Clinical Virology– In the Department of Pathology

Viral Immunodiagnostics and Viral Culture

Viral Immunodiagnostics:

Stanford Respiratory Virus Testing Algorithm
Immunodiagnosis
Viral Immunodiagnostic testing involves the identification of viral protein antigens in patient samples using antibody reagents.  The major immunodiagnostic testing done in the laboratory is called direct viral exam or direct fluorescent antibody (DFA) testing.  In this technique, the patient’s primary specimen is processed and stained with specific fluorescently-labeled antibodies.  We perform DFA on skin lesions to detect Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV), as well as on ocular specimens for the identification of HSV and adenovirus.   Perhaps most importantly, DFA is currently our initial screening test for the diagnosis of viral respiratory disease (see algorithm below).  Respiratory samples, including nasopharyngeal swabs and bronchoalveolar lavage (BAL) fluid, are tested by DFA for the presence of eight of the most important viral respiratory pathogens: influenza A, influenza B, respiratory syncytial virus (RSV), adenovirus, parainfluenza viruses 1, 2, and 3, and metapneumovirus (MPV).        

Viral Culture:

While the direct viral exam is relatively rapid, other methods of viral diagnosis, including viral culture and viral nucleic acid amplification testing (see the molecular virology page), are more sensitive.  Viral culture may be particularly useful in cases with a broad viral differential as this technique provides a relatively unbiased approach to the identification of viral pathogens.  Viral culture utilizes a series of primary cell lines (Human Fibroblast, Rhesus Monkey Kidney) and continuous cell lines (A549 Human Lung Carcinoma) selected for their ability to support the replication of a wide variety of clinically relevant viruses.  Specimens are inoculated onto these cell culture monolayers and monitored by light microscopy for cytopathic effect (CPE), the visible cellular changes that occur in response to viral infection. 

Based on the specimen source, the time to CPE, the quality of the CPE, and the cell line(s) showing CPE, a preliminary identification can be made.  The presence of a specific virus is confirmed by immunofluorescent staining using virus-specific, fluorescently-labeled antibodies.  Utilizing viral culture, our laboratory is able to isolate many important pathogenic viruses (including HSV, VZV, cytomegalovirus (CMV), adenovirus, enterovirus, influenza virus, RSV, parainfluenza virus, and rhinovirus) from essentially any source (respiratory, urine, stool, amniotic fluid, tissue, etc.). To expedite the identification of slowly replicating viruses (for example, CMV) we also perform shell vial assays, a modification of traditional viral culture where cells are stained prior to the development of CPE.

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