Transmission of Zika Virus

Through mosquito bites

Zika virus is transmitted to people primarily through the bite of an infected Aedes species mosquito (A. aegypti and A. 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. 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 mother already infected with 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 Zika virus to her fetus during pregnancy. We are studying the adverse pregnancy and infant outcomes associated with Zika virus infection during pregnancy.
• 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 likely sexual transmission, the men had Zika symptoms, but the virus can be transmitted before, during, and after symptoms develop.
• 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.

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.

Additional Resources

• MMWR: Transmission of Zika Virus Through Sexual Contact with Travelers to Areas of Ongoing Transmission — Continental United States, 2016
• Interim Guidelines for Prevention of Sexual Transmission of Zika Virus – United States, 2016
• Questions and Answers on Zika and Sexual Transmission
• Mosquito Life-Cycle
• Mosquitoes’ Main Aquatic Habitats