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Zika virus - exposure in pregnancy

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Zika virus was isolated in Africa in the 1940s but it was in the last decade that outbreaks have occurred, which then spread across the Western Pacific (French Polynesia, Tonga, Samoa and Fiji). It was only in 2016, with an outbreak in Brazil, that congenital Zika syndrome was identified. Zika virus is transmitted by mosquitoes, predominately Aedes mosquitoes (A. Egyptii and A. Albopictus) but also Anopheles and Mansonii, and can also spread through sexual contact, blood transfusions and laboratory exposure. Aedes mosquitoes have not been found in NZ. Zika virus is a notifiable disease. Notify all newly identified Zika cases to the Medical Officer of Health in Auckland (ph. 09 6234600).


  • Confirmed Zika virus infection: symptoms plus laboratory confirmation. 
  • Possible Zika virus infection: travel to, or residence in an area with risk for Zika virus transmission, or having unprotected sex with a partner who has travelled to or resides in an area at risk for Zika virus within 3 months1


Zika virus usually causes a mild self-limited illness, with acute onset of fever, rash, arthralgia and conjunctivitis. It is asymptomatic in 80% of cases, meaning that pregnant women may be unaware that they have been infected. Incubation period is estimated as 3-14 days. Pregnant women need to be tested by rRT-PCR for Zika virus RNA within 2 weeks of exposure or symptom onset (EDTA blood rRT-PCR < 7 days, urine rRT-PCR < 14 days) or by IgM within 2-12 weeks. Serology needs to be interpreted with caution due to cross reactions with other related flaviviruses eg. dengue, chikungunya. Negative testing 12 weeks after exposure does not rule out maternal infection. Rt-PCR test may remain positive for longer in pregnant women.

Major risk period - infection in the late first trimester and early 2nd trimester, but adverse outcomes have been associated with infection diagnosed in the third trimester. Reports suggest it can take from a median of 18-21 weeks from symptom onset to prenatal diagnosis of microcephaly on ultrasound.

Zika virus has been detected in breast milk but there are no reported cases of Zika virus in association with breastfeeding. Current evidence suggests that the benefits of breastfeeding outweigh the risks of Zika virus transmission and should be encouraged.

Congenital infection

The clinical spectrum of congenital Zika virus infection is not fully known. Zika virus appears to target neural progenitor cells disrupting neuronal proliferation, migration and differentiation, resulting in microcephaly and other serious brain anomalies. The neurologic anomalies seen have a pattern that enables distinction from the lesions commonly seen in other congenital infections. Other findings include ocular abnormalities such as chorioretinitis, hemorrhagic retinitis, optic nerve hypoplasia, clubfoot and arthrogryposis, likely as a consequence of the neurological abnormalities. More data is awaited regarding long term outcomes of those apparently unaffected or mildly affected.

Laboratory investigations for infants

Diagnostic testing for congenital Zika virus can be difficult. Suggest discussing with a virologist ( Dr Kitty Croxson 021758172 in Virology/immunology lab) prior to sending tests.

Amniotic fluid should be collected at delivery - 2ml of amniotic fluid in a sterile tube, submit promptly to the Virus Laboratory.

Testing from the infant (not cord blood) in first 2 days of life is recommended.

Tests include:

  • EDTA blood for rRT-PCR for Zika virus RNA 
  • Urine for rRT-PCR Zika virus RNA 
  • Serum on infant for Zika virus IgM ELISA 
  • If a CSF is done for other reasons - rRT-PCR for Zika virus RNA can be requested. 

A positive blood or urine rRT-PCR test confirms Zika virus infection, but a negative result does not rule it out. IgM results can be useful, if PCR negative, a positive IgM indicates probable infection although false positive IgM can occur.

Placenta can be considered for testing in a symptomatic pregnant women and when an infant has Zika virus associated birth defects without a definitive laboratory confirmed diagnosis in pregnancy.

Management in infants

  1. Mother and/or partner exposed to Zika virus in pregnancy
    If mother's results as yet unknown, perform a thorough examination, including occipital frontal circumference (OFC) while awaiting results. If the infant is clinically well, further testing as per below can be deferred until maternal test results have come back positive for Zika virus. If there is concern about follow-up of the infant or testing of the mother is 12 weeks after exposure do all Zika virus testing on the infant (blood, urine and consider CSF) as well as ophthalmology and head USS.
  2. Mother confirmed positive for Zika virus in pregnancy
    Blood and urine for rRT-PCR for Zika virus (consider Zika IgM also) from infant and careful physical examination including OFC and other measurements and check for dysmorphism. Check head USS, hearing screen as per universal screening.
  3. Infant not confirmed positive (negative IgM and rRT-PCR)
    Infant should receive routine care including regular OFC monitoring , neurological examination and age appropriate developmental screening.
  4. Infant confirmed positive for Zika virus 
    As per the above plus comprehensive ophthalmological examination and ABR hearing testing by one month of age. These infants should be followed for the first 12 months of life,( by Neonatal Service in consultation with SSH -ID) including repeat audiology at 6 months of age if initial screen negative. Appropriate referral and management if any abnormalities are found.
  5. Infants with clinical findings consistent with congenital Zika infection
    Extensive evaluation (as per point 4) needed in consultation with a paediatric neurologist. Infant requires ongoing follow-up. 

NZPSU surveillance

A NZPSU surveillance programme is currently in place for reporting of infants presenting with microcephaly and/or neurological abnormalities in the context of possible Zika virus exposure.


  1. CDC. Update: Interim guidance for health care providers caring for pregnant women with possible Zika virus exposure- United States July 2017 MMWR 24 July 2017 66: 
  2. CDC. Update: Interim guidance for the evaluation and management of infants with possible congenital Zika virus infection - United States, August 2016. MMWR. Aug 19th 2016 

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Document Control

  • Date last published: 01 August 2017
  • Document type: Clinical Guideline
  • Services responsible: Neonatology, Paediatric Infectious Diseases
  • Owner: Newborn Services Clinical Practice Committee
  • Editor: Sarah Bellhouse
  • Review frequency: 2 years