Cheshire

Here’s an interesting story out of Florida…it seems they have a widespread outbreak of Dengue fever.

Dengue is an interesting virus…it’s an arbovirus, which means it’s a virus spread by arthropods. In this case, it’s a mosquito.

So…let’s talk about Dengue.

What is it, what vectors it, how does it reproduce inside the vector and what can we do to control the vectors?

Dengue is a type of RNA virus called a Flavivirus. Instead of DNA, it’s genome uses RNA which is directly translated into proteins.There are four different types of dengue, but all of them have the same symptoms. You get sick with one, and you feel like you’re being ground into a pulp…it’s also known as break-bone fever. Get another serotype, your immune system attacks itself, causing you to bleed from every orifice of your body. This virus is really bad news. Even worse, this virus uses mosquitoes to spread. Mosquitoes are everywhere here in Iowa, and they’re probably not much better in Florida.

Interestingly, Aedes albopictus outcompetes Aedes aegypti wherever it’s established, and this mosquito ranges up to at least New Jersey. Even scarier…the mosquitoes which vector this virus feed mainly on people.

There are two main vectors of dengue in Florida…Aedes albopictus and Aedes aegypti. Both of these mosquitoes are very well adapted to living around humans. It’s their home turf. Their native environment. They’re damn good at globehopping, too. Better than say…Anopheles gambiae

Aedes aegypti and albopictus are spread throughout the world by transport ships. Let’s say that a transport ship docks in Africa during a rainstorm and some Aedes and Anopheles chicks drop by and lay their eggs. The Aedes girl will lay her eggs slightly above the water line, while the Anopheles girl will lay her eggs in the water.

The puddle (in…say, a tire) dries out, and the Anopheles larvae die. No big deal, right? The world will go on. Those Aedes eggs are still ominously clinging to the sides, though.

The ship docks. The tires are unloaded in Florida. It rains. The tires fill up, and now those Aedes eggs hatch. And that’s the problem with controlling these mosquitoes. Their eggs are essentially indestructable and can keep for nearly half a decade. Even in areas of Texas that are prone to drought, you can still get these mosquitoes despite the fact they need water to reproduce.

And that’s the other thing about mosquitoes. They’re the Buffy Summers of water-finding.

If you’re a fan of Buffy the Vampire Slayer, remember how she always used to find a stake wherever she needed it?

Well, mosquitoes are that way with water. They’ll breed in toys, flowerpots and Starbucks cups if given the chance. In a weird way…litter can kill. Kind of.

Anyways…the interesting thing about this virus is that it doesn’t get the mosquito sick. They actually regulate the virus’s reproduction somewhat well in their system. It enters the mosquito through a bloodmeal, infects their midgut (their esophagous and foregut is protected by a thick layer of exoskeleton) and eventually goes systemic. The virus enters the mosquito’s salivary glands and is passed through a bloodmeal.

Arthropod borne diseases are controlled through vector control. The idea is to get the vector populations down enough to make finding viremic hosts unlikely. A lot of this is done by spraying for adults, or by putting a special version of BT in water containing mosquitoes which will poke holes in their guts (same species used in corn, different strain). You can also destroy mosquito breeding grounds by keeping your devoid of any containers. Problem is, with the ability of the Aedes eggs to survive adverse conditions this makes simple mechanical control very tricky.

So if you live in Florida, slather on the DEET and clean your yard.