Laboratory Diagnosis of Viruses | Microbiology Lectures 2019 | Medical Student Learning

Introduction to Diagnostic Methods
In this lecture educator explains about Laboratory Diagnosis of Viruses. Diagnostic virology is rapidly moving into the mainstream of clinical medicine as a result of the convergence of several independent developments. Historically, diagnostic virology has had to justify its use.

Identification in cell culture: The growth of viruses requires cell cultures because viruses replicate only in living cells, not on cell-free media the way most bacteria can. Because many viruses are inactivated at room temperature, it is important to inoculate the specimen into the cell culture as so++on as possible; brief transport or storage at 4°C is acceptable.

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Classical Detection Techniques
A definitive identification of the virus grown in cell culture is made by using known antibody in one of several tests. Complement fixation, hemagglutination inhibition, and neutralization of the CPE are the most frequently used tests. Other procedures such as fluorescent antibody, radioimmunoassay, enzyme-linked immunosorbent assay (ELISA), and immunoelectron microscopy are also used in special instances.

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Newer Detection Techniques
Radioimmunoassay: If the virus and the antibody are homologous, there is less antibody remaining to bind to the known radio labelled virus.

ELISA: In the ELISA test to identify a virus, known antibody is bound to a surface. If the virus is present in the patient’s specimen, it will bind to the antibody. A sample of the antibody linked to an enzyme is added, which will attach to the bound virus. The substrate of the enzyme is added, and the amount of the bound enzyme is determined.

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Microscopic and Serologic Methods
Microscopic identification: Viruses can be detected and identified by direct microscopic examination of clinical specimens such as biopsy material or skin lesions. Three different procedures can be used.

Light microscopy can reveal characteristic inclusion bodies or multinucleated giant cells. The Tzanck smear, which shows herpesvirus-induced multinucleated giant cells in vesicular skin lesions, is a good example.
UV microscopy is used for fluorescent antibody staining of the virus in infected cells.

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Detection of Viral Antigens and Nucleic Acids
Detection of p24 antigen: Viral antigens can be detected in the patient’s blood or body fluids by various tests, but most often by an ELISA. Tests for the p24 antigen of human immunodeficiency virus (HIV) and the surface antigen of hepatitis B virus are common examples of this approach.

Detection of viral nucleic acid: Viral nucleic acids (i.e., either the viral genome or viral mRNA) can be detected in the patient’s blood or tissues with complementary DNA or RNA (cDNA or cRNA) as a probe.

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Duration of medical lecture: 01:16:13
Release date: December 2017

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