The B19 parvovirus, a virus.
Primate erythroparovirus 1 or for humans,
are nonenveloped, and they are the smallest
DNA viruses which we have yet discovered.
They possess an icosahedral capsule
or capsid, with a linear, single-
So unlike many of the other DNA
viruses we talked about,
these are single-strand genome.
Transmission of B19, or parvovirus,
is via respiratory droplets,
but also can be transplacental, as we'll
see with congenitally-acquired disease.
And the pathogenesis has to
do with the target cell
of B19 parvovirus, which is an erythroid
So, those progenitors of erythrocytes
are red blood cells.
The most common disease
caused by B19 parvovirus is
which most people call fifth disease.
The typical target for this
are younger children age 4, although
it can go up to age 15 or so,
and older adults can also acquire
B19 parvovirus in this way.
There are fairly discrete clinical
progressions of the virus.
First, it starts as a very nonspecific
So, low grade fever, some generalized malaise,
aches and pains, I mean, your
typical, classical viral mess.
But if somebody were to obtain
a complete blood count at
this stage, and there's no reason
they should, but if they were,
they would potentially see
decreased hemoglobin levels
or decreased erythrocytes,
because the virus is already starting to
create a lytic response to
After several weeks, an immune-mediated
phase develops and this is where things
get exciting and very specific.
A rash develops and in many people,
joints become swollen.
The rash is classic,
and you will hear this and this will
be tested on many, many exams.
A slapped cheek rash.
Unfortunately, it means, just as you
see in the image on the right of this
that the rash or that the cheeks look
like they have been slapped.
They're red, they're prominent, but the rash
starts there, and then it starts
to proceed down the trunk
and it spreads out to the extremities.
And the rash when it is
complete, looks to be
red or erythematous, slightly raised plaques,
non-pruritic, very prominent.
By this time, the kids are
over the initial viral
process and so they feel just fabulous,
as you can see from this young man
He's kicking back, smiling at the
camera, posing, of course.
and now they're in the recovery phase.
But by that time, they've already
In adults, the adults may
miss or skip the rash,
but their immunologic reaction will
create even more prominent
So, not just arthralgia, but frank arthritis,
severe pain, swelling,
limitation of function, etc.
And as you can see on the slide, it
can affect most joints, but especially
the peripheral joints, so wrists, ankles,
anywhere in the hands, sometimes the knees.
Rarely, we see some very severe
to B19 parvovirus, and this has to do,
again, with its target, that progenitor
of the red blood cell.
Some patients may develop
an aplastic crisis.
These are especially those who already
have underlying abnormalities
of their bone marrow or production
For example, patients with
sickle cell disease,
others with a chronic, underlying
These patients when they get
infected with B19 parvovirus,
may have a transient, reticulocytopenia.
Reticulocytes, those progenitors,
occurring over 7-10 days,
followed by an arrest or stoppage
of release of fully formed
This means that their already
somewhat low levels
of erythrocytes will plummet precipitously,
and they will become severely anemic.
During these 7-10 days of
they may have fevers along with your
typical malaise, etc., and so forth.
They may have a rash, which
They may have the arthralgias
and joint swelling
which are immune-mediated, so
very much like primary fifth
disease with the parvovirus.
But they have this underlying process
which is even far more severe,
and they'll develop symptomatic anemia
shortly after the reticulocytopenia
starts to resolve.
The other major complication of B19
parvovirus then is how it affects
babies born to mothers who become infected
for the first time with B19 parvovirus.
So, most at risk are those pregnant
women, especially, early in their
pregnancy, so before
the 20th week of gestation.
In those women, the parvovirus can either
create an antibody reaction in the mother
which crosses to the baby and
or the baby itself may become
infected with parvovirus
and destruction occurs within the fetus.
Regardless of the mechanism,
babies born to mothers
primarily infected with parvovirus
may come out with a condition
known as hydrops fetalis.
This is where the baby's had
severe destruction of
erythrocyte precursors in utero,
and were born with a very low
circulating blood volume
in terms of red blood cells, which
means that all the fluids
leaked out of the blood vessels
because there is no oncotic
pressure to retain them within
the blood vessels.
So a baby with hydrops fetalis
has total anasarca,
edema throughout, and also
involving the internal organs,
and they are many times very sick.
In fact, stillbirth or fetal loss
occurs 10% of the time.
So, B19 parvovirus in general is a routine,
benign, self-resolving viral illness
which affects primarily children,
but it can be quite severe
when it affects those
who have underlying hemolytic abnormalities,
or those babies born to mothers
with primary infection.
Beware of parvovirus B19.