B19 Parvovirus – Parvoviruses

by Sean Elliott, MD

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    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.

    00:54 The most common disease caused by B19 parvovirus is erythema infectiosum, which most people call fifth disease.

    01:03 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.

    01:17 There are fairly discrete clinical progressions of the virus.

    01:22 First, it starts as a very nonspecific flu-like illness.

    01:25 So, low grade fever, some generalized malaise, aches and pains, I mean, your typical, classical viral mess.

    01:34 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.

    01:53 After several weeks, an immune-mediated phase develops and this is where things get exciting and very specific.

    02:01 A rash develops and in many people, polyarthralgias, multiple joints become swollen.

    02:07 The rash is classic, and you will hear this and this will be tested on many, many exams.

    02:12 A slapped cheek rash.

    02:14 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.

    02:24 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.

    02:33 And the rash when it is complete, looks to be red or erythematous, slightly raised plaques, non-pruritic, very prominent.

    02:44 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.

    02:56 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.

    03:19 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.

    03:30 Rarely, we see some very severe complications related to B19 parvovirus, and this has to do, again, with its target, that progenitor of the red blood cell.

    03:40 Some patients may develop an aplastic crisis.

    03:44 These are especially those who already have underlying abnormalities of their bone marrow or production of erythrocytes.

    03:52 For example, patients with sickle cell disease, others with a chronic, underlying hemolytic anemia.

    03:59 These patients when they get infected with B19 parvovirus, may have a transient, reticulocytopenia.

    04:05 Reticulocytes, those progenitors, occurring over 7-10 days, followed by an arrest or stoppage of release of fully formed erythrocytes afterwards.

    04:17 This means that their already somewhat low levels of erythrocytes will plummet precipitously, and they will become severely anemic.

    04:26 During these 7-10 days of the reticulocytopenia, they may have fevers along with your typical malaise, etc., and so forth.

    04:35 They may have a rash, which is immune-mediated.

    04:38 They may have the arthralgias and joint swelling which are immune-mediated, so very much like primary fifth disease with the parvovirus.

    04:47 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.

    05:00 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.

    05:11 So, most at risk are those pregnant women, especially, early in their pregnancy, so before the 20th week of gestation.

    05:19 In those women, the parvovirus can either create an antibody reaction in the mother which crosses to the baby and destroys erythrocytes, or the baby itself may become infected with parvovirus and destruction occurs within the fetus.

    05:37 Regardless of the mechanism, babies born to mothers primarily infected with parvovirus may come out with a condition known as hydrops fetalis.

    05:47 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.

    06:08 So a baby with hydrops fetalis has total anasarca, edema throughout, and also involving the internal organs, and they are many times very sick.

    06:20 In fact, stillbirth or fetal loss occurs 10% of the time.

    06:24 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.

    06:44 Beware of parvovirus B19.

    About the Lecture

    The lecture B19 Parvovirus – Parvoviruses by Sean Elliott, MD is from the course Viruses.

    Included Quiz Questions

    1. Linear, single-stranded DNA
    2. Linear, double-stranded DNA
    3. Circular, single-stranded DNA
    4. Circular, double-stranded DNA
    5. Circular, single-stranded RNA
    1. ...erythroid precursor cells.
    2. ...lymphoid precursor cells.
    3. ...radial glial cells.
    4. ...pancreatic progenitor cells.
    5. ...endothelial progenitor cells.
    1. Erythema infectiosum
    2. Erythema toxicum neonatorum
    3. Erythema induratum
    4. Erythema multiforme
    5. Erythema nodosum
    1. Transient reticulocytopenia
    2. Transient lymphopenia
    3. Transient thrombocytopenia
    4. Transient reticulocytosis
    5. Transient lymphocytosis

    Author of lecture B19 Parvovirus – Parvoviruses

     Sean Elliott, MD

    Sean Elliott, MD

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