with minor alleles of SIDT2 and RBBP8NL showed a higher incidence of eczema herpeticum. Further functional analyses will be needed, but these data suggest that eczema herpeticum is not simply attributable to the impaired barrier function (they found no difference in filaggrin mutation in patients with or without eczema herpeticum) but other immunological assays.

| TRE ATMENT OF HERPE S S IMPLE X
Most recurrent herpes simplex, oral or genital, are mild and heal spontaneously. Therefore, the significance of treatment is to shorten the duration of the disease, and antiviral reagents help this purpose.
On the contrary, primary infection with HSV sometimes manifests as systemic symptoms such as fever and fatigue as well as lesional blisters/erosions and lymphadenopathy. Antiviral therapy is more beneficial in these conditions, although the treatment cannot prevent the establishment of the latent infection. In patients with genital herpes, continuous antiviral therapy has another significance, namely, the prevention of recurrence and reduction in the chance of transmission. 39 The basic policy of treatment of herpes remains the same: early systemic administration of antiviral reagents.
Effective and safe systemic antivirals have been developed for HSV. The main mechanism of anti-HSV drugs belongs to nucleic acid analogues that inhibit viral DNA polymerization. Acyclovir is the most representative antiherpesvirus reagent. Acyclovir serves as a viral DNA polymerase inhibitor in triphosphate form. 40 The phosphorylation is mediated by HSV or VZV's viral enzymes called thymidine kinase, which also phosphorylates other deoxyribonucleosides than thymidine. With this brilliant system, acyclovir has unprecedent specificity for HSV and VZV, resulting in the very safe and effective profile. 41,42 Penciclovir is a similar nucleic acid analog. 43 Acyclovir and penciclovir were modified for better oral absorption, and prodrugs of these two, valacyclovir and famciclovir, respectively replaced their originals in the market for oral use. 44 In Japan, valacyclovir is usually administered at a dose of 500 mg twice daily for 5 days and famciclovir at 250 mg three times daily for 5 days for herpes simplex. [45][46][47] The large proportion of patients with oral or genital herpes can notice the onset of the disease with tingling, nerve pain-like prodromal symptoms before the virus make blisters on the skin. For Famciclovir, 1000 mg (four tablets) is administered twice with a duration of 12 h, so treatment is completed in 1 day. This allows earlier treatment, better compliance, and less total dosage (conventional treatment is three tablets × 5 days), benefiting patients. It should be noted, however, that the treatment is limited to patients who notice the prodromal symptoms.

Amenamevir, is a new antiherpesvirus reagent developed in
Japan. 49,50 Amenamevir inhibits the helicase-primase complex of HSV and VZV. 50,51 The helicase-primase is a viral enzyme that unwinds double-stranded DNA, the genome of HSV, and makes short complementary RNA called a primer to initiate DNA synthesis. 52 Inhibition of this enzyme blocks the replication of HSV/VZV. 51,52 Amenamevir also suppresses the acyclovir-resistant strain of HSV and VZV. 53 Amenamevir is currently available and labeled only for herpes zoster in Japan but is now being developed for the treatment of herpes simplex. 54,55 The efficacy and safety of amenamevir against HSV have already been confirmed in two independent clinical trials for oral 54 and genital 55 herpes, respectively, with patient-initiated therapy format. The dosage and administration of amenamevir is 1200 mg only once, which should contribute to improved compliance.
Suppression therapy for patients with genital herpes in Japan consists of continuous oral administration of one 500-mg tablet of valacyclovir once daily. 56 This method is proven to reduce the frequency of asymptomatic viral shedding and the risk of infection. 56 In Japan, few patients experience relapse with clinical symptoms with this suppression therapy. However, since relapses may occur after discontinuation of this therapy, physicians need to educate recipients that the goal of this treatment is symptomatic suppression of disease onset, not complete cure by eliminating HSV latent in the nerves.

| TRE ATMENT OF S E VERE HERPE S S IMPLE X
As noted above, primary infection of HSV can be severe with widespread lesions on the skin and/or mucosa with systemic symptoms such as fever, fatigue, and lymphadenopathy. Eczema herpeticum is a severe dissemination of herpes simplex on the skin of patients with impaired barrier function of the keratinous layer. These conditions include severe atopic dermatitis, Darier disease, 57 Hailey-Hailey disease, 58 pemphigus, 59 and other congenital/acquired problems of barrier functions. Eczema herpeticum is seen in patients with atopic dermatitis as a primary infection of HSV, but repeated symptoms are also seen in patients with uncontrolled skin symptoms. 27,28 Herpes simplex virus can be severe and intractable in HIVinfected patients with low CD4-positive lymphocyte counts, 60 immunocompromised patients such as bone marrow transplant recipients, 61,62 patients in the late stages of cancer, 63 and patients with uncontrolled severe atopic dermatitis. Consider acyclovir infusion for severe HSV infections in such patients. The ypical dosage is as follows: infusion of 250 mg of acyclovir, three times daily every 8 h, but note that acyclovir is renally excreted, and the dosage should be adjusted according to renal function.

| CON CLUS ION
Finally, the most important thing in the management of herpes simplex is knowledge. Herpes is not the only disease that occurs in the lips and perigenital area. However, some patients are inaccurately diagnosed, believing they have herpes when they do not, and are treated with over-the-counter drugs without necessity. Many | 303 IMAFUKU patients, especially those with genital herpes, feel regret and depression because they believe they have an "incurable" disease; HSV is a universal virus that affects half of the world's population, and suppression therapy is available for genital herpes. Correct diagnosis, comprehensive explaination, and counteracting misconceptions is as important as antiviral therapy in helping patients.

ACK N OWLED G M ENTS
I thank Dr Motoko Miyachi and Ms.Hiroko Imayoshi for all of the DNA testing of HSV samples.

CO N FLI C T O F I NTE R E S T S TATE M E NT
None declared.