HSV infection is characterized by a primary infection, often asymptomatic, after which the virus remains dormant in the dorsal root ganglia of peripheral nerves interrupted in some patients by one or more episodes of recurrent disease. Primary infection usually requires a person without preexisting HSV antibody. However, a person can have antibody against one strain of HSV (from previous infection) and become infected by a different strain (reinfection as opposed to reactivation or recurrence of preexisting disease). Primary infection or reinfection is usually acquired from close contact with an infected person: the mouth in cases of nongenital infection, and sexual intercourse in cases of genital infection. However, transmission can occur through body secretions. Immunocompromised persons are at increased risk of primary HSV infection and reactivation. There are two closely related but distinct types of HSV that share some antigens but not others. Herpes simplex virus type 1 (HSV-1) typically produces nongenital infections of various types such as lesions of the mouth, blisters on the mucous membrane border of the lips (“canker sores,” or “cold sores”), keratitis (corneal ulcers of the eye), focal lesions of the fingers (“Whitlow”), and encephalitis (most frequently involving the temporal lobes of the brain). Occasional immunocompromised patients develop disseminated HSV-1 disease. At one time about 90% of the population was found to have antibodies against HSV-1, but more recently this incidence is said to have fallen to about 25%-50%. About 20%-45% of patients with HSV-1 oral lesions eventually develop recurrence. Herpes simplex virus type 2 (HSV-2) produces blistering lesions (vesicles) on the genitalia of males and females and is considered a venereal disease. Reports indicate that HSV-2 causes 20%-50% of genital ulcerations in U.S. sexually transmitted disease clinics. About 5%-15% of patients with genital herpes have HSV-1 isolated rather than HSV-2, and one report indicates that up to 20% of labial or facial lesions are due to HSV-2 rather than HSV-1. About 85% of persons with HSV-2 with genital lesions have recurrences.

In primary HSV-2 genital infection that is symptomatic, the incubation period is about 5-7 days (range, 1-45 days). About one half of the patients (range, 39%-68%) develop systemic symptoms (e.g., fever, malaise, myalgia, and headache), including a subset of about 25% (range, 13%-36%) of all patients who experience a mild self-limited episode of aseptic meningitis (which has a marked difference in severity and prognosis from the severe brain infection of HSV-1). Extragenital lesions on skin or mucous membranes occur in about 25% of patients (range, 10%-30%), most often in the general area of the groin. A few patients develop lesions on one or more fingers, and herpes ocular keratitis sometimes occurs. About 20% are reported to show evidence of pharyngeal involvement, and about 50% have urethral involvement. Herpes simplex virus can be cultured from the cervix in 80%-90% of female patients. About 80% of all patients develop tender inguinal adenopathy in the second or third week.

Recurrent infection differs considerably from primary infection. Only about 5%-10% of patients experience systemic symptoms. Extragenital lesions appear in about 5%. Cervical culture is reported to detect HSV in less than 15%.

Neonatal HSV infection is usually due to HSV-2 associated with active maternal HSV-2 genital infection and is usually (but not always) acquired during birth rather than by transmission through the placenta. About 1% of pregnant women are estimated to have either overt or nonapparent HSV-2 infection. However, asymptomatic cervical or vulvar infection has itself been reported in about 1% (range, 0.5%-8.0%) of women. In genital HSV-2 infection during pregnancy only about 40% of infected women have typical lesions, and about 40% do not have visible lesions. It is estimated that if primary maternal HSV infection is present at delivery, there is a 40%-60% chance of symptomatic neonatal HSV-2 infection. If this occurs, there is serious or even fatal disease in about 50% of those infants. Delivery-infected infants do not develop symptoms until several days to 4 weeks after delivery. Symptoms may suggest sepsis or meningitis. If recurrent maternal HSV is present, there is only about a 5%-8% chance of infant infection. It is also reported that 70%-80% of neonatally infected infants are born to mothers who are asymptomatic at the time of delivery.

Diagnosis of herpes simplex infection culture.

Culture is still considered the gold standard HSV diagnosis. Material for culture must be inoculated into special transport media. Although some authorities advocate freezing the specimen, others report that refrigerator temperature is better for virus in transport media. Culture sensitivity depends on several factors. Some types of cells used for culture give better results than others. Specimens taken from vesicular lesions are considerably (50%-100%) more sensitive than material taken from ulcerative lesions, which, in turn, provide better results than crusted lesions. The earlier a lesion is cultured after it appears, the more likely it will yield a positive result (in one study, culture was positive in 70% of lesions less than 24 hours old, 50% in those 24-48 hours old, and 35% in those over 5 days old). A lesion from a primary infection is more likely to be positive than a lesion due to reinfection or recurrence. When urine or other secretions are cultured, the results from patients with primary infections are much more likely to be positive, since they shed virus much longer than patients with reinfection or recurrent disease. Culture in asymptomatic patients is much less likely to be positive than in patients with lesions. In addition to problems with sensitivity, specimens (in most hospitals) must be sent to a reference laboratory.

Antigen detection. Several methods are available to detect HSV antigen; most differentiate between HSV-1 and HSV-2 or claim to be specific for one or the other. Most have the advantage of same-day or overnight results. Some depend on abbreviated culture followed by use of specific antibody to HSV. Others (such as fluorescent immunoassay or latex agglutination) employ specific antibody on material from clinical specimens. To date, all methods have failed to consistently detect 95% or more patients who have positive results by standard culture and, in general, independent evaluations have not consistently upheld manufacturer’s claims. Some have achieved sensitivity in the 85%-95% range compared to culture; others have not. In general, whether the lesion is from primary or recurrent infection, the type of lesion and the number of days after the lesion appears before the specimen was obtained affects methods that detect HSV antigen similarly to culture. Sensitivity of direct antigen methods tends to be better in material from mucocutaneous vesicles than from genital lesions. Also, there have been problems in cross-reaction between HSV-1 and HSV-2, especially in fluorescent antibody methods. Some nucleic acid probe methods with PCR amplification have been reported to be equal to or better than culture in tissue or CSF.

Direct smear methods. The most rapid diagnosis is made through stained smears from scrapings obtained from a lesion. A sterile scalpel blade is used to unroof a vesicle and material from gentle scraping of the base of the lesion is smeared gently on a slide. Giemsa, Wright’s, or Papanicolaou stains can be used. For Giemsa or Wright’s stain, the smear is air-dried or fixed in methanol. For Papanicolaou, the smear is immediately fixed in cytology fixative. The slide preparation is sometimes called a Tzanck test. The technologist looks for multi-nucleated epithelial cells with enlarged atypical nuclei. The same findings are seen in varicella-zoster lesions. Pap stain also can show intranuclear inclusions. Sensitivity of the Tzanck test is reported to be 30%-91%, with average sensitivity probably about 45%-50%. It is probably less with persons who are inexperienced in obtaining specimens and interpreting the smears. Sensitivity is higher from vesicle scrapings than from other specimens. Fluorescent antibody tests have been applied to the smears, which increases positive results to about two thirds of cases.

Serologic tests for antibody. Most current methods are ELISA or fluorescent immunoassay plus a few LA kits. Antibody detection has also been somewhat disappointing. Acute and convalescent specimens must be obtained 2 weeks apart. A fourfold rise in titer is needed to prove recent onset of infection; this is most likely to be found in HSV-2 disease and during the time of primary infection (60%-70% of cases). Only about 5% of patients with recurrent HSV demonstrate a fourfold rise in titer. There may also be problems with interpretation due to the high rate of positive results in the general population and because of cross-reaction between HSV-1 and HSV-2 antibodies.

Other tests. In culture-proved HSV-1 encephalitis, one study reported that radionuclide brain scan revealed a focal lesion or lesions in the temporal lobe in 50% of cases, computerized tomography scan displayed some type of abnormality in 59%, and electroencephalogram (EEG) was abnormal in 81%. However, these procedures or their results cannot prove that the etiology is herpes infection. Spinal fluid tests show elevated CSF protein levels in about 80% of cases, increased WBC count in 97% (with about 75% of all cases between 50 and 500 WBCs/mm3), and normal glucose levels in 95% of cases. Another study found a normal cell count and protein level in 10% of cases on first spinal tap. Increase in WBC count is predominantly lymphocytic, although segmented neutrophils may be present in varying percentage (occasionally substantial) in the early stages. CSF immunofluorescent IgG antibody tests are about 25% sensitive by 10 days after onset of symptoms and about 85% after 15 days. At present, brain biopsy with culture of the specimen is the most accurate method of diagnosis. However, there is controversy about biopsy of such a vital organ. Culture of brain biopsy specimens is said to detect up to 95% of patients with HSV–1 encephalitis. Microscopic examination of the biopsy specimens can demonstrate encephalitis in about 85% of cases, but detects the intranuclear inclusions necessary to diagnosis HSV in only about 50% of cases. Use of immunofluorescent staining methods increases diagnosis to about 70%. Nucleic acid probe with PCR amplification was reported to detect over 95% of patients with HSV encephalitis testing CSF. However, homemade reagents were used. Clinical assessment alone is not sufficiently accurate: in one series of patients who underwent brain biopsy for suspected herpes, about 45% did not disclose herpes and about 10% were found to have treatable diseases other than herpes. CSF culture was positive in only about 5% of patients whose brain biopsy results were culture positive. In one large series, serologic tests suggested that 30% of patients had primary HSV infection and 70% had recurrent infection.