Herpes Simplex Viral Culture

Normal findings in herpes simplex viral culture ^[1] :

• No virus present
• No herpes simplex virus (HSV) antibodies present 

A cell culture positive for herpes simplex virus (HSV) implies probable active infection. Rarely, clinically insignificant asymptomatic shedding of the virus may be grown in culture.

A negative HSV cell culture result does not rule out HSV infection, particularly if the specimen is from cerebrospinal fluid (CSF) or nonvesicular lesions.

Specimen: General recommendations for viral cultures of the specimen type should be followed in collecting the sample; specimen should be collected in the early phase of infection; intact vesicles should be unroofed for collection of the specimen from fresh and wet mucocutaneous lesions

Blood: Buffy coat; 1-7 mL of blood should be collected in a heparinized (green-top) tube; blood is not considered a good specimen for herpes simplex viral culture

Container: Specimens should be placed in a viral transport medium and transported in wet ice at 4°C

All samples must be sent in a sealed, leak-proof container marked with a biohazard sticker to comply with Occupational Safety and Health Administration (OSHA) safety standards.

Description

Herpes simplex virus (HSV) usually causes vesicular rash of the oropharyngeal area or external genitalia. At times, it may cause severe disseminated infection, including multiorgan involvement (skin, eyes, CNS). In an immunocompromised host, HSV may cause disseminated infections and multiorgan failure. Neonatal infections from vertical transmission may occur.

Cultured eukaryote cells such as human foreskin fibroblasts or vero cell cultures are used to inoculate the specimen. For HSV isolation, either tube or shell vial culture may be used. ^[2] Specimens with heavy viral loads (eg, vesicular lesions) may show the cytopathic effect within 1-2 days.

Immunologic techniques such as staining with tagged monoclonal antibodies should be used to confirm cytopathic effects on cell cultures. In most cases, positive culture results are identified within 48 hours. Negative culture results should be incubated up to a week. Shell vial cultures are normally finalized within 2-3 days. ^[2] HSV-1 or HSV-2 antibody reagents may be used to further isolate HSV, if necessary.

Indications/Applications

Herpes simplex viral culture is indicated for the following:

• Mucocutaneous lesions clinically suggestive of HSV infection

• Encephalitis

• Meningitis

Considerations

The criterion standard for HSV laboratory testing is the cell culture. Collected samples should be layered on a monolayer of cells in test tubes. Cytopathic effect of rounded cells indicates the presence of HSV in the sample. ^[3]

Suppression of cellular immunity results in reactivation, spread, and severe illness in diseases caused by herpes viruses.

HSV-1 causes both primary and recurrent disease in the form of gingivostomatitis, keratoconjunctivitis, encephalitis, herpetic whitlow, herpes labialis, and herpes gladiatorum. Disseminated infections, such as esophagitis and pneumonia, occur in immunocompromised patients.

HSV-2 cause both primary and recurrent disease in the form of genital herpes, neonatal herpes, and aseptic meningitis.

Both HSV-1 and HSV-2 infections are associated with erythema multiforme. The lesions are usually macular or papular and occur symmetrically on the trunk, hands, and feet (target lesions). The rash probably results from an immune-mediated response to the HSV antigens. ^[4]

HSV-2 meningitis is one of the major causes of viral meningitis in adults. It is probably second in importance only to enteroviruses as a cause of viral meningitis, accounting for 5% of total cases. HSV meningitis occurs in about 25%-35% of women and 10%-15% of men at the time of primary episode of genital herpes. Twenty percent of these individuals may develop recurrent attacks of meningitis.

The sensitivity of herpes simplex viral culture using CSF may be low; therefore, molecular diagnostic tests should be used. HSV CSF polymerase chain reaction (PCR) is used to diagnose HSV meningitis, as culture results may be falsely negative in this setting, particularly in patients with recurrent meningitis. ^[5]

Collection of specimens from dried and overcrusted lesions is a common pitfall, and this practice should be avoided.

PCR is the most sensitive method for detection of HSV, particularly in CNS infections. For rapid and specific identification of HSV, an HSV-specific direct fluorescent antibody test using cells from the base of the vesicles or wet ulcers may be used. ^[2]

Genital herpes increases the susceptibility to HIV infection. HIV viral load is increased if the patient is co-infected with HSV. HSV-2 infection is considered to be an opportunistic infection in persons with HIV infection (up to 90% of HIV-infected individuals are co-infected with HSV-2). ^[6]