There is no feeling quite like finding a tick anchored to some forbidden region of your body. Am I going out on a limb here?
There are few things as disgusting as an engorged tick: that shiny grey satchel plump with your (or your dog's) dark blood; the pinpoint head; the short, curled legs; the awful lethargy.
Yet ticks fascinate as well as repel us. Having removed one, we examine it as it wriggles in the tweezers. We watch it sink to the bottom of the toilet. We make a big event out of putting the thing to death.
Dogs don't share this morbid response. A long-haired, outdoor dog, if he isn't looked after, can end up with a nasty collar of ticks by midsummer. But pull a tick off a dog's neck and he will only wag his tail and go about his business.
Ticks pass disease, but that doesn't account for our visceral reaction. We don't feel the same degree of loathing toward mosquitos or even lice, other critters that break the skin. Length of stay is what appalls us. That and the tenacity of a tick's grip.
Just how long will a tick stay, given its druthers? What happens when a tick is finally tanked up? Does it fall to the ground and just lie there, like an uncle after Thanksgiving dinner?
The answer is yes, sort of. Ticks move through stages: larva, nymph, adult. At each stage they hitch a ride and do the Dracula bit, after which they drop off the host and metamorphose. The female adult, sated, lays her scads of eggs and dies.
I learned all about the tick life cycle at a recent lunchtime lecture in the Agricultural Science and Industries Building. John Sauer, Regents professor and Sarkeys distinguished professor of entomology at Oklahoma State University, was the visiting speaker. Eastern Oklahoma, it seems, is, well, crawling with ticks, and there is a corresponding cluster of tick expertise. Sauer's specialty is the wide-ranging Lone Star tick, Ambylomma americanum, a variety that has been implicated in the spread of Lyme disease and Ehrlichiosis, an equally dangerous microbial infection.
A trim serious man, Sauer had come, however, not to damn A. americanum, but to praise him (and her). "Tough tenacious freeloaders," he called these little devils. How tough? A tick can last up to six years without feeding, possessing the ability to absorb water from the air. And anybody who's tried to kill one knows how resilient. "You can take a hammer to them," Sauer reminded, "and if they're unfed . . . "
As an arachnid physiologist, Sauer's main concern is, as he inevitably put it, "what makes a tick tick." Turns out it's got a lot to do with salivary glands.
A tick's salivary glands look like a cluster of grapes, and have some remarkable physical properties. Elasticity, for one thing: They swell by 25 percent when a tick is engorged, without any increase in the total number of cells. ("The change is unprecedented in cell biology," Sauer said. "I don't know why more people don't get interested in this tissue.")
Even more interesting, however, is what these glands secrete.
Put yourself in a tick's place. You haven't had a good blood meal in a couple of years. You've been waiting on your twig for what seems like forever, the sun on your back, ready to pounce on the first mammal that comes along. (You'll know it's a mammal by the smell of butyric acid it gives off—the same smell that emanates from rancid butter.) Comes a nice unsuspecting canine trotting by. At last! In a wink you drop to its back, burrow to skin, stick in the old proboscis.
What now? There are a number of challenges to be faced. You've got to make sure you're firmly attached, for one thing. You've got to get and keep that blood flow going. And then there are those pesky host defenses: the immune system, the inflammation response. . . .
None of this is going to be insurmountable, however; because you've got your saliva. Tick saliva is a real all-purpose biological fluid. It includes a kind of cement that helps with adhesion. It's got protein factors—anticoagulants, platelet-aggregate inhibitors—that pharmaceutical companies are starting to get excited about. And, says Sauer, it also has prostaglandin.
Prostaglandin is powerful stuff—a fatty acid derivative that acts like a hormone. Among its many known effects, it prevents clotting, dilates blood vessels, suppresses immune response, and douses inflammation. Voilá.
The curious thing, as Sauer found out, is that ticks can't make prostaglandin by themselves. Arachidonic acid, the necessary component, is beyond their capacity to synthesize. What they do instead, he found, is filter the acid from the incoming blood, and send it off to those grape-like salivary glands. There it is converted into prostaglandin, which is then secreted for use against the very host that, in a roundabout way, provided it.
This invertebrate ingenuity suggests a couple of things:
To Sauer, that finding a way to reduce the transfer of arachidonic acid—from livestock, for instance, via changes in diet—might be a way to control this troublesome parasite.
And to me, that in addition to loathing, the lowly tick deserves some respect.