An Anonymous Coward writes:
The Zika virus has been known for quite some time, but it gained notoriety recently due to its possible linkage to birth defects.
Science News has a summary report on Zika virus: https://www.sciencenews.org/article/special-report-heres-what-we-know-about-zika
A report on the studies of its possible linkage to microcephaly, a birth defect of babies with undersized and underdeveloped brains: https://www.sciencenews.org/article/how-zika-became-prime-suspect-microcephaly-mystery
In short, studies are continuing, evidence is mounting, but still not quite a confirmation.
That is just because hey are bad at their jobs. My experience was very similar to this:
For example, there have been many experiments running rats through all kinds of mazes, and so on—with little clear result. But in 1937 a man named Young did a very interesting one...He finally found that they could tell by the way the floor sounded when they ran over it...That is the experiment that makes rat‑running experiments sensible, because it uncovers the clues that the rat is really using—not what you think it’s using. And that is the experiment that tells exactly what conditions you have to use in order to be careful and control everything in an experiment with rat‑running...he subsequent experiment, and the one after that, never referred to Mr. Young. They never used any of his criteria of putting the corridor on sand, or being very careful. They just went right on running rats in the same old way, and paid no attention to the great discoveries of Mr. Young
People in these areas do NOT want to do the necessary work, they prefer to come up with excuses about how it is all "so complicated".
Infectious disease is easier to demonstrate than psychology studies.