The single biggest obstacle facing efforts to stop the Zika virus

The Zika virus, a mosquito-borne disease that has captured the world's attention after half a century of lurking in the shadows, is still relatively unknown to researchers.

Yes, there seems to be mounting evidence that the virus might be connected with a rare birth defect called microcephaly, in which babies are born with abnormally small heads. Researchers are also exploring the potential connection between Zika and Guillain-Barre Syndrome, a temporary disorder in which the immune system attacks part of the nervous system.

But despite these new discoveries, the lack of existing literature on Zika makes it hard for researchers to hit the ground running with the outbreak in the Americas.

On Friday, the head of the Centers for Disease Control and Prevention, Tom Frieden, tweeted a telling photo of a stack of all of the academic literature ever published on Zika. Here it is:

To give this some perspective, a quick search for "Zika" in PubMed, the medical library for the National Institutes of Health, comes back with 281 mention results. In comparison, a search for "Dengue," another mosquito-borne disease, turns up close to 15,000 results, and "influenza" comes back with just under 87,000. 

What we know

The Zika virus is a mosquito-borne disease (meaning it passes from person to person via mosquito bite) that was discovered in the 1940s. It wasn't until 2007, when the first outbreak of Zika occurred, that the virus was considered a major threat to public health.

Once infected, only about one in five people with Zika ever shows symptoms, which most commonly include fever, rash, joint pain, and red eyes.

Zika is carried by mosquitoes, namely the Aedes aegypti, a tropical bug that's great at transmitting diseases like yellow fever, dengue, and Zika. They are daytime mosquitoes, which means they bite during the day and like hanging out in warm, damp, heavily-populated locations.

What researchers are trying to find answers to

From a lack of ways to diagnose and treat Zika to equally tricky questions related to possible complications from the virus, it might be years until researchers can give answers to why the current outbreak is happening or what its true scope will be. And even the research that is coming out lately in response to the outbreak might not be as thorough as it could be.

We still need solid answers on the following topics, for example:

• The implications of sexually-transmitted Zika: Although the Zika virus is mostly transmitted via mosquito some rare cases of sexual transmission via semen have been documented in the past, and a person in Dallas, Texas recently got infected via sexual transmission. We know from academic reports that in December 2013, during a Zika outbreak in French Polynesia, a patient that was seeking treatment for hematospermia (blood in the semen) was found to have Zika in his semen. There's also a 2011 paper documents a man who unwittingly infected his wife with Zika after they had sex upon his return from Senegal where he was studying the mosquitoes responsible for Zika transmission.
• The link between Zika and microcephaly: Although it's looking more and more likely that there is a real connection here, there's still a lot more research needed before any causality can be proven. There were some cases reported in French Polynesia, but not to the magnitude of what's going on in the Americas.
• The link between Zika and Guillain-Barre Syndrome: While Colombia may be quick to say there's a "causal connection" between Zika, Guillain-Barre Syndrome, and three recent deaths in the country, this connection is still a major unknown. A quick search of PubMed turned up just one case report of an instance in which GBS occurred after Zika infection.

With any luck, Frieden's small stack of papers could multiply in the next few years.