The paramyxoviridae viruses.
The paramyxoviridae are very
They are large, enveloped,
with a helical capsule,
and they have a linear, single-stranded,
negative-sense RNA genome.
So again, if you remember
anything about this particular
family of virus,
this is a negative-sense RNA virus,
which means that it must carry,
and it does, its own
RNA-dependent RNA polymerase, the RDRP.
You can see in a transmission electron
micrograph in front of you a
picture of one of the paramyxoviruses, and
it's a very large shaped organism.
There are many medically relevant species
in this family, the paramyxoviridae.
Measles virus, mumps virus, the human
parainfluenza virus, cause of croup.
Respiratory syncytial virus, a huge cause
of bronchiolitis in children,
and then the human metapneumovirus, which is
very much -- almost like a combination of
parainfluenza and respiratory
So, a whole bunch of nasties in
this particular family.
So, all of these viruses, the paramyxoviruses,
have the same pathogenesis.
. So they start with a two-step
The first is attaching to their
a fusion protein, the F protein.
And then there's a secondary fusion
with the envelope of the virus
and the cell membrane of the target cell.
And then the capsid itself is
released into the cell.
Now, importantly, 1 cell can be
be infected with or attacked by
multiple of the paramyxoviruses,
giving it the appearance of
a multinucleated cell.
It's just a whole bunch of viral
capsids inside that cell.
As that primary infection occurs, it's
occurring with the epithelial cells of the
upper respiratory tract.
Kind of makes sense because all
these have a respiratory
and so one breathes in the virus, they
attack the upper respiratory tract,
and one gets these viruses bound to
the airway respiratory epithelium.
In the case of measles and mumps,
the first 2 that we'll talk about,
there is then a secondary viremic spread,
which accounts for the systemic
manifestations of those 2 viruses.
In the case of the parainfluenza, RSV,
and human metapneumovirus,
there is not a viremia.
So they account for primarily
Here, we see an image of a
This is an epithelial cell with the green
arrow to make sure you can't miss it.
But it has multiple capsids,
multiple virion capsids
inserted into its cytoplasm.
Now, importantly, this whole
family of cells are
both sensitive to and inducers
So they almost self-stimulate to
create even further impact
through the effects of interferon.