2. Introduction
There are five approaches to the diagnosis of viral
diseases by the use of clinical specimens:
1. Identification of the virus in cell culture
2. Microscopic identification directly in the specimen
3. Serologic procedures to detect a rise in antibody titer
4. Detection of viral antigens in blood or body fluids
5. Detection of viral nucleic acids in blood or the
patient’s cells
3. Cell Culture
Virus can not grow in cell free media and requires cell
culture for growth
Virus growth in cell culture frequently produces a
characteristic cytopathic effect (CPE)
CPE is the change like size, shape and syncytia of virus
infected cells, usually manifest dying or dead condition
of virus infected cells
If the virus does not produce a CPE, its presence can be
detected by several other technique like
hemadsoption, interference etc
4. Cont...
Hemadsorption: attachment of erythrocytes to the
surface of virus-infected cells). This technique is
limited to viruses with a hemagglutinin protein on
their envelope, such as mumps, parainfluenza, and
influenza viruses.
Interference with the formation of a CPE by a second
virus. For example, rubella virus, which does not cause
a CPE, can be detected by interference with the
formation of a CPE by certain enteroviruses, such as
echovirus or Coxsackie virus.
Decrease in Acid Production by infected dying cells
5. Cont...
A definitive identification of the virus grown in cell
culture is made by using known antibody in one of
several tests like
Complement fixation
Hemagglutination inhibition
Neutralization
Fluorescent antibody
Radioimmunoassay
Enzyme-linked Immunosorbent assay (ELISA)
Immunoelectron microscopy
6. 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
1. Light microscopy reveal inclusion bodies
2. UV Microscopy used for flourescent antibody staining
3. Electron Microscopy detects virus particles
7. Serologic Procedures
Serology is the scientific study of serum and other body
fluids.
In practice, the term usually refers to the diagnostic
identification of antibodies in the serum
A rise in the titer of antibody to the virus can be used to
diagnose current infection
The patient’s serum has converted from antibody-negative
to antibody-positive is called seroconversion
The presence of IgM can be used to diagnose current
infection
The presence of IgG cannot be used to diagnose current
infection
An antibody titer that is fourfold or greater in the
convalescent serum sample compared with the acute
sample can be used to make a diagnosis
8. Detection of Viral Antigens
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.
9. 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.
If only small amounts of viral nucleic acids are present
in the patient, the polymerase chain reaction can be
used to amplify the viral nucleic acids.
Assays for the RNA of HIV and hepatitis C virus and
the DNA of hepatitis B virus in the patient’s blood
(viral load) are commonly used to monitor the course
of the disease and to evaluate the patient’s prognosis
