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Transmission Methods

Through mosquito bites

Zika virus is transmitted to people primarily through the bite of an infected Aedes species mosquito (Ae. aegypti and Ae. albopictus). These are the same mosquitoes that spread dengue and chikungunya viruses.

  • These mosquitoes typically lay eggs near standing water in things like buckets, bowls, animal dishes, flower pots, and vases. They prefer to bite people, and live indoors and outdoors near people.
    • Mosquitoes that spread chikungunya, dengue, and Zika bite during the day and night.
  • Mosquitoes become infected when they feed on a person already infected with the virus. Infected mosquitoes can then spread the virus to other people through bites.

From mother to child

  • A pregnant woman can pass Zika virus to her fetus during pregnancy. Zika is a cause of microcephaly and other severe fetal brain defects. We are studying the full range of other potential health problems that Zika virus infection during pregnancy may cause.
  • A pregnant woman already infected with Zika virus can pass the virus to her fetus during the pregnancy or around the time of birth.
  • Zika virus has been found in breast milk, and there have been several reports of Zika virus infection in babies from breastfeeding.1,2,3 However, there have been no reports of health problems in babies resulting from breastmilk from a mother with Zika virus infection. Because current evidence suggests that the benefits of breastfeeding outweigh the risk of Zika virus spreading through breastmilk, CDC continues to encourage mothers to breastfeed, even in areas with risk of Zika. CDC continues to study Zika virus and breastmilk and will update recommendations as new information becomes available.

Through sex

  • Zika can be passed through sex from a person who has Zika to his or her partners. Zika can be passed through sex, even if the infected person does not have symptoms at the time. Learn how to protect yourself during sex.
    • It can be passed from a person with Zika before their symptoms start, while they have symptoms, and after their symptoms end.
    • Though not well documented, the virus may also be passed by a person who carries the virus but never develops symptoms.
  • Studies are underway to find out how long Zika stays in the semen and vaginal fluids of people who have Zika, and how long it can be passed to sex partners. We know that Zika can remain in semen longer than in other body fluids, including vaginal fluids, urine, and blood.

Through blood transfusion

  • To date, there have not been any confirmed blood transfusion transmission cases in the United States.
  • There have been multiple reports of blood transfusion transmission cases in Brazil. These reports are currently being investigated.
  • During the French Polynesian outbreak, 2.8% of blood donors tested positive for Zika and in previous outbreaks, the virus has been found in blood donors.

Through laboratory and healthcare setting exposure

  • Prior to the current outbreak, there were four reports of laboratory acquired Zika virus infections, although the route of transmission was not clearly established in all cases.
  • As of June 15, 2016, there has been one reported case of laboratory-acquired Zika virus disease in the United States.
  • To date, no cases of confirmed Zika virus transmission in healthcare settings have been reported in the United States. Recommendations are available for healthcare providers to help prevent exposure to Zika virus in healthcare settings.

Risks

  • Anyone who lives in or travels to an area with risk of Zika and has not already been infected with Zika virus can get it from mosquito bites. Once a person has been infected, he or she is likely to be protected from future infections.
  1. Blohm GM, Lednicky JA, Márquez M, et. al. Evidence for Mother-to-Child Transmission of Zika Virus Through Breast Milk. Clinical Infectious Diseases. In Press. https://academic.oup.com/cid/advance-article/doi/10.1093/cid/cix968/4782287
  2. Gregory CJ, Oduyebo T, Brault AC, et. al. Modes of Transmission of Zika Virus. The Journal of Infectious Diseases. https://academic.oup.com/jid/article/216/suppl_10/S875/4753669
  3. Colt S, Garcia-Casal MN, Peña-Rosas JP, et. al. Transmission of Zika virus through breast milk and other breastfeeding-related bodily fluids: A systematic review. PLOS Neglected Tropical Diseases. http://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0005528
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