23 Jun 2018

Snake Bit in Yosemite

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Northern Pacific Rattlesnake (Crotalus oreganus).

Kyle Dickman was bitten in the ankle by a rattlesnake in Yosemite Park.

The impact of the snakebite and his rescue make for quite a story. As does the analysis of what the snake’s venom did, supplied by a biochemist expert from the University of Northern Colorado.

Snake venom contains a suite of proteins that dock perfectly with the cells and proteins humans use to regulate our respiratory, vascular, and digestive systems. Except that when the venom proteins dock, it’s sabotage. “Mammals operate within very narrow parameters,” Mackessy explains. “We don’t tolerate big swings to our heart rate, -temperature, or blood pressure. Venom is like a shotgun blast to the intricate inner workings of a watch.”

Mackessy calls venom’s ability to affect so many different life functions a product of “evolutionary warfare.” He points to a dead fence lizard stuffed into a vial in his lab. This species of lizard, which came from a sky-island mountain range in Arizona, has developed resistance to the venom of the rattlesnakes that prey on it; however, over time and through evolution, the rattlesnakes are also adapting, developing proteins to sidestep the lizard’s defenses. This one-upmanship between predator and prey explains why venoms, and the actual mechanism they use to kill or harm, vary not only between species of rattlesnakes but also within populations of the same species. One example of this hyperspecialization can be seen in the southern Pacific rattlesnake, which claims the bottom half of California as its territory. One researcher recently discovered that a bite from a Pacific rattlesnake near sea level in San Bernadino County prevents a victim’s blood from clotting. But get bitten by the same species in the mountains of the same county and your blood will clot.

Snakes brew their venom in glands located behind the eyes. In a snake’s lifetime, these glands can weaponize—or attempt to weaponize—many proteins that have alternative functions in its own body. One that digests food may be tweaked to break down living prey. Or a protein that increases the snake’s blood pressure could be altered to decrease that of its meal. For a sense of just how sophisticated and varied venom is, consider that all 300 of the world’s venomous snake species have been fine-tuning their toxins for millennia. In the venom of the rattlesnake species that bit me, a northern Pacific, more than 75 proteins have been identified—and Mackessy thinks many more may yet be discovered.

We’re now in his office, where mason jars filled with rattlesnakes coiled in alcohol line the shelves. Mackessy says he’s hesitant to describe what any one venom protein did to my body, because it’s like describing the role a single note plays in a sonata. It tells an incomplete story. Proteins work in concert.

Caveats aside, Mackessy starts with my first symptom: fainting. The body regulates blood pressure through proteins that cause veins and arteries to expand or contract. Northern Pacific rattlesnake venom contains a protein that functions identically. Within moments of getting struck, Mackessy explains, the venom “rapidly and inappropriately” relaxed the vessels that regulate blood flow. “Blood pressure went like this,” Mackessy says, whistling and sliding his hand down an imaginary slope.

My body tried to correct this by flooding my vasculature with a protein that constricts blood vessels. And here’s where venom gets particularly nasty. The same venom protein that caused my blood pressure to drop also destroyed my body’s tools for increasing it. “That’s just one thing—one component in one venom,” Mackessy says.

While I was passed out, he goes on, an enzyme called metalloproteinase broke down my leg veins’ walls until I began to hemorrhage internally. Meanwhile another venom protein, disintegrin, acted as a magnet to my platelets and fibrinogen, molecular components that help blood clot. As my body sent them racing to plug the puncture wounds, the snake protein destroyed them, like a host who throws a house party and clubs guests the moment they arrive. Welcome!

Mackessy describes a toxin that made my smooth muscles—those in my digestive tract—convulse, pushing my stomach’s contents out both ends. Another liquefied the cellular architecture in my leg, releasing fluid that led to elephantine swelling while simultaneously quickening the venom’s spread upward by turning flesh, as he describes it, into “diluted Jell-O.” Still another digested my muscle tissue. He shows me a picture of an untreated snakebite case taken nine days after the strike. The victim’s foot is a mess of exposed bones.

In my case, all these processes happened almost instantaneously because the rattlesnake’s fang hit a vein.

RTWT

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