Parvovirus B19

Fifth Disease
Classic Case: Child with Parvo B19

Young child presents with a macular rash on his face, arms, and torso. It has a lacy appearance, and a distinct border. The child is otherwise completely healthy, but had a non-specific respiratory/febrile illness a few weeks prior. May or may not be accompanied by joint pain.

Causative Agent of:
  • Fifth Disease: a childhood rash
  • Hydrops fetalisfatal disease in fetus
  • Aplastic crisis: dangerous drop in RBC counts
  • Also called Parvo B19, or B19
  • Recently renamed Erythrovirus B19
    • It infects erythrocyte progenitors
Why is it called fifth disease?

Before modern medicine, macular rashes were classified numerically based on appearance/symptoms alone: 1st, 2nd, 3rd disease, etc.

  • 1st : Measles
  • 2nd: Scarlet fever
  • 3rd: Rubella
  • 4th: Dukes’-Filatov (no longer a recognized illness)
  • 5th: Parvovirus
  • 6th: Roseola
Physical Features
  • Genome: ssDNA
  • Structure: Non-enveloped
  • Family: ParvoviridaeIs the only significant human Parvovirus; Other Parvoviridae species can infect other animals, such as dogs
Epidemiology
  • Common childhood infection
  • > 60% of adults are seropositive
  • Seasonality: Cases most common in spring
Reservoir and Transmission

Reservoir:

  • Humans only

Transmission:

  • Respiratory droplets, person-person
  • Very contagious disease
Risk Groups
  • Children most at risk of infection
  • Risk of Serious Infection:
    • Anemia pts (sickle cell, etc.)
    • Immunosuppressed (e.g. AIDS)
    • Fetus (2nd trimester)

Clinical

Parvo (Erythrovirus) B19
Fifth Disease: Children
  • Incubation period:  <1 week
  • Prodrome: Low fever, chills, malaise, headache for 2-3 days
  • 2-3 weeks after recovery:
    • Lacy erythematous maculopapular rash, begins on face
    • biphasicTwo periods of symptoms separated by a healthy period illness
    • Rash appears 2-3 wks post-recovery
    • “Erythema infectiousum”
    • Slapped cheekBuzz-word” appearance of rash; arms, trunk also
    • Rash is most common B19 symptom
    • Ag-AbAntigen-Antibody complexes deposit in skin = inflammation and rash
    • Typically kids aged 4-14
Temporary Arthritis: Adults
  • Seen mostly in adults (females > males)
    • 2 wks post-infection
  • Acute symmetrical joint pain
    • Usually small joints:
    • Hands, wrists, ankles, knees also
  • Recovery in 1-3 weeks, but can recur for months
  • Often mimics rheumatoid arthritis
Aplastic Crisis: Anemic or Immunosuppressed
  • Chronic hemolytic anemia:
    • Bone marrow stressed to make RBCs
    • Exacerbated anemia, then rash, pancytopenia
    • Serious illness, but most completely recover
  • Immunosuppressed:
    • Pure Red Cell Aplasia (PRCA)
      • A persistent RBC aplasia/anemia
    • No immune response = continual RBC infection/death
    • Life-threatening
    • No arthralgia or Fifth Disease rash
    • (these are immune system-mediated)
Hydrops Fetalis: The Fetus
  • Fetal death in 10% of pregnant infected women
  • But, no known congenital abnormalities
  • Virus infects RBCs in fetal liver
    • (Where hematopoesis occurs in 2nd trimester)
    • 2nd trimester = greatest risk
  • Accumulation of fluids in fetal tissues due to RBC death
Pathogenesis
  • Respiratory inoculation
    • Viremia to blood and bone marrow
    • Parvo B19 likes to infect red blood cell precursors
    • (Hence the new name “erythrovirus” B19)
    • A lytic infection, so RBCs die = anemia
  • Virus entry receptor?
    • Blood group P antigen (globoside)
  • RBC disorders?
    • (e.g. chronic anemia, sickle cell)
    • = Big RBC drop (anemia)
    • But immune system eventually kills virus
  • Immunosuppressed pts?
    • = Chronic anemia
    • No immune system? No killing of virus!
    • Anemia can be deadly
  • Immune response?
    • Large antibody production
    • = Type IV hypersensitivity reaction
    • Ag-Ab complexes
    • = Joint pain, rash (fifth disease)
Diagnosis
  • Clinical signs
  • Serology or PCR
    • 90% detection by 3rd day of symptoms
    • Usually reserved for serious infections
Prevention and Treatment

Prevention:

  • Good hygiene (hand washing)
  • No vaccine available
  • Virus is cleared before rash
    • So isolating children with rash is useless
    • Is therefore difficult to control
    • Advise pregnant women of risks at schools/day cares

Treatment:

  • Supportive only, no antivirals
  • Ig for chronic parvovirus in immunocompromised

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