7 p.m. December 27, 2012

The Science Of Christmas (Pt. II): Reindeer Will Have Your Eye Out

In a rather festive correspondence from the New England Journal of Medicine, a team of physicians reported on five cases of Dermal Swellings and Ocular Injury after Exposure to Reindeer.

Anyone fancy a guess as to what caused the injuries in the cases described? Head butt? Accidental face-to-antler altercation? Rudolph’s shiny, red nose causing temporary blindness leading to face-planting on the cold, arctic tundra?

The answer, my holiday readership, is so much more than a black eye from a cantankerous caribou. So clutch your cocoa, snuggle up in front of the fireplace, and grab your eye bleach because it’s time to talk about myiasis.

The NEJM correspondence describes myiasis in five children who had visited reindeer herding grounds during the summer. The children all had migratory dermal swellings that appeared after their exposure to the reindeer. Diagnosis of myiasis was confirmed via a single larva extracted from an eye of each child.

What’s myiasis? Glad you asked. Myiasis is the infection of tissue by fly larvae. The children were infected with Hypoderma tarandi, a parasite that lays its eggs on reindeer, and whose larvae burrow through Dasher and Prancer’s subcutaneous layer and feast upon reindeer hide for the duration of winter. The children had maggots growing and crawling around in their faces and they got them from reindeer. Welcome to your Christmas nightmare.

H. tarandi belongs to the Oestroidea, a family of highly specialized flies, often referred to as bot flies. “As adults, many of them resemble large, adorable, fuzzy bumblebees,” writes Peter Coffey, researcher at the University of Maryland College Park and oestrid enthusiast. “With their big eyes, and tiny vestigial mouths they almost look like cartoon characters. However, they're known more for their larvae, which have the particularly endearing habit of developing in the skin of mammals.”

Adorable.

“A female bot fly might lay eggs in an animal den, in soil, on clothing, on animal skin, or even on a captured blood drinking insect which would then transfer the eggs during their next blood meal.” In the case of H. tarandi, the mated females oviposit their eggs on the guard hairs in the coat of the caribou. Once the eggs hatch, the maggots crawl down the hair’s shaft and penetrate the skin, burrowing into the host’s subcutaneous layer. And then they migrate.

The H. tarandi larvae wriggle their way to the dorsal flank of the reindeer, poke a hole in the skin for breathing, and get comfy for nine to eleven months, at which point they squirt through their airhole and plop onto the ground where they metamorphose inside a pupal case. But how do oestrid larvae know where to migrate once inside a reindeer? “The general consensus is that the larvae follow along the threads of fascia, or connective tissue, until they reach their destination.” Their destination, in this case, being the animal’s back. You know, a place where their host can’t easily reach. A place for the larvae to hang out en masse while they eat and breathe and chill with their 200 to 2000 fat, inch-long maggoty friends.

Wondering how these juicy larvae breathe while face down in reindeer flesh, noshing away? (You probably weren’t but I’m going to tell you anyway.) Three sexy words: anal breathing apparatus. “Insects have a simple respiratory system which consists essentially of tubes, leading from the outside of the body to wherever oxygen is needed. So this breathing apparatus is essentially an extension of that tube which reaches out of the host body so that the fly can taste fresh air.” Oh, delicious. “Picture it as a snorkel sticking directly into your heart, supplying oxygen without all that pesky breathing, so convenient!”

But how, how does an oestrid larvae hang out in the living flesh of it’s host without repercussions, for as long as it takes them to get fat and happy? “It's incredibly risky for any parasite, because they're constantly in almost impossibly hostile environment. They're constantly surrounded by an environment which wants to kill them by any means necessary, but the benefits are incredible.” Benefits, you say? “They're constantly surrounded by a warm house made of fresh food which transports them to new exciting places. It's too tempting to pass up for thousands of species.”

So, to keep from getting killed, the larvae do what they can to be nice house guests. “Since the larvae lives in what is sometimes essentially an open wound they often secrete antibiotics to keep down the risk of infection.” This may seem like a sweet thing to do, but that larva needs the host to stay alive. If the host dies, that squidgy, pale fly baby goes with it.

Lest you have been comforting yourself with thoughts that the subartic H. tarandi are far away, it’s time for a reality check. Myiasis is super common. “[Myiasis] can be incredibly complicated to talk about because there are so many different species of flies which infect a large variety of species and tissues to varying degrees, and with a wide range of effects on the flesh owners.” And with all the available meat and warmth that billions of available humans provide, you can bet your sweet, delicious ass that there are bot flies out there that would love to get a taste. “Bot flies are probably more generalists than most. The most common hosts for the human bot fly, Dermatobia hominis, are actually cattle and dogs, hardly closely related species.”

Oh, and did I mention that they have backwards facing hooks on their pulpous white bodies such that they cannot be easily pulled out of their cozy abode? Because they do. Those little fuckers are squished in there good and tight.

Merry Christmas!

[Note: Subscribers, you are in for a treat! My entire correspondence with Coffey is up in Desknotes. He’s brilliant and I would be remiss if I didn’t compel you to stroll on over for a holiday lesson in parasitology]

Back channel chatter

There is a scribble about this dispatch in the backroom, with two contributors.