• mosquito-borne flavivirus, lineages include

    • African lineage

    • Asian lineage (most often found in Americas)

  • transmission

    • primarily by Aedes aegypti mosquito bite

    • human-to-vector-to-human transmission occurs during outbreaks

    • maternal-fetal

    • sexual transmission

    • blood or blood products

    • no cases of transmission reported during breast feeding (not yet well evaluated)

  • epidemiology

    • virus first isolated in 1947 from a macaque in Zika forest of Uganda

    • first human case reported in Nigeria in 1954

    • East African Zika virus likely spread to Southeast Asia around 1945

    • period of stable endemicity in Africa and Southeast Asia persisted in 20th century

    • first large-scale outbreak and eastward spread in 2007 on Yap Island, Micronesia

    • second major outbreak reported in French Polynesia in 2013-2014 

    • major outbreak presently ongoing in the Americas
      • first reported in Brazil in May 2015 (estimated 500,000 to 1.5 million persons infected)

      • outbreak now spread to Central and South America and Caribbean, including Puerto Rico.

      • international spread of Zika virus from Brazil likely to occur due to high volume of tourism and wide distribution of Aedes mosquito vectors 

      • local transmission not yet reported in mainland USA, but infections have been reported among travelers returning to USA from affected areas.

Clinical presentation and course

  • about 75% to 80% of infections asymptomatic

  • symptomatic disease generally mild

    • common symptoms include fever, rash, arthralgias and conjunctivitis

    • symptoms typically arise about 3 to 12 days after exposure and are self-limited, resolving in about 5 to 7 days

  • severe disease and need for hospitalization 

  • hemorrhagic fever not yet reported 

  • mortality extremely low in 2015-2016 Zika virus 
outbreak in Americas


  • fetal abnormalities reported in fetuses whose mothers acquired acute Zika virus infection during pregnancy include

    • microcephaly
      • incidence of fetal microcephaly in Brazil 

      • 5.7 cases per 100,000 live births in 2014

      • 99.7 cases per 100,000 live births in 2015

      • prevalence of microcephaly in infants born to women who resided in regions with active transmission during first trimester of pregnancy 2.8 cases per 10,000 live births, compared with infants born to women living in regions without confirmed Zika virus transmission (0.6 cases per 10,000 live births) during January 2015 and January 2016 

      • Zika virus RNA detected in placental and fetal tissue of those affected

    • other complications
      • intrauterine growth restriction

      • fetal death

      • cerebral calcification or other central nervous 
system lesions

  • Guillain-Barre syndrome 

    • increase in rate during outbreak reported but causal role not confirmed