Mosquito on Skin Flickr / John Tann

Until very recently, almost no one had heard of the Zika virus. The few familiar with the mosquito-borne illness didn't think they had any reason to be concerned by it.

Now, within the past few months, fears that the rapidly spreading illness could be responsible for a surge in infants born with microcephaly — a much smaller head and brain than normal — have prompted public health officials in Brazil, where there's a particularly serious Zika outbreak right now, to ask women to avoid getting pregnant. 

Zika hadn't appeared in the Americas until 2014, but it's now spread through South and Central America and into Mexico. As of December 31, it's also spread to the US, with a locally acquired infection reported in Puerto Rico.

An editorial in the January 9 issue of The Lancet journal calls Zika an emerging virus that poses a threat to global health security.

"Given that an outbreak anywhere is potentially a threat everywhere, now is the time to step up all efforts to prevent, detect, and respond to Zika virus," the editorial concludes.

There's still a lot that we don't know about Zika, including whether or not it's definitively the cause of infants being born with microcephaly or other neurological problems.

But this outbreak demonstrates clearly both the threat that emerging viruses pose to the world and the need to have some sort of antiviral agent that we can use to try to treat any new viral illness. While we can try throwing different antibiotics at any number of strange and unfamiliar bacterial infections, we have no similar sledgehammer for mysterious viral diseases, which each have to be studied carefully before we can even begin to figure out how to fight or prevent them.

Researchers have been trying to create a treatment that could be used for any type of virus for decades, and there are several promising possibilities in the works. Zika, the recent Ebola outbreak, and recent outbreaks of diseases like MERS and SARS show just how important and potentially lifesaving a treatment like that could be — and how frighteningly unprepared we are without one.

zika virus microcephaly Solange Ferreira bathes her son Jose Wesley, who was diagnosed with microcephaly, in a bucket of water, which she says he enjoys and helps calm him, at their home in Poco Fundo, Brazil. Ferreira was infected with Zika while pregnant. AP Photo/Felipe Dana

The problem of emerging viruses

Researchers discovered Zika by accident.

In 1947, scientists studying yellow fever put a rhesus monkey in a cage on a tree in Uganda's Zika Forest. The monkey came down with a fever, but the cause wasn't yellow fever: It was something the researchers had never seen before.

They named it after the forest.

A year later they realized that mosquitoes transmitted the virus — and that humans could catch it too.

Researchers eventually found evidence of Zika in Africa and Asia, and a Pacific Island outbreak in 2007 helped but it on the map.

At first, however, the illness seemed relatively mild. 

As a 2009 CDC document about Zika notes, we thought the same about West Nile virus — until we realized that it could cause serious neurological illness in a very small percentage of people infected with it.

Zika may turn out to be the same: a virus that has much more severe effects than we originally thought.

Dr. Michael Kurilla, director of the Office of Biodefense Research Resources and Translational Research at the NIH's National Institute of Allergy and Infectious Diseases (NIAID), recently told Tech Insider that for years, we thought certain viruses known as coronaviruses were relatively innocuous.

"But then SARS came around," he says, referring to the 2002-2003 outbreak of the coronavirus that infected more than 8,000 and killed approximately 10% of those infected.

mers saudi arabia camels mask contagious Camels seem to be a host for the MERS virus. Faisal Nasser / Reuters

Ten years later, we started to see MERS, another dangerous coronavirus, spread in the Middle East and eventually in South Korea.

"Within 10 years, there'll probably be another example," Kurilla says.

Viruses are, by their nature, unpredictable. They lurk in reservoirs all over the world, thriving in bats and rodents and monkeys. They mutate frequently when they replicate. Those changes can make a virus all of a sudden jump a species barrier to infect humans. A mutation can also make a mild virus turn deadly.

As journalist David Quammen explains in his book "Spillover: Animal Infections and the Next Human Pandemic," a deadly new virus will inevitably appear: "If you're a thriving population, living at high density but exposed to new bugs, it's just a matter of time until the [Next Big One] arrives."

A cure for all viruses

Since a new virus — or a mutated version of an existing one — can spread around the world before researchers have the chance to try and develop a way to treat it, something that could be used against any such infection would be an incredible tool.

These treatments, called "broad-spectrum antivirals," could be the biggest discovery in medicine since the invention of antibiotics.

ebola virus mre NIAID / Flickr

Tech Insider recently wrote the story of one man's quest to create an antiviral agent that might be able to fight a broad range of viruses, but the scientist behind that project, Todd Rider, is struggling to raise the money needed to study whether his cure works or not.

Rider's potential cure, DRACO, has not been tested against Zika, but it did show effectiveness against the related Dengue virus in cell tests. Still, such early experiments are a long way from testing to see whether it could safely cure a virus in humans.

DRACO is less proven and less developed than some other broad-spectrum antivirals. An interferon compound, for example, is based on something our body naturally produces; it's already been used to treat hepatitis C. That compound has also been tested in humans against SARS, certain influenza viruses, and Ebola.

Still, no broad-spectrum antiviral is widely used yet. We have nothing we can reliably throw at any new, emerging viral threat — and there are bound to be more.

Some promising antivirals have failed when they've been tested in humans; others have painful and risky side effects. Even with effective treatments, Kurilla says that medical experts are cautious about using them because they're concerned that viruses could mutate to become resistant to the antiviral, making them potentially useless at some future moment when they may be most needed.

But the threat posed by viruses is always out there. There are approximately 320,000 mammalian viruses, according to a recent estimate. If even just a fraction of those can infect humans, those are thousands of reasons to further the research working toward developing effective broad-spectrum antivirals.