HSV in pregnancy / neonatal HSV

• HSV is included in the “TORCH” causes of congenital infection, however this is a misnomer because intrauterine infection is very rare. HSV is mostly a concern in pregnancy due to the risk of neonatal acquisition at the time of delivery.
• The risk of transmission is highest if the mother is infected with HSV-1 or -2 for the first time (primary infection) close to delivery. Recurrent genital infection, or primary infection before 30 weeks, poses a much lower risk.
• There are three patterns of neonatal disease, which can be present individually or in combination: skin/eye/mouth, central nervous system, and disseminated disease.

The risk of transmission is highest with primary infection close to delivery because:

• The amount of virus in the maternal genital tract tends to be much higher.
• The mother has not had time to generate protective antibodies to pass on to the neonate prior to delivery.

• In women with a known history of genital HSV, testing is not required.
• In women with a possible primary episode of HSV during pregnancy, testing to confirm the diagnosis is recommended.
• Testing of infants is recommended if there are clinical features suggestive of HSV disease, or there was high risk of transmission at birth e.g. primary maternal infection after 30 weeks. This should be guided by a specialist.

Viral swab of base of lesion for HSV PCR (need to obtain vesicle fluid or cellular material on swab)

• Good sensitivity – a negative result on an adequately collected sample makes the diagnosis very unlikely
• Excellent specificity – a positive result confirms the diagnosis, and also determines HSV-1 vs -2 status

If the PCR is positive and gestation is >30 weeks, then HSV serology should also be sent

• If serology for the PCR-detected HSV type (1 vs 2) is:
  • positive = consistent with recurrent infection
  • negative = consistent with primary infection

Women with possible primary infection after 30 weeks gestation should be discussed with an obstetrician.

There are two main scenarios:

• Testing due to signs or symptoms of possible neonatal HSV disease
  • Skin/eye/mouth disease
    • Viral swabs of any skin lesions for HSV PCR
  • Central nervous system disease
    • HSV PCR on CSF
  • Disseminated disease
    • HSV PCR on blood
  • Given the possibility for overlap, testing is often done for >1 of the above.
  • PCR has high sensitivity and specificity, so is good for ruling in or out the diagnosis.
• Testing in asymptomatic infants with high-risk delivery
  • Surface ‘screening’swabs for HSV PCR
    • Eye, throat, umbilicus, rectum
    • These should be collected at >24 hours of age to avoid detecting possible residual maternal HSV DNA from the birth canal.
    • Note that negative screening swabs do not exclude the possibility of subsequent development of HSV disease
  • In some particularly high risk situations, CSF or blood may also be sent for HSV PCR

HSV serology outside the above recommendation

• This has no role as part of general ‘TORCH’ testing for congenital abnormalities, nor for infant diagnosis.