B19 Parvovirus – Parvoviruses

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.