Now, let's turn to the arboviruses.
And keeping in mind, again, these
through the bite or the saliva
of an insect vector,
which in this case, in the
is almost always mosquitoes.
The mosquitoes participate in a
sylvatic cycle, which
is where the mosquito and a primate host,
not the human,
cycle back and forth a viremia.
With the arbovirus, mosquito takes
a blood meal,
processes it in the salivary gland,
and then gives it back to the
Humans are accidental hosts as occurs in
all vector transmission.
In this case, once the human is bitten
by an infected mosquito,
then the saliva and the arbovirus
transfer into the bloodstream creating
a primary viremia.
Primary infection is then acquired
with delivery into the monocytes,
where initial viral replication
Then, there's a secondary viremia,
so monocytes -- macrophages first,
and then, as those cells are lysed
and release brand new virions, then
secondary viremia occurs.
And then, the arbovirus goes to whatever
its site of action is,
whether that's brain, liver,
blood vessels, skin, etc.
So, the transmission
of the viruses and all the arboviruses,
is due to pretty much 1 of 2
The Aedes mosquito, and that's usually
the Aedes aegypti
or the Aedes albopictus mosquitoes,
these are known as flood plain
meaning that they exist close to
bodies of water,
and mosquito eggs which have been laid
during drought season
can regenerate and create a new
as soon as that dried floodplain
again becomes wet.
o, as you see here, Aedes mosquitoes,
anywhere near water, and they carry
the viruses for dengue and yellow
The Culex mosquito is the larger
and it typically loves forested or
grassy or, sort of,
cool, moist environments.
And many of the encephalitis
for example, the St. Louis encephalitis
come from the Culex mosquito.
Let's look down at the specific diseases
caused by some of these arboviruses.
And we'll start with dengue as it is of
quite significant human concern.
Dengue syndrome or dengue infection is
caused by the dengue virus, makes sense.
And as just mentioned, it is carried by
the Aedes mosquito.
The tropism or the target of the
is primarily vascular endothelium,
and secondarily, macrophages and liver.
Because the target is vascular in nature,
then the severe manifestations of dengue
are almost always hemorrhagic in nature.
However, the very first part of dengue
syndrome, the first infection one gets,
has high fever,
headache, and especially, postseptal
pain, so pain behind the eyes,
as a prominent manifestation.
In addition, there is a nonspecific
and then bone pain for at least 7
days of the total dengue syndrome.
The bone pain is so severe
that in many parts of the world
where dengue is common,
it is referred to as Break Bone Fever
because the bone pain is so -- people swear
that their bones are breaking
during the episode of dengue.
Now, there are 4 serotypes of dengue
and infection with 1 of those will cause
the first dengue syndrome,
the Break Bone Fever.
However, reinfection with a 2nd
or a 3rd or a 4th of the serotypes
causes a new process, which
always has some degree of hemorrhage,
hemorrhagic shock, multi-organ failure, etc.
So, to be infected with 1 is bad enough.
A 2nd or 3rd infections, many
times, can be fatal.
This is caused by the yellow
fever virus, also
carried by the Aedes mosquito.
Its primary focus of infection,
its tissue tropism,
is the liver.
And of course, because of that, patients
become jaundiced, hence, yellow.
Primary infection with high fever,
rapid onset of jaundice,
black vomit due to gastrointestinal
So, even though there isn't a primary
vascular focus for this,
yet still, due to backup congestion,
there can be bleeding into the stomach
bleeding into the gut,
and one can have black vomit and
indeed, black stools.
The prevention for this
is actually accomplished with a live
which currently is required,
not upon entry
to, but on departure from
a country which is afflicted or endemic
with yellow fever
prior to returning to a country which
has no yellow fever.
And now there are several here and will
include St. Louis encephalitis
virus and West Nile virus.
These are carried by the Culex, that larger
mosquito that we talked about,
and their focus, their tissue tropism,
is the central nervous system.
So, of course, patients with these viruses
will have your typical viral syndrome:
fever, headache, but they'll progress to
neck stiffness -- nuchal rigidity --
followed by loss of consciousness or
So, stupor, disorientation,
they may enter coma, they may
certainly, potentially a spastic
West Nile virus, especially, seems to
mimic, in some ways,
Guillain-Barre syndrome, so an
And some patients will present
confusion hallucinations and
urinary retention because they've had,
sort of, a paralysis
of the motor control allowing for
urinary let down.
And then Zika virus.
We're probably all currently
familiar with Zika virus at the time
of this filming,
primarily because of a fairly
in the Rio de Janeiro region of Brazil.
But, of course, Zika virus is historic
and has caused
outbreaks in other parts of the world.
It is carried by the Aedes aegypti
or a Aedes albopictus mosquitoes,
And there are several areas of tissue
tropism which you see listed there.
Indeed, the brain, the eye, the
body fluids, sexual organs,
the whole body can be affected,
and especially, infants born to mothers
who have been Zika infected
can have prominent findings
and demonstration by PCR a viral presence
in every tissue system present.
However, primary Zika virus in the non-
infants, a non-congenitally infected baby,
is a relatively mild process.
Patients will have conjunctivitis
which does not
have any discharge.
They'll have low grade fevers.
They'll have a rash, and they may also have
some arthralgias, all of which starts in
the periphery, so hands and feet
and move to the central region.
Adult patients with Zika virus
frequently do not seek medical
attention because most
are a very low level of severity.
because they are transiently immuno-
suppressed may have a more severe
collection of disease symptoms,
and certainly, they can transfer
disease to their infants.
The classic finding in
congenital Zika virus
is microcephaly, and not just a little,
but severe microcephaly,
more than 3 SDs
below the normal mean for head
circumference for the baby.
And there also have been many evidences
of miscarriage and birth.
So, these viruses, a full range, again, from
hepatitis -- one of the classic
parenteral or sexually acquired
all the way to mosquito or
which have a wide variety of tissue targets.
It again goes to show
that even the same family of virus could
have multiple different targets.
Very much the unintentional dinner guest.