ORTHOMYXOVIRUSES AND
PARAMYXOVIRUSES
Lets start by listing the similarities and differences
between orthomyxoviruses and paramyxoviruses, then
I will describe orthomyxoviruses only in detail (not
paramyxoviruses):
The similarities:
1. Both have negative stranded RNA
2. Both families are have lipid containing envelope
3. Both families have HA and NA glycoproteins ( but there
are exceptions, I will mention them later)
4. Both have a helical symmetry capsid
The differences:
1. Orthomyxoviruses have segmented negative stranded RNA
(7-8) segments, whereas paramyxoviruses are not
segmented.
2. Orthomyxoviruses replicate in the nucleus (they are the only
RNA viruses that replicate in the nucleus in addition to
retroviruses), whereas paramyxoviruses replicate in the
cytoplasm
3. Orthomyxoviruses include influenza A,B,C, whereas
paramyxoviruses include parainfluenza, respiratory
syncytial
virus, metapneumovirus, mumps and measles.
4. Orthomyxoviruses have HA and NA glycoproteins on 2
different spikes, whereas paramyxoviruses have HA and NA
as a part of the same glycoprotein spike, not 2 different
spikes.
, 5. Orthomyxoviruses doesn’t have a fusion (F) protein that
causes the infected host cells to fuse together into
multinucleated giant cells, whereas paramyxoviruses have
this protein.
Exceptions:
1. The respiratory syncytial virus doesn’t have HA nor NA
glycoproteins (so, it is a virulence factor)
2. There is HA, but there is no NA on measles envelope
3. Metapneumovirus has integrin alpha V-beta
receptor allows infection of respiratory tract epithelial cells.
Orthomyxoviruses (influenza):
Percentage: approximately 20% of the entire world
population gets infected with the influenza virus each year!
Structure: they are spherical virions. At the virion
center lie 8 segments of negative stranded RNA put
together with a protein (nucleocapsid protein) into a helical
symmetry capsid. Surrounding the nucleocapsid lies an
outer membrane studded with long glycoprotein spikes.
There are 2 distinct types of
glycoprotein: 1. Hemagglutinin activity: hemagglutinin can
attach to host sialic acid receptors. Sialic acid receptors
are present on the surface of erythrocytes, so viruses with
HA glycoproteins cause heme-agglutination when mixed
with red blood cells. In addition to erythrocytes, sialic acid
receptors also exist on upper respiratory tract cell
membranes, when HA binds to these receptors, it activates
the fusion of the host cell membrane with the virion
membrane. So, HA is needed for adsorption. Antibodies
against HA will block this binding and prevent
infection. 2. Neuraminidase: Neuraminic acid is an
PARAMYXOVIRUSES
Lets start by listing the similarities and differences
between orthomyxoviruses and paramyxoviruses, then
I will describe orthomyxoviruses only in detail (not
paramyxoviruses):
The similarities:
1. Both have negative stranded RNA
2. Both families are have lipid containing envelope
3. Both families have HA and NA glycoproteins ( but there
are exceptions, I will mention them later)
4. Both have a helical symmetry capsid
The differences:
1. Orthomyxoviruses have segmented negative stranded RNA
(7-8) segments, whereas paramyxoviruses are not
segmented.
2. Orthomyxoviruses replicate in the nucleus (they are the only
RNA viruses that replicate in the nucleus in addition to
retroviruses), whereas paramyxoviruses replicate in the
cytoplasm
3. Orthomyxoviruses include influenza A,B,C, whereas
paramyxoviruses include parainfluenza, respiratory
syncytial
virus, metapneumovirus, mumps and measles.
4. Orthomyxoviruses have HA and NA glycoproteins on 2
different spikes, whereas paramyxoviruses have HA and NA
as a part of the same glycoprotein spike, not 2 different
spikes.
, 5. Orthomyxoviruses doesn’t have a fusion (F) protein that
causes the infected host cells to fuse together into
multinucleated giant cells, whereas paramyxoviruses have
this protein.
Exceptions:
1. The respiratory syncytial virus doesn’t have HA nor NA
glycoproteins (so, it is a virulence factor)
2. There is HA, but there is no NA on measles envelope
3. Metapneumovirus has integrin alpha V-beta
receptor allows infection of respiratory tract epithelial cells.
Orthomyxoviruses (influenza):
Percentage: approximately 20% of the entire world
population gets infected with the influenza virus each year!
Structure: they are spherical virions. At the virion
center lie 8 segments of negative stranded RNA put
together with a protein (nucleocapsid protein) into a helical
symmetry capsid. Surrounding the nucleocapsid lies an
outer membrane studded with long glycoprotein spikes.
There are 2 distinct types of
glycoprotein: 1. Hemagglutinin activity: hemagglutinin can
attach to host sialic acid receptors. Sialic acid receptors
are present on the surface of erythrocytes, so viruses with
HA glycoproteins cause heme-agglutination when mixed
with red blood cells. In addition to erythrocytes, sialic acid
receptors also exist on upper respiratory tract cell
membranes, when HA binds to these receptors, it activates
the fusion of the host cell membrane with the virion
membrane. So, HA is needed for adsorption. Antibodies
against HA will block this binding and prevent
infection. 2. Neuraminidase: Neuraminic acid is an
