Page 277 - Review of Medical Microbiology and Immunology ( PDFDrive )

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Laboratory Diagnosis

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CHAPTER C ONTENT S
Introduction
Serologic Procedures
Identification in Cell Culture
Detection of Viral Antigens
Complement Fixation
Detection of Viral Nucleic Acids
Hemagglutination Inhibition
Pearls
Neutralization
Fluorescent Antibody Assay
Practice Questions: USMLE & Course Examinations
Radioimmunoassay
Enzyme-Linked Immunosorbent Assay Self-Assessment Questions
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mebooksfree.com mebooksfree.com mebooksfree.com detected by several other techniques: mebooksfree.com mebooksfree.com
Immunoelectron Microscopy

INTRODUCTION
If the virus does not produce a CPE, its presence can be
There are five approaches to the diagnosis of viral dis-
(1) Hemadsorption (i.e., attachment of erythrocytes to
eases by the use of clinical specimens: (1) identification
the surface of virus-infected cells). This technique is lim-
of the virus in cell culture, (2) microscopic identification
directly in the specimen, (3) serologic procedures to
lope, such as mumps, parainfluenza, and influenza viruses.
detect a rise in antibody titer or the presence of IgM anti-
(2) Interference with the formation of a CPE by a sec-
body, (4) detection of viral antigens in blood or body
ond virus. For example, rubella virus, which does not cause
fluids, and (5) detection of viral nucleic acids in blood or ited to viruses with a hemagglutinin protein on their enve-
a CPE, can be detected by interference with the formation
mebooksfree.com mebooksfree.com mebooksfree.com cells. This can be detected visually by a color change in the mebooksfree.com
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the patient’s cells.
of a CPE by certain enteroviruses, such as echovirus or
Coxsackie virus.
IDENTIFICATION IN CELL CULTURE
(3) A decrease in acid production by infected, dying
The growth of viruses requires cell cultures because viruses
phenol red (a pH indicator) in the culture medium. The
replicate only in living cells, not on cell-free media the way
indicator remains red (alkaline) in the presence of virus-
most bacteria can. Because many viruses are inactivated at
infected cells but turns yellow in the presence of metabo-
room temperature, it is important to inoculate the speci-
lizing normal cells as a result of the acid produced. This
men into the cell culture as soon as possible; brief transport
technique can be used to detect certain enteroviruses.
or storage at 4°C is acceptable.
Virus growth in cell culture frequently produces a char-
A definitive identification of the virus grown in cell
acteristic cytopathic effect (CPE) that can provide a pre-
tests. Complement fixation, hemagglutination inhibition,
sumptive identification. CPE is a change in the appearance culture is made by using known antibody in one of several
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mebooksfree.com mebooksfree.com mebooksfree.com (ELISA), and immunoelectron microscopy are also used in mebooksfree.com
of the virus-infected cells. This change can be in such fea-
and neutralization of the CPE are the most frequently used
tures as size, shape, and the fusion of cells to form multi-
tests. Other procedures such as fluorescent antibody, radio-
nucleated giant cells (syncytia). CPE is usually a
immunoassay, enzyme-linked immunosorbent assay
manifestation of virus-infected cells that are dying or dead.
special instances. A brief description of these tests follows.
The time taken for the CPE to appear and the type of cell in
They are described in more detail in the section on
which the virus produces the CPE are important clues in
immunology.
the presumptive identification.
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