00:01
The B19 parvovirus, a virus.
00:05
Primate erythroparovirus 1 or for humans,
B19 parvovirus
are nonenveloped, and they are the smallest
DNA viruses which we have yet discovered.
00:16
They possess an icosahedral capsule
or capsid, with a linear, single-
stranded genome.
00:22
So unlike many of the other DNA
viruses we talked about,
these are single-strand genome.
00:28
Transmission of B19, or parvovirus,
is via respiratory droplets,
but also can be transplacental, as we'll
see with congenitally-acquired disease.
00:39
And the pathogenesis has to
do with the target cell
of B19 parvovirus, which is an erythroid
precursor cell.
00:48
So, those progenitors of erythrocytes
are red blood cells.
00:53
There are five syndromes or diseases which
are definitively associated with or caused by
parvovirus. B19.
01:00
The first is the most common fifth disease,
otherwise known as erythema infection
seen in children.
01:06
The second is a transient aplastic crisis in
those, especially with chronic hemolytic
disorders. The third is a foetal infection,
so affecting babies born to infected
moms which can cause non immune drops,
fatalis cardiomyopathy,
intrauterine fetal death or miscarriage.
01:23
The fourth is arthroplasty and or arthritis,
multiple joints at the same time
with or without a rash.
01:29
And this is more common in adult women and
men.
01:32
And then the fifth is a pure red blood cell,
a plasma, especially seen in chronically
infected immunocompromised individuals.
01:41
The most common disease
caused by B19 parvovirus is
erythema infectiosum,
which most people call fifth disease.
01:50
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.
02:04
There are fairly discrete clinical
progressions of the virus.
02:08
First, it starts as a very nonspecific
flu-like illness.
02:12
So, low grade fever, some generalized malaise,
aches and pains, I mean, your
typical, classical viral mess.
02:21
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
those progenitors.
02:40
After several weeks, an immune-mediated
phase develops and this is where things
get exciting and very specific.
02:48
A rash develops and in many people,
polyarthralgias, multiple
joints become swollen.
02:54
The rash is classic,
and you will hear this and this will
be tested on many, many exams.
02:59
A slapped cheek rash.
03:01
Unfortunately, it means, just as you
see in the image on the right of this
adorable infant
that the rash or that the cheeks look
like they have been slapped.
03:11
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.
03:20
And the rash when it is
complete, looks to be
red or erythematous, slightly raised plaques,
non-pruritic, very prominent.
03:31
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.
03:42
and now they're in the recovery phase.
But by that time, they've already
been contagious,
In adults, the adults may
miss or skip the rash,
but their immunologic reaction will
create even more prominent
joint complaints
So, not just arthralgia, but frank arthritis,
severe pain, swelling,
limitation of function, etc.
04:06
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.
04:17
Looking more closely at these
diseases caused by parvovirus b
19. The transient aplastic crisis,
thankfully, is transient.
04:24
It can be seen especially in individuals
with underlying sickle cell disease or
other chronic hemolytic anemic disease.
04:32
The pathogenesis is due to the virus itself
being cytotoxic to
erythrocytes red blood cells and especially
to young erythrocytes the
precursors. So as an immune reaction occurs
against the bound
virus, there is a transient reticulum utopia
lasting for even 7 to
10 days. And this, of course means that
there are decreased hemoglobin
carrying cells erythrocytes in the
periphery.
04:59
Clinically, patients with transient aplastic
crisis will experience
fever, malaise, itching, chills, a macula,
papua rash
and then also arthralgia and or just joint
swelling.
05:13
Hydrops fetails. This is perhaps the most striking
clinically when one sees it in
a fetus.
05:19
This occurs when babies are born to women
who were infected with parvovirus
19, especially before the 20th week of their
gestation.
05:29
The virus then crosses the placenta.
05:31
It can cause a non immune destruction of red
blood cells within the fetus.
05:36
This then has decreased oxygen carrying
capacity but also decrease osmotic load
within the vascular structures of the baby
and can leave to lead to high
drops fatal so extensive a.k.a of the baby
as well as cardiac
failure, multi organ dysfunction, severe
anemia, etc..
05:54
On the other hand, depending on when mother
is infected and the degree of non immune
destruction, the baby could actually be
asymptomatic with no abnormalities
whatsoever. However, this is perhaps the
worst one because there
is a risk of fetal loss at about 10%,
typically due to
stillbirth and or pre delivery miscarriages.
06:16
Looking then at arthralgia, this typically
occurs preferentially in adult women,
followed by adult men and then children.
06:23
And this also is due to deposition of immune
complexes on the
erythrocytes due to an antigen antibody
interaction triggered by the parvovirus B19.
06:34
These patients will experience painful and
stiff joints for approximately three weeks or
so, typically affecting small joints of the
hands and feet, but also wrists
and knees. So sort of think of a peripheral
poly arthralgia poly arthritis
over three, four, 75% also will develop a
rash, which can be a
lacie erythematosus macula rash, but
sometimes papules can be seen as well.
06:59
And then patients experiencing pure red
blood cell, a plasma.
07:02
These are almost exclusively
immunocompromised individuals who have an
inability to clear the parvovirus.
07:08
B 19 viremia from their bloodstream, leading
to
chronic or continually reactivated
parvovirus.
07:16
B 19 infection.
07:18
And again there's that targeting of red
blood cells and especially red blood cell
precursors, those reticular sites which are
so premature, this then can
lead to a persistent, severe and either
acute or chronic life threatening anemia.
07:33
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.
07:52
Beware of parvovirus B19.