Transmission: How Zika Virus Spreads

  • The most common way Zika virus spreads is by infected Aedes mosquitoes.
    • Aedes aegypti and Aedes albopictus mosquitoes live throughout the United States, especially in warmer and wetter states of the southern and Gulf Coast regions.
    • Aedes tend to bite during the day and at night, both indoors and outdoors.
    • Aedes are the same mosquitoes that spread dengue fever and chikungunya.
  • Zika virus can also be passed through sex (sexual transmission).
    • An infected person can pass Zika virus to his or her partners during unprotected vaginal, anal, or oral sex or through the use of sex toys, even if they don’t have symptoms.
    • Zika virus can stay in semen longer than in blood.
  • A pregnant woman who has Zika virus can pass it to her developing baby.
    • Zika infection during pregnancy can cause severe birth defects, called ‘congenital Zika syndrome.’
    • Babies with congenital Zika syndrome might have microcephaly (small head and brain), damage to the brain’s growth and development, vision problems, hearing loss, joints that do not move properly (called contractures), rigid muscle tone that restricts body movement, and/or seizures.
    • Not every baby born to a mother with Zika virus will have congenital Zika syndrome. We are learning more about the amount of risk and how the risk might be different depending on when in the pregnancy the Zika infection happens.
  • Zika virus has been found in the breastmilk, but there are no reports of infants getting Zika from breastmilk. Women are encouraged to breastfeed their babies, even if they live in an area with a risk of Zika.
  • Zika may be passed through blood transfusion with infected blood, but all blood donated in the U.S. and Puerto Rico is tested for Zika.
  • Only about 1 out of every 5 people infected with Zika will have symptoms.
    • Symptoms begin 3-7 days after a bite by an infected mosquito; last for several days to a week.
    • Zika is usually a mild illness with fever, rash, joint pain and conjunctivitis (red eyes). Zika may also cause muscle pain, headache, pain behind the eyes and vomiting.
    • Symptoms can be treated, but there is no cure or vaccine for Zika.