The togaviridae, viruses.
The togaviruses are small,
enveloped, icosahedral capsules,
such as you see in front of you
on the electron microgram.
They have a linear, single-stranded,
positive-sense RNA genome,
and keep in mind that positive-sense
RNA functions as messenger RNA
in terms of its transcription.
There are several medically-relevant
viruses we'll talk about
under the togavirus heading.
One of those is the rubella virus,
the cause of German measles.
But then the arboviruses, which are
vector-associated, mosquito inserted
viruses, are also important.
And these include several
viruses known as the Eastern,
the Western, and Venezuelan
equine encephalitis virus,
and a recent fame,
chikungunya virus, which is
emerging in significance
as it comes across Central
and South America.
Let's start with rubella virus.
This infection starts by acquisition into
the upper respiratory tract,
typically by a respiratory or
a contact transmission,
, and it sets up its primary
or initial site of infection
in lymph tissue, in local lymph nodes
within the upper respiratory tract.
From there, comes the primary viremia,
which then allows for a diffuse
or disseminated skin rash
as a localized immunologic reaction.
There is, then, also a prodromal period
lasting for about 2 weeks,
as the new virions, the new
viruses are synthesized
within their cellular target,
and then released.
And during this time, the
are quite present and quite contagious.
So, the rashes first, but then it's followed
by a highly contagious period,
unlike some viruses which try to trick you
by being highly contagious prior
to the onset of the rash.
and intrauterine exposure
for congenital rubella
is probably the biggest problem
that we see with rubella virus
because the German measles
itself, as we'll see,
is not that significant.
However, congenitally-acquired rubella
because the virus can interfere with
normal development of
multiple fetal tissues
with significant teratogenic effects.
What does the disease look like?
Primary or, you know, typical
rubella or German measles transmitted,
again, by respiratory droplets
has as its rash,
a morbilliform rash, which simply
It's not very helpful, unless you look
at the picture in the upper right,
and that displays discreet
erythematous maculopapular lesions,
which are a darker pink than perhaps a
lighter salmon-colored or an allergic rash.
The rash, as it does with other viruses,
especially measles, begins at
the cranial region, begins at the head,
and then it moves slowly on down
toward the caudal region.
As it does so, a one -- the
patient develops a post-
auricular, so a post-cervical
Most children who suffer
from German measles
aren't stopped by this at all.
They're out playing, having fun,
exposing everybody else
to their lovely rubella virus.
Adults, however, will many
times develop a diffuse
bordering on arthritis by
the severity of the pain.
And they also may progress
to a thrombocytopenia
or a postinfectious encephalitis.
Prevention for this is accomplished through
the measles mumps rubella shot,
which is provided to children beginning
at 12-15 months of life,
followed by a booster at age 4-5.
That is a live attenuated vaccine,
and in terms of rubella, it has been highly
successful in preventing cases.
Those patients or those mothers
who had not been immunized
to rubella and develop acute
rubella during their pregnancy
are able to transmit the virus
to their fetus, to their baby.
And especially if that infection occurs,
and transfer occurs prior to
the 20th week of gestation,
the baby will demonstrate
some very significant effects.
In the lower right picture,
you see a baby with bilateral
cataracts, with the white
cataract material seen within the iris.
That is a very common expression or
manifestation of congenital rubella.
So, too, would be cognitive to
delay, a mental retardation
and sensory neural deafness like many other
congenitally-acquired viral infections,
The blueberry muffin spot
is a site of extramedullary hematopoiesis,
which is seen in the skin
and these lesions are somewhat raised.
They are dark red bordering on purple,
and they indeed are where
extra hematopoiesis, extra erythrocyte
derivation is occurring
outside of the bone marrow because
these patients are typically anemic.
In addition to those findings, central
core cardiac abnormalities may
occur, including a patent
ductus arteriosus, and even
coarctation of the aorta
So, this is a very significant process.
Children born with congenital rubella
have multiple challenges facing them
throughout the rest of their life.
Let's turn now to diseases caused
by the arboviruses, and we'll start
with Eastern equine encephalitis.
Keep in mind that all these are transferred
by the bite of an infected mosquito,
Eastern equine virus, or Eastern
by the Eastern equine encephalitis virus
starts with fever and headache, along with
vomiting, and progresses rapidly to include
elevated white blood cells and dizziness.
As the patients go further
into the immunologic
response to the virus, they'll develop
decreasing levels of consciousness,
accompanied by seizures
and focal neurological signs.
Patients who survive this, and most do,
but they're left with chronic convulsions,
as well as sometimes focal paralysis
and absolutely significant
challenges with cognition
bordering on mental retardation.
The Western equine encephalitis
Western equine encephalitis,
and here, most patients start off
either with an asymptomatic
prodrome or at the very worst,
a mild, flu-like illness,
so they may develop this altered
mental status out of the blue.
Many times, toward the end of the summer
after mosquito bites may have occurred,
they'll develop this change in consciousness.
They'll become weak.
They may develop some neck pain, neck
stiffness because of meningeal irritation,
Frequently, these patients come
to medical attention
with a concern for some form of meningitis,
but they then keep progressing
into somnolence, to coma.
Here, when the patients wake up,
and they may have required extended
medical care to do so,
they may be left with cognitive delay,
emotional instability, and spastic
paresis causing contractures.
Venezuelan equine encephalitis.
So here again, starting with
developing retro-orbital or occipital
headaches, leucopenia, tachycardia,
mostly a very severe flu-like illness,
but then they also progress
into somnolence, coma,
seizures, confusion, photo phobia,
the whole 9 yards.
You see a recurring theme here,
starting off flu-like,
progressing into aseptic
and then into coma.
And then long-term effects in Venezuelan
equine encephalitis will be
focal neurological damage,
causing some paresis,
focal neurological damage,
causing some paresis,
That may occur in others of the encephalitis
viruses we've just talked about,
but the numbers have been so low
that they've been poorly described.
However, in Venezuela, in which
surprise, surprise, most of our
information comes from,
there were a larger number
of people including
pregnant mothers, and so we have
some information about
perinatal acquisition of the disease.
And then chikungunya.
This also is carried by the bite, in this
case, of the Aedes mosquito
and these patients start off
with the high fevers.
The joint pain, though, and the rash,
which is another macular rash,
are quite peripheral.
In fact, if you look at pictures or even
see a patient with chikungunya,
they frequently are unable to walk
because the peripheral pain, the
ankles, the feet, the wrists,
is incredibly severe.
And unfortunately, there's a chronic
form, as you see there,
in which the pain keeps coming
back for months upon months.
Along with the severe peripheral
arthralgia and arthritis,
these patients also may have conjunctivitis,
headache, fatigue, etc.
Chikungunya is actually a
Swahili term which in very
rough translation means that which bends up,
which is a reference to just how
severely inflamed those joints are,
and just how painful the patients feel
when trying to walk.
So, we have here a collection of viruses
all which seem to have either
central nervous system or
the rubella, the focus on
rash and a congenital
or intrauterine transmission.
But overall, these are very
serious group of viruses
that can be transmitted very much un-
suspiciously and without prior warning.
So, the only recommendation
I have to you now is
put on your mosquito spray
when you go outside.