Zika Virus



  • Zika virus is a single-stranded RNA virus (family Flaviviridae).
  • Transmitted by Aedes spp. mosquitoes (especially Aedes aegypti), which also transmit dengue and chikungunya
  • Incubation estimated to be several days to a week
  • 80% of infections are asymptomatic.
  • Symptomatic illness: acute onset of fever, maculopapular rash, joint pain, and/or conjunctivitis
  • Generally mild; symptoms: several days to a week
  • Zika virus infection in pregnant women can lead to fetal and newborn complications (see “Pregnancy Considerations”).
  • A link to Guillain-Barré syndrome (GBS) has been described.


  • 1950s: sporadic cases in Africa and Southeast Asia
  • 2007: outbreak of Zika virus in Yap island, Micronesia
  • 2013 to 2014: French Polynesia, >28,000 suspected Zika virus infections
  • 2015: Zika virus outbreak in Brazil, estimated 1.5 million cases
  • Current outbreak in the Americas, the Caribbean, and the Pacific
  • In United States, there has been imported Zika infection in travelers, mosquito-borne transmission (Florida and Texas), and sexually transmitted Zika virus infection (Texas). Zika-related congenital microcephaly has also been reported.

Etiology and Pathophysiology

  • Vector is Aedes spp. especially A. aegypti and Aedes albopictus mosquitos, aggressive daytime feeders; bites can also occur at night.
  • Other modes of transmission: maternal–fetal (intrauterine, perinatal); transfusion; sexual
  • Zika virus RNA can be found in serum, urine, semen, female genital tract secretions, saliva, and tears. Sexual transmission has been described 41 days after symptom onset.
  • Neurotropic in animals; can cause neural cell death
  • Coinfection with dengue and chikungunya virus is increasingly recognized and can lead to more severe disease.

Pregnancy Considerations

  • Pregnant women do not have more severe disease or increased susceptibility; however, persistent maternal viremia increases the risk of neurologic and cardiac abnormalities in the fetus. Pregnant women with possible Zika virus exposure (travel or residence history, possible sexual exposure before/during pregnancy) should have diagnostic (CDC algorithm) (1).
  • Symptomatic pregnant women should have Zika virus nucleic acid test (NAT) of serum and urine, and serum IgM serology as soon as possible, up to 12 weeks after symptom onset (1).
  • Asymptomatic pregnant women with recent possible Zika virus exposure do not require testing if they do not have ongoing possible exposure of the virus (1).
  • If asymptomatic pregnant women have ongoing possible Zika virus exposure, CDC recommends serum and urine Zika virus NAT 3 times during pregnancy with the first test obtained at initiation of prenatal care (1).
  • Fetal ultrasonography is recommended for all pregnant women with laboratory diagnosed or suggested/possible Zika virus infection to assess for fetal infection and/or congenital malformation.
  • Breastfeeding mothers with Zika virus infection
    • Zika virus RNA has been identified in breast milk.
    • No cases of Zika transmission associated with breastfeeding have been reported.
    • Current evidence suggests benefits of breastfeeding outweigh theoretical risks to infants.

Risk Factors

People living in, or traveling to, an endemic area not previously infected. Immunity will likely develop after initial infection.

General Prevention

  • Prevention via insect repellents/mosquito control and clothing that minimizes skin exposure, especially during daylight hours
  • Pregnant women should consider avoiding travel to areas with ongoing Zika virus outbreaks.
  • In areas with Zika virus transmission, individuals with a pregnant partner should avoid unprotected sex or abstain for duration of pregnancy.
  • With travel to area of ongoing Zika virus transmission, CDC recommends protected sex using condoms or abstinence for at least 6 months for men or 8 weeks for women, after symptom onset or last possible Zika exposure (2).
  • Inactivated vaccines are under development—in phase I trials, 92% of vaccine recipients had sero-conversion by day 57, with few side effects (3,4).

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