Neurological Consequences of Zika


Although not scientifically proven, there is a strong causal relationship between Zika infection and two severe neurological disorders.

Much recent news has focused on the Zika virus and the neurological problems it may cause. What are the risks, and what precautions should be taken by neurologists?

Zika virus spreads through mosquito bites, specifically Aedes aegypti and Aedes albopictus mosquitos, a variant typically found in the Americas, including portions of the USA. Symptoms of infection include fever, rash, pain in the joints, and conjunctivitis, rarely severe enough to require hospitalization. About 80% of those infected through mosquito bite experience no symptoms at all. However, some people infected with Zika may develop Guillian-Barré syndrome, an autoimmune disease that can cause weakness and even paralysis. The link between Zika and Guillian-Barré is not yet clear.

Although the symptoms of Zika-related illness are typically mild or non-existent, neurological consequences for unborn infants of mothers infected with Zika can be severe. Infants can develop birth defects including microcephaly. Transmission from mother to child is intrauterine; no transmission via the breast milk has been documented so far.

In Brazil, cases of microcephaly have roughly doubled in 2015, potentially due to Zika outbreak.1 The first report of Zika infection in Brazil occurred in March of 2015. Although it was initially unclear whether or not a link existed between Zika infection and birth defects, on February 1, 2016, the World Health Organization announced an International Public Health Emergency, based on the “spike in cases of microcephaly and Guillian-Barré syndrome in the Americas.” An emergency committee “agreed that a causal relationship between Zika infection during pregnancy and microcephaly is strongly suspected, though not scientifically proven.”2

Countries in which active infection has been reported include Mexico, several countries in Central and South America, American Samoa, Samoa, Tonga, and Cape Verde, Africa. A full list of those countries with active Zika transmission can be found on the CDC website.

The Centers for Disease Control and Prevention (CDC) developed recent guidelines to aid US-based healthcare providers treating infants at risk for Zika virus infection.3 The CDC recommends Zika virus testing for those mothers at risk, which means anyone who has been in areas with ongoing Zika virus transmission during pregnancy, even if they never had symptoms of Zika infection. This includes reviewing fetal ultrasounds for microcephaly or intracranial calcifications and maternal testing for Zika virus infection. If maternal Zika infection is confirmed, the CDC recommends fetal ultrasounds every 3-4 weeks.4

Infants with cranial abnormalities including microcephaly and intracranial calcifications should also be tested for Zika virus infection. Healthcare providers need to contact state or territorial health departments to record the infection. Testing for Zika virus infection is performed both through molecular and serologic testing, including “reverse transcription-polymerase chain reaction (RT-PCR) for viral RNA, and immunoglobulin (Ig) M ELISA and plaque reduction neutralization test (PRNT) for Zika virus antibodies” according to the CDC.3

As of February 3, 2016, 35 Zika virus cases have been reported in the United States, and no locally-acquired cases. There is no vaccine or medicine that can prevent Zika infection.

People travelling to, or residing in, areas with active Zika infection should be advised to wear long pants, long-sleeved shirts, and permethrin-treated clothing, and use insect repellents to avoid mosquito bites.



1. Dyer O. Zika virus spreads across Americas as concerns mount over birth defects. BMJ 2015;351:h6983.

2. World Health Organization. Latest Zika situation report. Feb 5, 2016.

3. Interim guidelines for the evaluation and testing of infants with possible congenital Zika virus infection - United States, 2016. Centers for Disease Control and Prevention. Jan 29, 2016.

4. Interim Guidelines for Pregnant Women During a Zika Virus Outbreak - United States, 2016. Centers for Disease Control and Prevention. Jan 22, 2016.

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