The Zika virus is most often spread to a person through the bite of an infected mosquito. The mosquitoes that are known to carry the virus include two aedes species mosquitoes, which can be found throughout the world.
When a mosquito bites a person who is already infected with the Zika virus, the virus infects the mosquito. Then, when the infected mosquito bites another person, the virus enters that person's bloodstream and causes an infection.
During pregnancy, the Zika virus can also spread from a mother to the fetus.
The virus can also spread from one person to another through sexual contact. In some cases, people contract the virus through blood transfusion or organ donation.