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1. Laboratory diagnosis of viral infections
❖1-Sampling
❖2-Virus isolation
❖3-Nucleic acid based methods
❖Polymerase chain reaction
❖Sequencing
❖4-Microscopy based methods
❖Immunofluorescence or immunoperoxidase
❖Electron microscopy
❖5-Host antibody detection
❖6-Hemagglutination assay
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2. diagnoses of viral diseases
❖ 1-Sampling
❖ 2-Virus isolation
❖ 3-Nucleic acid based methods
❖ Sequencing
4-Microscopy based
methods
❖ 5-Host antibody
detection

3. sampling
temperatures (usually 4 °C) to preserve
the virus and prevent bacterial or
fungal growth. Sometimes multiple
sites may also be sampled.
Types of samples include the following:

4. A wide variety of samples can
be used for virological testing.
The type of sample sent to the
laboratory often depends on the
type of viral infection being
diagnosed
and
the test required.

5. sample
Proper sampling technique is
essential to avoid potential pre-
analytical errors.
For example
and stored at appropriate
different types of samples must
be collected in appropriate tubes
to maintain
the integrity of the sample

6. stored at appropriate
temperatures (usually
4 °C) to preserve the
virus and prevent
bacterial or fungal
growth.

7. Types of samples include the following
1. Nasopharyngeal swab
2. Blood
3. Skin
4. Sputum, gargles and bronchial
washings
5. Urine
6. Semen
7. Faeces
8. Cerebrospinal fluid
9. Tissues (biopsies or post-mortem)

8. Viruses are often isolated from the initial
patient sample.
This allows the virus sample to be grown
into larger quantities and allows a larger
number of tests to be run on them. This is
particularly important for samples that
contain new or rare viruses for which
diagnostic tests are not yet developed

9. Many viruses can be grown in cell
culture in the lab.
To do this, the virus sample is mixed with
cells, a process called adsorption, after
which the cells become infected and
produce more copies of the virus.[

10. Although different viruses often only grow
in certain types of cells, there are cells that
support the growth of a large variety of
viruses and are a good starting point, for
example, the African monkey kidney cell
line (Vero cells), human lung fibroblasts
(MRC-5), and human epidermoid
carcinoma cells (HEp-2). One means of
determining whether the cells are
successfully
replicating the virus is to check for a
change in cell morphology or for the
presence of cell death using a microscope.

11. Other viruses may require alternative
methods for growth such as the inoculation
of embryonated chicken eggs (e.g. avian
influenza viruses[4]) or the intracranial
inoculation of virus using newborn mice
(e.g. lyssaviruses[5

12. Nucleic acid based methods
Molecular techniques are the most specific
and sensitive diagnostic tests
They are capable of detecting either the
whole viral genome or parts of the viral
genome.
In the past nucleic acid tests have mainly
been used as a secondary test to confirm
positive serological results However, as
they become cheaper and more
automated, they are increasingly becoming
the primary tool for diagnostics

13. Polymerase chain reaction[
Detection of viral RNA and DNA genomes
can be performed using polymerase chain
reaction. This technique makes many
copies of the virus genome using virus-
specific probes. Variations of PCR such as
nested reverse transcriptase PCR and real
time PCR can also be used to determine
viral loads in patient serum. This is often
used to monitor treatment success
in HIV cases.

14. Sequencing[
Main article: Whole genome sequencing
Sequencing is the only diagnostic method
that will provide the full sequence of a virus
genome. Hence, it provides the most
information about very small differences
between two viruses that would look the
same using other diagnostic tests..

15. Currently it is only used when this depth of
information is required. For example,
sequencing is useful when specific
mutations in the patient are tested for in
order to determine antiviral therapy and
susceptibility to infection. However, as the
tests are getting cheaper, faster and more
automated, sequencing will likely become
the primary diagnostic tool in the future

16. Host antibody detection person who has
recently been infected by a virus will
produce antibodies in their bloodstream
that specifically recognize that virus. This is
called humoral immunity. Two types of
antibodies are important. The first
called IgM is highly effective at neutralizing
viruses but is only produced by the cells of
the immune system for a few weeks. The
second, called, IgG is produced
indefinitely.

17. Therefore, the presence of IgM in the blood
of the host is used to test for acute
infection, whereas IgG indicates an
infection sometime in the past Both types
of antibodies are measured when tests
for immunity are carried out
Antibody testing has become widely
available. It can be done for individual
viruses (e.g. using an ELISA assay) but
automated panels that can screen for
many viruses at once are becoming
increasingly common.

18. The hemagglutination
assay or hemagglutination assay (HA)
and the hemagglutination inhibition
assay (HI or HAI) were developed in
1941–42 by American virologist George
Hirst as methods for quantifying the
relative concentration of viruses, bacteria,
or antibodies