What the Dengue Fever Outbreak in Honduras Portends for the US

Cases of dengue fever have increased 30-fold in the last half century, the WHO says, calling it the most important mosquito-borne viral illness in the world. Nowhere is this more palpable than in Honduras, which has declared a national state of emergency as a dengue epidemic grips the country.

With the mosquito capable of carrying dengue now established in over half the United States, is this something the nation ought to be wary of as the climate continues to change, and our populous cities become ever more viable breeding grounds for the loathsome tiger mosquito?

Before we get to the answer—which is more complex than it may seem at first—let's look at Honduras: Fearing a repeat of the dengue epidemic of 2010, the Honduran government has declared a state of emergency after 12,000 people have been diagnosed with dengue, including 1,800 cases where there's a risk of dengue hemorrhagic fever. Half of the nation has reported cases of the disease.

The regular variety of dengue is bad enough, characterized by high fever and illness accompanied by severe joint pain, but dengue hemorrhagic fever is deadly, preceded by internal bleeding and all sorts of nastiness.

Globally there are roughly 100 million dengue infections each year, in 100 nations, with 40 percent of the world's population at risk. If treatment is available, the death rate is just 1 percent, but untreated, severe dengue can have mortality rates over 20 percent.

Since World War II and the push to eliminate malaria in America–which also slayed the mosquitos that carry dengue–the vast majority locally-caught cases of dengue in the US either occurred in border areas of Texas, in Hawaii, or in Puerto Rico (where it was never eliminated). In recent years however, locally-caught cases have been on the rise in the continental US. Nothing dramatic in numbers, but enough that officials have said that dengue is re-established in the Florida Keys.

That said, according to data compiled by the USGS as of the end of last month, outside of Puerto Rico, there have been exactly zero cases of locally-caught dengue in the nation—which is no doubt cold comfort to the residents of Puerto Rico, where there are currently 3,655 cases of the disease.

How this could change in coming years has been modeled in a bit more detail, and more recently than NRDC did in the report from which I grabbed that map above, by researchers from Texas Tech University. Looking at how dengue could spread as the climate warms in the coming years and decades, they discovered that infections in the US could occur in somewhat counterintuitive ways.

Rather than simply following the spread of the mosquitos as regions become more hospitable to them throughout the year, what we could see is that outbreaks of dengue in more northern areas such as Chicago could actually be more severe, coming largely in the summer, than those in southern places like Georgia and Texas, where dengue could become a disease of the spring and fall.

How to combat it, beyond the most basic step of eliminating likely breeding areas for mosquitos in inhabited areas?

As it stands, there's no vaccine for dengue, though one being developed by Sanofi-Pasteur and being tested in the Philippines may be released for public use soon. Interesting work is being done in Sweden that claims to be able to predict when dengue outbreaks could occur, with a four-month lead time, thereby giving local government and medical facilities time to prepare for a influx of patients.

There are also efforts to develop genetically-modified mosquitos to combat dengue—including some frankly rather sketchily-communicated field trials in the Cayman Islands wherein the local people weren't notified that testing was going on. Call me cynical if you like, but unleashing mutant mosquitos on an unsuspecting populous falls into the category I like to call, 'Hell, what could go wrong?'

The state of emergency in Honduras should send a chill over the warming planet. Even though Honduras has had a dengue outbreak before, in 2011 it didn't have any reported cases. This is either a sign that the measures taken after the 2010 outbreak were effective–or a sign that even the seemingly safe need to watch what bites them.