Herpes Simplex: Background, Microbiology, Pathophysiology

Frequency

United States

HSV is the most common cause of genital ulcers in the United States. HSV-1 is usually acquired in childhood by contact with oral secretions that contain the virus. The presence of HSV-2 can be used as an indirect measure of sexual activity. Seroprevalence rates do not reflect how many of these individuals have or will have symptomatic episodes of HSV recurrence, as the presence of antibodies is poorly correlated with disease protection. Epidemiology of HSV-1 infection in the US is undergoing a remarkable and subtle transition, with less exposure in childhood and more in adulthood, and less oral acquisition but more genital acquisition. [4] HSV-1 could be overtaking HSV-2 as the main cause of first episode of genital herpes in the United States and elsewhere. [5, 6] In a study of college students in the US, the percentage of genital herpes attributed to HSV-1 (as opposed to HSV-2) increased from 31% in 1993 to 78% in 2001. [6]

Seroprevalence:

Based on the National Health and Nutrition Examination Survey (NHANES) during 2015–2016, prevalence of herpes simplex virus type 1 (HSV-1) was 47.8%, and prevalence of herpes simplex virus type 2 (HSV-2) was 11.9%. Prevalence of both HSV-1 and HSV-2 increased with age.Antibodies to HSV-1 increase with age starting in childhood and correlate with socioeconomic status, race, and cultural group. By age 30 years, 50% of individuals in a high socioeconomic status and 80% in a lower socioeconomic status are seropositive. Antibodies to HSV-2 begin to emerge at puberty, correlating with the degree of sexual activity. More than 90% of adults have antibodies to HSV-1 by the fifth decade of life. [1] ​A slight crossover of immunity occurs between HSV-1 and HSV-2, allowing for milder subsequent infection by the partner virus type.

International

HSV is well distributed worldwide, with over 23 million new cases per year. An increase in seroprevalence of antibodies to HSV-2 has been documented throughout the world (including the United States) over the last 20 years. [1]

Mortality/Morbidity

Morbidity and mortality rates associated with HSV infections are discussed in Complications. Overall, the mortality rate associated with herpes simplex infections is related to 3 situations: perinatal infection, encephalitis, and infection in the immunocompromised host.

Race

HSV-2 is most prevalent among non-Hispanic blacks (40.3%) compared with the members of other US racial/ethnic groups; 13.7% among non-Hispanic whites and 11.9% among Mexican Americans. [7]

Sex

Seropositivity to HSV-2 is more common in women (25%) than in men (17%). [8]

Age

HSV-1 infections transmitted via saliva are common in children, although primary herpes gingivostomatitis can be observed at any age. HSV-2 infections are clustered perinatally (from a maternal episode at delivery) and primarily once sexual activity begins. HSV-2 genital infections in children can be an indication of sexual abuse. Increased age (after onset of sexual activity) and total number of sexual partners are independent factors associated with increased seroprevalence of HSV-2 antibodies. [8]