Of all the souvenirs people bring home from Brazil this year, dengue fever will no doubt be among the most memorable.

Of all the souvenirs people bring home from Brazil this year, dengue fever will no doubt be among the most memorable.

As I write this, Brazil is in the midst of a terrible outbreak of dengue fever. According to an article from the BBC that I read the other day, nearly a million people been affected. Although Brazil is having a genuine crisis, it’s merely one country where dengue fever is active. In 2014, some sources claim that there were probably over more than one hundred million new cases worldwide, with consistently rising numbers in India, China, and a number of other countries. In a time when more and more diseases are being contained and even eradicated, from a certain point of view, dengue fever is one of the most successful diseases on the planet.

Dengue fever is caused by a virus which spreads to humans via mosquito. The rapid rise in annual dengue infections is largely due to this vector. As cities spread, especially in developing nations, many animals and plants are wiped out, but mosquitos just settle in and adapt nicely, sometimes even doing better in a new environment devoid of predators. Slums provide plenty of standing water, which mosquitos need to breed, and endless places for them to hide, and there isn’t another animal in the world which will live in such unhealthily dense conditions as humans will.

When a person is infected with dengue virus, it takes about 2d8 days for symptoms to begin showing up. About 4 out of five of them will have no or minimal symptoms, usually a touch of fever, while people who become more severely sick develop gastrointestinal symptoms. In more severe cases, the first stage is an extremely high fever, which is accompanied by pain throughout the body, especially joint pain and headache. Most people will also develop a red, spotty rash. After 2d4 days, the fever usually breaks, but some people enter a dangerous phase, where the body’s coagulation system fails, leading to spontaneous bleeding, leakage of fluid out of blood vessels and into tissues (causing swelling and potentially filling the lungs), and dangerously low blood pressure that can lead to fainting, kidney failure, coma, or death. Finally, if the person survives 1d4 days of this, most people will begin to recover. Even this recovery is no fun, and can include a solid two weeks of fatigue, itchy rash, impaired level of consciousness, and seizures. All told, an infected human has about a 1% chance of death if they become infected (2-5% chance of developing the severe form, then 50% chance of surviving it) without modern medical treatment. A creature infected with dengue virus becomes immune to that virus, but there are five known strains of the virus and immunity to one doesn’t equal immunity to the others. What’s more, each infection seems to make the next one that much more severe (a phenomenon called “antibody-dependent enhancement”). We believe that most of the people who die are suffering from their second or later infection, not their first.

Interestingly, dengue fever is probably a relatively new disease. Unlike plagues like malaria or smallpox which predate recorded history, based on genetic evidence, the modern dengue virus is believed to have only evolved one to two hundred years ago, and one of the driving factors for this is quite likely humanity. Throughout much of the 19^th and 20^th centuries, large groups of humans migrated all across dengue’s prime territory – hot, damp, swampy or jungly regions – mostly while in the process of shooting each other. This ongoing influx of fresh, non-immune bodies, many of which were left to rot in swamps and fields rich in virus, would have been a perfect breeding ground for any virus and an optimal situation for a virus to adapt to make the best possible use of human hosts. Prior to this, records of dengue-like infections do crop up in texts dating back at least two thousand years, but it was probably very rare in humans. It’s hard to say this with certainty since dengue symptoms are generally non-specific and could have been various other infections.

So how did Brazil’s current outbreak happen? We’ll likely never know all of the thousands of variables that drive an outbreak, but one theory is that it’s actually due to a drought. With water levels looking like they were going to fall, households began to collect water in whatever containers they had to hand. What this amounted to was millions of pools of standing water all across populated areas, and thereby, countless pools of water right next to people’s homes, perfect for mosquitos. It just goes to show how unrelated events can be linked in unexpected ways.

Dengue fever may not have been a major problem in our medieval era, but that’s no reason why it couldn’t show up in a game. Dengue is an ideal choice of disease to have in any hot region, because it can be debilitating without having a high lethality. Dengue might be a new plague that healers can’t identify, or an old ague long known to a population. While it’s easily controlled with simple spells (cure spells, as well as any magic that repels insects), it could be used to lay low an entire party for a few critical days of game-time. Dengue virus might even be “farmed” by evil swamp-dwelling creatures, like a black dragon and its lizardfolk servants, as a way of keeping humans from penetrating too far into its territory, or with a tiny bit of magical tweaking, perhaps as a way of wiping out entire villages. 

More than four years ago, Dr. Eris Lis, M.D., began writing a series of brilliant and informative posts on RPGs through the eyes of a medical professional, and this is the one that appeared here on May 9, 2015. Lis is a physician, gamer, and author of the Skirmisher Publishing LLC OGL sourcebook Insults & Injuries, which is also available for the Pathfinder RPG system.