Parvovirus B19

Question 1

Define

Answer 1

Erythema infectiosum (AKA ‘fifth disease’) caused by parvovirus B19 (a small ssDNA virus)

Incubation period 4-20 days; infective from 10 days prior of rash until 1 day after appearance of rash

Risk period if vertically transmitted <20w GA; low risk >20w

 

Aetiology – transmission by aerosol route, also blood-borne

Risk factors – children and susceptible adults

Epidemiology – common, 60% immunity in adults by age 20

Question 2

Signs and symptoms

Answer 2

In the young child / mother:

• Asymptomatic in most cases
• Rash, malaise, fever, arthralgia, transient aplastic crisis (however, 25% asymptomatic)
• Rash – commonly ‘slapped cheek’ appearance (erythema infectiosum)
• Infant – coryzal symptoms, headache, rash

In the neonate / antepartum:

• Produces mild self limiting infection in adults but can cause spontaneous miscarriage or IUD if transmitted to the foetus
• B19 crosses placenta (4-20w GA) and destroys RBCs  hydrops fetalis  10% infant mortality
• Treat with intrauterine transfusions
• No other CNS damage so if treated with transfusions, many infants are completely fine

Question 3

Investigations

Answer 3

(if exposed after 20w, no investigations are needed as very low risk):

Routine screening not recommended

Viral DNA PCR - MOST accurate

• Use maternal serum/blood + resp samples

IgM and IgG  if -ve IgG and -ve IgM, re-check in 1m [if +ve IgM B19  serial USS]

• Infection must be confirmed by atleast 2 samples

USS  foetal anomaly scan 4 weeks after onset of illness, then serial scans in 2-week intervals until 30/40

Rubella serology (similar presentation)

Question 4

Management

Answer 4

Maternal and infant  self-limiting (clears up in 3w) - supportive treatment with paracetamol and plenty of fluids

Intrauterine

• If confirmed infection of parvovirus B19, refer to foetal medicine specialist within 4 weeks for monitoring foetal growth and assessing for complications
• The main risk of foetal parvovirus infection is FOETAL HYDROPS
• Serial USS and Doppler assessment
  
  • Start at 4 weeks post-infection or at 16 weeks, repeating every 1-2 weeks until 30 weeks gestation
• If there is evidence of foetal hydrops on USS- REFER to tertiary centre for IU erythrocyte transfusion
  
  • A hydropic foetus may recover spontaneously or may require IU transfusion 
• If anaemia is treated by intrauterine transfusion, foetus can make a complete recovery

Question 5

Complications

Answer 5

miscarriage (15%), foetal hydrops (3%)