Zika virus exposure in pregnacy:
Management of Infants
|Reviewed by Simon Rowley & Lesley Voss|
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).
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.
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.
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.
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.
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|