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Transmission & Risks

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 in and 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 are aggressive daytime biters, but they can also bite at 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.
  • To date, there are no reports of infants getting Zika virus through breastfeeding. Because of the benefits of breastfeeding, mothers are encouraged to breastfeed even in areas where Zika virus is found.

Through sexual contact

  • Zika virus can be spread by a man to his sex partners.
  • In known cases of sexual transmission, the men developed Zika virus symptoms. From these cases, we know the virus can be spread when the man has symptoms, before symptoms start and after symptoms resolve.
  • In one case, the virus was spread a few days before symptoms developed.
  • The virus is present in semen longer than in blood.

Through blood transfusion

  • As of February, 1, 2016, 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 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.

Risks

  • Anyone who lives in or travels to an area where Zika virus is found 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.
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