As much as we can decry media sensationalism, Zika is set to be the next Ebola. The health organisations have convened emergency committees, the WHO have declared a state of emergency, and the virus is rippling throughout South America. Brazil alone have reported around 1.5 million cases in the last year although even the authorities are saying that’s only guesswork at this point.

Courtesy of the CDC

Though the Zika virus is not a new disease, having been first discovered in 1947, it has broken onto the world stage after appearing in April 2015 in Brazil. In contrast to Ebola, what makes Zika so frightening isn’t its high mortality rate, in fact 60-80% of cases experience no symptoms. What makes it so terrifying is its ability to spread rapidly and the growing links to microcephaly, the full extent of which we are only beginning to understand.

Zika is yet another of the diseases spread by mosquitoes, making them the biggest killer of humans at roughly 750,000 per year, mostly via malaria. Currently most cases are thought to be due to Aedes aegypti (seen in pink) and looking at this map of occurrence in 2013-2014, it’s easy to see why Brazil is the most hit.

Kraemer MUG, Sinka ME, Duda KA, Mylne A, Shearer FM, Brady OJ, Messina JP, Barker CM, Moore CG, Carvalho RG, Coelho GE, Van Bortel W, Hendrickx G, Schaffner F, Wint GRW, Elyazar IRF, Teng H, Hay SI (2015) The global compendium of Aedes aegypti and Ae. albopictus occurrence. Scientific Data 2(7): 150035. http://dx.doi.org/10.1038/sdata.2015.35

Current estimates already peg Zika as likely to spread throughout the Americas due to the high levels of its main mosquito vector, compounded by the way it normally bites during the day, making the trusty bed-net much less effective. One fear is that Aedes albopictus (seen in red) might also become a common vector, suddenly putting a much larger population at risk. Such is Zika’s talent for infection, the first case of sexually-transmitted Zika virus has been discovered in the US.

So we’ve established that it can spread rapidly, but if it doesn’t kill many or cause many symptoms why should we worry? Well there is a growing body of evidence linking maternal Zika infection with microcephaly and Guillian-Barre syndrome. Microcephaly is a condition of abnormally small head diameter, normally indicating neurological deficits, and usually affected children have a reduced life expectancy and have a poor prognosis for brain function.

Until this last year this link was unknown, and there is no known treatment or vaccine for Zika. Such is the fright that health officials in Brazil are urging women not to get pregnant, and women world-wide who are thinking of having children are being warned against attending the Rio Olympics later this year.

Furthermore abortion is still illegal in Brazil, even in cases where microcephaly has been diagnosed, thus the burden is likely to fall square on the women of Brazil, and on the Brazilian health services. So far one of the only legal justifications for abortion in Brazil is in cases of anencephaly, a more severe version of microcephaly, and that was only granted after a long court battle in the Brazilian Supreme Court.

All told the outlook is looking pretty bleak right now. The WHO are estimating another 3-4 million cases in the next year, all while incidence of microcephaly and other complications are relatively unknown. Whatever the progression on vaccines and treatments, many thousands ae still likely to suffer.