HSV is caused by Herpesvirus hominis (HVH), a widespread infectious agent that causes two serologically distinct HSV types. HSV-1 is transmitted primarily by contact with oral secretions. It mainly affects oral, labial, ocular, or skin tissue. HSV-2, transmitted primarily by contact with genital secretions, mainly affects genital structures. Infection with HSV-1 occurs more frequently and earlier in life than infection with HSV-2. More than 90% of adults have antibodies to HSV-1 by age 40. However, in lower socioeconomic groups, most people acquire HSV-1 by age 20. Antibodies to HSV-2 aren’t routinely detected before puberty.

About 85% of all HVH infections are subclinical; the others produce localized lesions and systemic reactions. After the first infection, the patient is a carrier and susceptible to recurrent infections, which may be provoked by fever, menses, stress, heat, and cold. However, the patient usually has no constitutional signs and symptoms in recurrent infections.

Primary (or initial) HSV infection during pregnancy can lead to abortion, premature labor, microcephaly, and uterine growth retardation. Congenital herpes transmitted during vaginal birth may produce a subclinical neonatal infection or severe infection with seizures, chorioretinitis, skin vesicles, and hepatosplenomegaly.

In infants, HSV-1 can cause life-threatening nonepidemic encephalitis. Primary HSV infection is a leading cause of gingivostomatitis in children ages 1 to 3.

Blindness may result from ocular infection. Females with HSV-2 may be at increased risk for cervical cancer. Urethral stricture may result from recurrent genital herpes.

Perianal ulcers, colitis, esophagitis, pneumonitis, and various neurologic disorders resulting from HSV infection are serious complications in patients with AIDS and other immunocompromised conditions. Viremia can occur, with multiple-organ involvement.