Herpes simplex virus (HSV)

HSV-1 and HSV-2 belong to the family of Herpes viruses and are able to establish latent infection in dorsal root ganglia.

HSV is transmitted from infected to susceptible individuals during close personal contact. Asymptomatic infection is common.

Primary HSV-1 infection is usually oral and manifestations include fever, sore throat, ulcerative and vesicular lesions, gingivostomatitis and local lymphadenopthy. The lesions can be painful and last for 10–14 days. Vesicles are usually grouped in a single anatomic site; however, autoinoculation of distant locations, for example, skin, can occur. Recurrent orolabial lesions are rarely associated with systemic symptoms; there are a small number of localised vesicles and crusting begins within 72–96 hours.

HSV-1 can also cause keratoconjunctivitis and sporadic cases of encephalitis and has an association with erythema multiforme.

Genital infections can be asymptomatic, mild or severe, with painful genital ulcers, dysuria, fever, tender local inguinal lymphadenopathy and headache. Complications include meningitis and urinary retention. Proctitis may occur in men who have sex with men.

The wide variation in clinical manifestations of genital HSV depends upon whether the infection is:

New diagnoses of genital herpes are equally likely to be caused by HSV-1 or HSV-2.

Non-primary first episode genital infection is associated with fewer lesions and fewer systemic symptoms than primary infection, presumably because antibodies against one HSV type offer some protection against the other.

Clinical recurrences of genital HSV are common but are typically less severe than primary or non-primary infections. Recurrences of genital HSV-1 infection are less common than when a patient acquires HSV-2 infection.

Subclinical shedding of HSV-1 or HSV-2 is common in both immunocompetent and immunocompromised patients.

HSV PCR is now the test of choice for diagnosis of acute herpes simplex virus infections.

HSV-1 and HSV-2 serology is not recommended to confirm the aetiology of a vesicular rash, as PCR is the method of choice for this indication. Antibodies may take weeks to develop after infection. Serology is used during pregnancy to distinguish primary from non-primary infection and from recurrent infection.

The greatest risk of transmission to the newborn occurs with a primary genital infection in the third trimester. If a woman develops genital lesions suggestive of HSV during pregnancy, viral swabs for PCR should be collected to confirm HSV infection and type. Serology should also be performed to distinguish primary infection vs. recurrent infection vs. new acquisition of the other HSV type in the genital area (HSV antibody positive to the type other than that isolated from genital culture).

Managment of primary HSV infection in pregnancy is complex and specialist advice should be sought.