Like the West Nile virus and dengue fever, the primary carrier of the Zika virus is a mosquito. In particular, the mosquito that carries Zika is of the Aedes variety—primarily the Aedes aegypti mosquito that is also the main carrier of dengue fever. The full list of vectors is not completely known, but the virus has also been isolated in a few other species of mosquito.

Humans are also carriers, as the virus can possibly be transmitted through sexual intercourse. An infected mother can also spread the virus to the fetus.

The Zika virus may have only filtered into the mainstream consciousness in the several months since the outbreak, but it was not discovered recently. It was first isolated by scientists in 1947, and it wasn't until 1952 that we had the first evidence of infection in a human. In Nigeria tests, 50 out of 84 people across various ages showed antibodies to the virus; in India tests, a significant number showed an immune response to the virus. These findings suggest that the virus had been widespread in humans for a long time already.

The first outbreak that occurred outside of Asia and Africa was in 2007, in the island of Yap in Micronesia. In 2013-14, an outbreak also occurred in Oceania, spanning the Cook Islands, Easter Island, French Polynesia, and New Caledonia. Then we have the well-documented outbreaks in late 2015 through early 2016 in the Americas.

This fact has only been truly confirmed recently, but now there is no more doubt that this virus will cause microcephaly in newborn babies whose mother had been infected during pregnancy. It is not yet clear whether the pregnancy stage at the time of infection affects the outcome.

At the moment, there exists no vaccine to counter this virus. Scientists are hard at work trying to come up with various solutions, though, so there should be more progress sooner rather than later.