The Caliciviridae are very small,
icosahedral capsids, such as you see on
the electron micrograph in front of you.
They have a linear, single-stranded,
positive-sense RNA genome,
which, because it is positive sense, can
function as a messenger RNA.
There are only a couple medically
in this genus.
However, they are quite important.
One is the hepatitis E virus,
which, as you see there, is the
It's very similar to the Caliciviridae,
it is discussed in this family.
And then the Norwalk virus,
which previously may have been called
the Norwalk agent,
or Norwalk-associated virus.
Infection, and let's start with
virus first because it is perhaps the
Infection with Norwalk virus starts as a
primary exposure to the virus,
fecal, oral, many times.
And then entrance, eventually, to
the small intestine
where the virus attaches to the
of the intestine, and it is those cells
that initially have a function affected
by the lysis of the host cell.
As that happens, those cells lose their
ability to absorb
water nutrients, which allows
for a malabsorption diarrhea to develop.
However, the principal component or
of Norwalk virus are coming from its
effect of delaying gastric emptying,
and it is that specific issue
which creates hyperemesis --
and we're talking
explosive hyperemesis because the stomach
is unable to empty,
and that is what drives a lot of the
outbreaks of Norwalk virus.
The picture you see in front of you is
of a cruise ship.
And this should suggest to you or
help you remember
that most of the large outbreaks
virus infection have all occurred on
purulent material seen in a cruise ship.
Incubation period, 24-60 hours,
so just within the perfect time
of a cruise.
Transmission is via the fecal-oral route.
However, this is one of the times
when the emesis, the vomiting, is so
explosive that it
aerosolizes the vomitus.
And so, even if one is trying to wash
on a cruise ship, one may be
walking through a
cloud of virus, a cloud of Norwalk virus
and get infected that way.
This is not to bash the cruise ship
They do a wonderful job of trying to
minimize this of requiring
onboard hygiene, but yet, this is
still a very prominent
mechanism of being exposed to
The clinical manifestations.
The watery diarrhea because it is a
due to poisoning or lysis of the brush
but then the very prominent nausea
Sometimes, there's low grade fevers,
but the whole process thankfully,
So, incubation period, 12-60 hours.
Total length of symptoms, 12-60 hours,
but that's just enough time to get
The Hepatitis E virus, then, is
best discussed in combination or
to the other hepatitis viruses which
are not in the same
In fact, if you look down the columns on
the far left,
hepatitis A virus, and the far right,
hepatitis E virus, you will note that
these are very similar.
In fact, the hepatitis, the
caused by hepatitis E
is very similar to that caused in
Both are transmitted in a fecal-
Both have a very short incubation period.
Both are mostly asymptomatic,
but when they do develop acute disease,
it's quite fulminant.
Hepatitis A can cause acute disease
Hepatitis E is especially fulminant
and even tragic
in women who are pregnant,
in part, due to their immune
and in part, due to increased volume of
delivery for the hepatitis virus.
The mortality rate in hepatitis
A, very low.
Almost all people recover, unless they have
a specific immunodeficiency.
Unfortunately, as just mentioned,
the mortality or death rate in
is very high in women who are pregnant
because they have a transient
as part of their pregnancy.
There is no carrier safe for either
and there are no other associated
or relevant or even
So, this particular group of viruses is
most notable for
norovirus or Norwalk virus as it is
which is a very pronounced cause of a
vomiting, especially gastroenteritis,
and most especially due to closed
environments such as
a cruise ship, closed meetings, etc.
And then hepatitis E virus,
which doesn't cause vomiting, but
can cause a
icteric or jaundiced hepatitis,
which in most cases resolves
The moral to this story for both viruses,
though, is wash your hands
and don't breath when walking through
a cruise ship.