Herpes Simplex Virus Infection Disease Background

Introduction

Herpes simplex virus type 1 (HSV-1) and HSV type 2 (HSV-2) are common infections worldwide, being a major health problem. There is a noted wide diversity in the clinical spectrum of herpes simplex virus disease.

Epidemiology

Globally, HSV-1 infection affects approximately 3.8 billion individuals under 50 years of age and approximately 520 million in 15- to 49-year-old individuals are infected with HSV-2. Orolabial herpes simplex virus disease occurs most commonly in children <5 years old. In the United States, there are 572,000 new cases of genital ulcers annually, with 11.9% of people ages 14 to 49 infected with HSV-2. The prevalence of HSV-1 is noted to be highest among low- and middle-income countries. Most WHO regions would have a seroprevalence for HSV-1 exceed 70% for those ages 40 to 49 years old. HSV-1 infection occurs equally between sexes and without any seasonal variation.  

In a systemic review done in Asia, the noted seroprevalence of HSV-1 is as high as 50% for children and 76.5% for adults; the age group infected the most was those aged ≥20. In the case of HSV-2, the pooled mean seroprevalence in Asia was 12.1% for the general population. Reflecting its transmission, the seroprevalence of HSV-2 is highest among men who have sex with men, female sex workers, human immunodeficiency virus (HIV)-positive patients, and sexually transmitted infection (STI) clinic attendees.  

Pathophysiology

Transmission is through direct contact with sores, saliva, or areas around the mouth of actively shedding individuals encourage transmission of HSV-1; the incubation period ranges from 2-12 days. HSV-2 virus is typically transmitted during sexual intercourse through direct contact of genital or anal surfaces, skin, sores or fluids. The virus is transmitted through close contact with individuals who have active viral shedding.    

The virus must come in contact with mucosal surfaces or abraded or damaged skin for infection to be initiated. First, the virus undergoes replication at the site or primary infection, then it is carried to the dorsal root ganglia via retrograde transport; in this area, latency is established. Once latency is established, the right stimulus may cause reactivation; the virus becomes evident at mucocutaneous sites, accompanied by vesicles or ulcers.

Classification

Primary Herpes Simplex Virus Infection

Primary herpes simplex virus infection refers to the first infection with either HSV-1 or HSV-2 in individuals who do not have antibodies to either HSV-1 or HSV-2.

First Episode – Non-primary Infection

First episode – non-primary infection is infection with either HSV-1 or HSV-2 in individuals who have previously existing antibodies against HSV-1 or HSV-2 respectively.

Recurrent Herpes Simplex Virus Infection

Recurrent herpes simplex virus infection results from reactivation of the latent virus. This is usually brought about by triggering factors (eg ultraviolet [UV] light, immunosuppression, trauma, stress, febrile illness). This is less severe and becomes less frequent with time.

Orolabial Herpes Simplex Virus Disease

Most orolabial lesions are caused by HSV-1 but may also be caused by HSV-2. HSV-1 also causes most cases of eye and digital herpetic infections. Recurrent disease tends to occur more frequently with HSV-1 infection than HSV-2.

Genital Herpes Simplex Virus Disease

HSV-2 is usually the cause of herpes genitalis but HSV-1 may occur in up to 1/3 of new cases. HSV-1 tends to cause fewer recurrences and milder disease than HSV-2. Genital herpes simplex virus disease typically occurs in adults; usually transmitted through sexual contact. The incubation period is 2 days to 2 weeks after exposure; primary lesions appear 4 to 7 days after contact.