Monday, November 23, 2009

This Month's Sci-Fi Worthy Parasite: Dermatobia hominis

Mosquitoes carry a lot of parasites, many of which are global health concerns. Mosquito vectored diseases include protozoan diseases like malaria, filarial diseases, and viruses like dengue fever, encephalitis, West Nile and yellow fever. Perhaps the least-concerning creature you can get from a mosquito is Dermatobia hominis. But what it lacks in deadliness it makes up for in grossness.

Dermatobia hominis , or the human botfly, is a fairly common looking species of fly native to Mexico and Central America. From its outer appearances, you wouldn't think anything bad of it. Like other flies, the botfly has a simple life cycle; eggs that turn into maggots, maggots which grow then pupate, transforming into a fly. Most maggots feed on necrotic or decomposing tissues, hence their common appearance on corpses or other dead creatures. The botfly, however, takes its own spin on things. Its young need to eat healthy flesh to survive. Living in healthy tissues means that the larvae are protected from other creatures and the harsh world outside.

And, of course, being the human botfly, Dermatobia hominis maggots feed on our flesh, specifically. The subcutaneous (below the skin) layers of our bodies turn out to be magnificent nurseries for larval flies. It takes a larval botfly about eight weeks to grow and mature while dining on our tissues, then they crawl out and pupate in the soil. Around a week later, a small, gray adult fly emerges.

The trouble with using a human host for your eggs, though, is that it's not really a good idea to put hundreds of maggots in the same area like other flies do in decomposing flesh. That many larvae might damage the host a lot, causing the wound site to get infected. This is bad news for the botfly - infections are fatal. Since the fly larvae can only survive the entire eight-week development if the wound does not become infected, it's important for the flies to deliver only a very small number of larvae to each host, preferably one at a time in a given spot.

That's where mosquitoes come in. Dermatobia females use mosquitoes to deliver their eggs to viable sources. By using a vector like the mosquito, the flies not only deliver fewer eggs per host, they disperse to wider ranges and more hosts than they could on their own. Botfly eggs are transported by at least 40 species of mosquitoes and flies, as well as one species of tick. The female fly captures the bug and attaches her eggs to its body using a specialized glue which is melted by our body heat when the mosquito lands. The eggs then fall off the mosquito while its feeding and hatch. Botfly eggs react to the change in temperature as a signal to dig in, burying themselves under our skin.

We start to notice that a botfly larvae is growing in us because bite wounds get a little larger and more persistent then normal. As the fly larva grows, it can become visible, even be felt and seen moving around beneath the skin. The easiest way to deal with a botfly is to get it surgically removed by a doctor. However, the larvae breathe through small openings in the skin, and covering these tiny holes can coax them to leave the host on their own. Those who don't want to pay for an office visit often use bacon fat, petroleum jelly, or even nail polish to suffocate the larvae, which then move to the surface to breathe and can be removed by hand.

Here's a little video of this:

If you really want to gross yourself out, here's one being removed from someone's eyelid:

Anyhow, as you can see, while they may not be as deadly as some of the other mosquito-borne diseases, they are definitely far more disgusting. It's just like the plot of a science fiction book; a creature burrows into our bodies, consuming our flesh and blood for its sustenance before bursting out in dramatic fashion. For their creepy use of our flesh as maggot nurseries, botflies definitely are sci-fi worthy. Tune in next month for another disturbing, disgusting, and otherwise amazing parasite!


Gini said...

Yaaaaakkk! I was super paranoid about botflies when we went to Belize and Guatemala this summer. Fortunately I was lucky enough to avoid being taken hostage by one.

Julia said...

Dear LORD. That "Botfly in my Head" video is truly, delightfully gag-arrific!

yud said...

Botflies aren't only a tropical parasite. I live in central Virginia, and this last summer we found four botfly larva in one of my little dogs.

Joshua said...

Very gross and very neat. I was vaguely aware of bot flies but I didn't know that they used mosquitoes as an intermediary. That's really cool. There's a temptation to make a joke that this is so gross that it is evidence against evolution since such extreme grossness could not arise naturally. Obviously there is a Designer and the Designer has the humor of a 14 year old boy.