The reoviridae, viruses.
The reoviridae are medium-sized,
And they are interesting because
they have a segmented,
double-stranded RNA genome,
meaning they have both a positive and a
negative-sense RNA strand in their genome.
he medically relevant reoviridae
rotavirus, quite a common cause
of severe gastroenteritis.
And then, less commonly, the
Colorado tick fever virus.
We can see in the image on the
screen a electron micrograph
of reo -- in fact, in this case,
and they look nice and uniform,
until you get sick from them, in which
case we're very sad indeed.
Pathogenesis of rotavirus, looking
specifically at that one now.
The virions, partially digested,
come through the stomach,
where they are partially acid
susceptible, but still infectious.
nd if they are still infectious, they
can directly penetrate
the intestinal epithelial cells.
There, as they start to replicate, etc.,
they do several things.
One is to secrete a cholera
And again, the virus doesn't secrete that,
but it has a genome, which when transcribed,
creates a protein which
does these functions.
And this cholera toxin protein
allows destruction of the villous absorption,
so the villi at the surface
of that intestinal epithelial cell
and they're unable to absorb
electrons such as sodium, potassium,
which means that water passage
does not occur.
So, one already has a water loss diarrhea,
but at the same time, the
act of the rotavirus
replicating itself also encodes proteins
to increase the proliferation or
of that intestinal epithelial cell.
So the cell, in addition to losing water,
So, rotavirus diarrhea is unusual
because it is both a
secretory diarrhea, and a
You get a sense that maybe there's
a lot of water loss going on.
So, in the diarrhea, when it's occurring,
again, both mechanisms for losing water,
one is also, of course, shedding
tons of virions
because these are the viruses being
produced by those now ruined
intestinal epithelial cells.
That means that rotavirus diarrhea
is incredibly contagious.
Even a small amount can transmit new
disease to somebody else.
Thus, rotavirus diarrhea occurs in
many epidemics every year
throughout, especially closed communities,
daycares, schools, you name it.
It's a very big deal.
The immunity derives, again, from those
partially digested virions in which,
as they're binding to the intestinal
an immunoglobulin A or a mucosal humoral
or antibody reaction is occurring,
and that starts to derive immunity.
However, there are several different
serotypes of rotavirus,
so in fact, one could get rotavirus several
times in one's childhood life.
So, what does the disease look like?
Well, the incubation period
is about 48 hours
Transmission, as you've already
figured out, is fecal-oral.
And the clinical manifestations are
incredibly watery diarrhea,
some vomiting, low-grade fevers
lasting for 4-5 days.
The principal problem, because of
that water loss, then is dehydration;
not gut disruption, but water loss.
As an FYI, because my daughter
also had rotavirus when she was young,
this is an incredibly foul-smelling,
It's just not pleasant to look at at all.
And unfortunately, in changing all those
diapers, you will look at it a lot.
Almost all patients have a self-limited
disease, unless they have
some underlying, you know, deficiency.
Complete recovery is common,
in fact, almost uniform.
some patients, especially those who are
already malnourished or already have
underlying gut distress,
may develop very severe water loss and
they may die from complications
of the rotavirus infection.
Most children however, and
certainly adults if they are
are unlucky enough to acquire
this, will have,
in relative sense, a mild diarrhea,
meaning it only lasts 4-5 days.
Older children also, and adults,
are starting to develop some immunoglobulin
A immunity, and so,
even if they were not vaccinated,
they might actually develop less
severe disease because their enterocytes
are partially protected.
To identify rotavirus, one could look for
viral antigens or the virions in the stool,
and both a serologic assay exists,
as do molecular diagnostics.
Prevention, thankfully, now, comes from
an attenuated rotavirus vaccine,
which when initially created and released,
was associated potentially causally
with an increased risk of intussusception.
Thankfully, a new viral product,
antiviral product has come out, 2 vaccines,
which, so far, have demonstrated
only a mild increase in
potentially related intussusception.
So, prevention, of course, is
the best treatment,
but those patients who still get rotavirus
will require extensive fluid
starting with oral rehydration therapy,
but sometimes, progressing
to intravenous therapy.
So, the second virus in this category,
not to completely ignore it
but is the Colorado tick fever virus.
And as you imagine, given the name,
this is a vector-associated infection.
Incubation period is typically
3-6 days after exposure.
The vector is the Western or
Northwestern wood tick
and thus, you might expose
yourself to this infection
if traveling, hiking, camping, etc.,
in those parts of the States and Canada.
The infection itself is biphasic,
meaning that the initial fever, chills, head=
ache, viral sensitivity, viral syndrome
occurs, there's a period of sometimes
3 to almost 7 days where the
patient is feeling better,
thinking, "Ha ha, phew. Dodged that bullet,"
and then they get sick again
with the same thing.
The full manifestations of
Colorado tick fever are
severe fever with rigors, chills,
bad headaches, which are typically
both frontal and temporal,
light sensitivity, photo sensitivity,
They feel horrible, just generally
lie in bed with malaise,
and patients may develop gastrointestinal
nausea, vomiting, occasionally
some mild diarrhea.
And there occasionally is a rash,
which when noted, is flat,
erythematous, and macular.
It's a very nonspecific rash,
unlike some of the other tick-associated
infections that we've talked about.
The infection itself is self-limited,
so at the end of 2 weeks,
patients will have recovered
from their second
part of the biphasic illness.
So, in thinking about Colorado
tick fever virus,
the key to remember here is that it
occurs in 2 parts as a biphasic
And thinking about the rotavirus, remember,
it's ubiquitous, it'd quite a
and the diarrhea is both osmotic
and secretory together.
To treat rotavirus, prevent it with vaccine,
and give lots of fluids, and watch
out for those diapers.