How the Zika virus spreads

The major source of Zika viral transmission is most likely via mosquitoes

Zika virus is transmitted to people primarily through the bite of an infected Aedes species mosquito (A. aegypti and A. albopictus, potentially also Culex sp.). A. Aegypti and A. Albopictus 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. 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.

Zika can also spread though 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.

• The length of time that Zika remains at high levels in semen is currently unknown.

The Zika virus can spread from a pregnant woman to her child

A mother already infected with the Zika virus near the time of delivery can pass on the virus to her newborn around the time of birth.

A pregnant woman can pass the Zika virus to her unborn child during pregnancy. There are adverse pregnancy and infant outcomes associated with a Zika viral infection during pregnancy.

To date, there are no reports of infants getting the Zika virus through breastfeeding. Because of breastfeeding benefits, mothers are encouraged to breastfeed even in areas where the Zika virus is present.

As of February, 1, 2016, there have not been any confirmed blood transfusion transmission cases in the United States.

There have, however, 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.


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