Orthomyxo-Comparitive morphology,Replication,cultivation,epidemiology,pathogenesis& Diagnosis

1. Orthomyxo Virus
Dr Sumitha J
Associate Professor
JBAS College for Women,Teynampet,Chennai-18

2. Morphology
• Orthomyxoviruses are enveloped viruses that have a helical nucleocapsid. The virion
(virus particle) is pleomorphic, meaning that it can have a variety of shapes, but is
typically spherical or filamentous.
• The diameter of the virion is 80 to 120 nanometers (nm).
• The envelope is made up of a lipid bilayer that is derived from the host cell
membrane.
• The spikes on the surface of the envelope are made up of two glycoproteins:
hemagglutinin (HA) and neuraminidase (NA).

3. Morphology
• HA: The HA glycoprotein is responsible for attaching the virus to the host cell. It does
this by binding to sialic acid molecules on the surface of the cell.
• NA: The NA glycoprotein is responsible for releasing the virus from the host cell. It
does this by cleaving sialic acid molecules from the cell surface.
• Nucleocapsid: The nucleocapsid is a helical structure that is made up of nucleoprotein
(NP) molecules. The NP molecules are arranged in a spiral fashion around the viral
RNA.
• RNA genome: The RNA genome of orthomyxoviruses is single-stranded and
negative-sense. This means that the RNA is complementary to the mRNA that is used
to make proteins.

6. Morphology
• Paramyxoviruses have two main types of surface proteins: hemagglutinin (HA) and
neuraminidase (NA).
• Hemagglutinin (HA): The HA protein is responsible for attaching the virus to the
surface of a cell. It does this by binding to sialic acid, a type of sugar that is found on
the surface of cells.
• Neuraminidase (NA): The NA protein is responsible for releasing the virus from the
cell. It does this by cleaving sialic acid molecules from the cell surface

7. Cultivation
• Cell culture: This is the most common method for cultivating orthomyxoviruses. Cells are
grown in a laboratory dish and the virus is added to the culture. The virus will then infect the
cells and replicate. The CPE of the virus can be observed and the virus can be isolated and
purified.
• Animal models: Orthomyxoviruses can also be cultivated in animal models, such as chickens,
ferrets, and mice. The virus is injected into the animal and the infection is monitored. This
method is useful for studying the pathogenesis of the virus and for developing new treatments.
• In ovo: This method involves injecting the virus into the egg of a chicken. The virus will then
infect the embryo and replicate. The embryo can then be harvested and the virus can be
isolated and purified. This method is useful for studying the replication of the virus and for
developing new vaccines.

8. Cultivation
• The cultivation of orthomyxoviruses can be a challenging process, as the viruses are sensitive to
changes in temperature and pH. The cells used for cultivation must also be susceptible to the
virus.
• The cell culture method is the most common method for cultivating orthomyxoviruses. The cells
that are most commonly used for cultivating influenzaviruses are Madin-Darby canine kidney
(MDCK) cells and human embryonic kidney (HEK) cells.
• The animal models that are most commonly used for cultivating orthomyxoviruses are chickens,
ferrets, and mice. Chickens are the most susceptible animals to influenzaviruses. Ferrets are
also susceptible to influenzaviruses, and they are often used to study the pathogenesis of the
virus. Mice are less susceptible to influenzaviruses, but they are useful for studying the immune
response to the virus.
• The in ovo method is not as commonly used as the cell culture method or the animal model
method. However, it can be useful for studying the replication of the virus and for developing new
vaccines.

9. Replication
• The virus attaches to the surface of a cell using its HA protein: The HA protein is a
surface protein that helps the virus attach to the cell. It is also responsible for the
formation of syncytia.
• The viral RNA is transcribed into DNA by a viral enzyme called reverse transcriptase.
• The DNA is then integrated into the host cell genome.
• The virus replicates and produces new virions.
• The new virions are released from the cell and can infect other cells.The NA protein is
a surface protein that helps the virus release from the cell. It is also responsible for
the cleavage of sialic acid, a type of sugar that is found on the surface of cells.The
virus fuses with the cell membrane and releases its genetic material into the cell.

10. Replication
The replication of orthomyxoviruses can be divided into two phases: the transcription
phase and the replication phase.
•Transcription phase: In the transcription phase, the viral RNA is
transcribed into DNA by reverse transcriptase. The DNA is then
integrated into the host cell genome.
•Replication phase: In the replication phase, the virus replicates
and produces new virions. The new virions are released from
the cell and can infect other cells.

11. Replication
The replication of orthomyxoviruses can be divided into two phases: the transcription
phase and the replication phase.
•Transcription phase: In the transcription phase, the viral RNA is
transcribed into DNA by reverse transcriptase. The DNA is then
integrated into the host cell genome.
•Replication phase: In the replication phase, the virus replicates
and produces new virions. The new virions are released from
the cell and can infect other cells.