I just noticed that this guest post of mine is no longer available on the original site, so I’m re-posting it here for any new Fallen World readers who missed it. 🙂

The idea of a mysterious sickness that no one knows how to cure is one of the scariest things I can imagine. When I started planning the book that would become The Way We Fall, I realized early on that I didn’t want to just gloss over the science with vague explanations. I wanted to understand the virus I was creating, so I could find believable ways to make it even scarier.

I read several books on viruses and disease, and talked with a microbiologist to make sure my ideas weren’t totally crazy. Much of my research didn’t go into the book–it just there in the background as I wrote. So I’m going to share with you here the factors I considered, and the reasons my virus acts the way it does.

Transmission

Viruses can pass from person to person in all sorts of ways. Pretty quickly, I decided mine was going to spread by respiratory means. That is, through the air: an infected person coughs or sneezes, releasing the virus into the air, where it can then be breathed in by another person, giving the virus a new home.

Why respiratory? Well, for my virus to be truly scary, it needed to spread quickly and easily, and airborne viruses are by far the most contagious. After all, you can catch them without even being that close to someone who’s infected. And all it takes is one cough and the virus can reach every other person in the same room. The only reason some of the world’s deadliest viruses, like Ebola, haven’t caused widespread outbreaks is that they can only be transmitted through direct physical contact with someone who’s already sick. Scientists who’ve seen hints that the virus may become airborne find the possibility terrifying.

Incubation

When you catch a virus, you don’t get sick immediately. There’s always an incubation period during which the virus starts to replicate itself in your body, before there’s enough of it to cause any symptoms. Some only take a day or two to emerge; some a week or more.

When creating my virus, I was inspired by measles. Measles spreads through the air, but it doesn’t give you the standard respiratory symptoms (coughing, sneezing) right away. It hides out in the body’s own cells, reproducing itself and gradually invading other systems, only provoking symptoms some ten days later. I gave my virus a similarly long incubation period, for a few reasons. Like measles, it doesn’t primarily infect the respiratory system–instead, its focus is the brain and nervous system, so I figured it would need some time to settle in there. Also, the longer it takes for people to realize they’re infected and start taking precautions, the easier it is for the virus to spread. And finally, for someone exposed to the virus, having to wait ten days to find out if they’re going to get sick is a lot scarier than only waiting two.

Symptoms

During my brainstorming, I sat down and made a list of all the possible symptoms a disease could cause, focusing on what seemed the most frightening, both to the person infected and to those witnessing it. More than anything, people seem to fear diseases that affect the mind. Consider the fact that it’s been years since the Mad Cow outbreak, and people still make nervous jokes about it. Who talks about SARS or H1N1 anymore? Look at the current fascination with zombie stories, in which the “disease” continues to control the behavior of the infected even after death. As uncomfortable as we are having our bodies turn against us, the thought of losing control over our minds is far more terrifying.

But zombie stories have always bothered me a little, because I find it hard to believe that the disease could take over nearly an entire civilization, when anyone infected is acting in ways that should make anyone not infected stay far far away from them. For a virus to have the best chance of passing through a population, I thought, it’d need to be doing something to attract new “victims” to it. Like the toxoplasmosis parasite which makes rats it infects less afraid of cats, so they’ll be more likely to get eaten and pass the parasite on to the preferred feline host.

So while the first symptoms that emerge when a character is infected with my virus seem like a typical respiratory infection–coughing, sneezing, fever–there’s also an itch. An itch caused by the virus tinkering with the nervous system. And before too long, the virus starts affecting the parts of the brain involved in inhibition and social desires. Those infected lose all sense of discretion at the same time as developing an intense longing for human company. If there’s no one around, they seek other people out, get as close to them as possible, and often pass the virus on.

If that were all, of course, it would be an embarrassing and uncomfortable sickness, but not all that scary. Which is why the virus doesn’t stop there. Since it was already attacking the brain, it made sense that as the disease got worse, people’s ability to process reality might break down completely, into delusions and hallucinations. And, in the end, almost all of them die. Like most of the diseases that frighten us the most–Mad Cow, Ebola–my virus has an incredibly high mortality rate.

One of the things that’s stuck with me after all my reading is how easily and quickly new viruses really can emerge–viruses we have no treatments and no vaccines for. I hope The Way We Fall works for readers who are looking to be scared, because I certainly have frightened myself.