By Gustav Omar
Few creatures, except perhaps the armadillo or the wild turkey, are as emblematic of the New World as the rattlesnake. Before Columbus s voyage, Europeans had never seen one. Rattlers are not found in Europe, Africa, or Asia, but almost every state in the Union (Maine, Alaska, Hawaii, and Delaware are the exceptions) has at least one species. Arizona boasts eleven. A total of seventy species and subspecies–ranging from gigantic diamondbacks, which may exceed seven feet, to an eighteen-inch subspecies native to only a few mountains in Arizona–are found in North, Central, and South America.
The most distinctive feature of this reptile, of course, is its rattle, made of two to ten hollow interlocking segments of a light, fingernail-like material. When the rattlesnake vibrates its muscular tail, each separate segment bounces against the adjoining ones at fifty cycles per second, creating a buzzing sound that signals sensible folks to stay away. Unfortunately, not everyone does.
Most rattlesnakes are peaceable, retiring animals that flee for the underbrush when they encounter humans. Unless they are hunting rodents, rattlers strike only in self-defense. But if you step on one or try to capture it, a rattler will retaliate with a rapid strike that can be debilitating or even lethal. In the United States, about 8,000 people a year are bitten by rattlers or their cousins in the pit viper subfamily, which includes copperheads and water moccasins. In 1988 two doctors at the University of Southern California Medical Center analyzed 227 cases of venomous snakebite, covering more than a decade, and found that 44 percent occurred during accidental contact, such as stepping on the animal. More than 55 percent, however, resulted from the victim’s grabbing or handling the creatures, and in 28 percent of these cases, the victims were intoxicated. The doctors’ conclusion was that the typical snakebite victim is male and under thirty, with a blood-alcohol concentration of more than 0.1 percent at the time he is bitten. Yet only 0.2 percent of all snakebite victims die each year, and most of them receive no medical treatment or first aid.
Rattlesnake venom is not a simple poison. The snake’s venom glands; located at the rear of the upper jaw and connected by ducts to its pair of hollow fangs, produce a complex brew of toxic peptides, polypeptides, and enzymes. In the venom, these toxins are combined in differing proportions that vary throughout a species’ range and even during an individual snake’s lifetime. Rattlesnakes harbor so many biochemical mixtures for venom that toxinologists who analyze the stuff confront a range of variations rather than a standard formula for each species. Some of this variability seems to reflect recent changes in the venom of certain rattlesnakes, from the hemotoxic and proteolytic type (which affects blood and other tissues) to the neurotoxic type (which attacks the nervous system). The first type hasn’t changed into the second; rather, the proportion of neurotoxins in the mix appears to have increased in some areas of the country. Consequently, victims may now receive a significant dose of both types of poison from a single bite.
Matters seemed a bit simpler a few decades ago. Scientists knew that pit vipers produced a hemotoxic venom that was rarely deadly to humans. Except in Arizona and parts of Texas and California–home to the deadly, neurotoxic Mojave rattlesnake–most humans bitten in the United States could expect to survive. But they did experience depressed blood pressure associated with shock, destruction of tissue near the bite, massive swelling of the affected area, and hemorrhaging both near the bite and internally (caused by anticoagulants in the venom). If untreated, the area around the bite would become gangrenous and turn black. Sometimes the venom would also attack the kidneys. People lost fingers or toes, but few died–particularly after the introduction in the 1930s of an antivenom made from horse serum. In the worst cases, a bite victim usually had an hour or two to get to a hospital before the situation turned dire.
Neurotoxic venom, on the other hand, doesn’t allow for such leisure, because it blocks nerve impulses to muscles, including those in the diaphragm that are used in breathing. Usually associated with members of the cobra family, a neurotoxic bite can cause immediate, shortness of breath, weakness or paralysis of the lower limbs, double vision, inability to speak or swallow, drooping eyelids, and involuntary tremors of the facial muscles. Death can occur in as little as ten minutes, usually due to abrupt cessation of respiration. In the 1970s, researchers at the Veterans Administration Hospital in Salt Lake City, Utah, identified the Mojave toxin that makes this little reptile the most deadly rattler in the United States–even when its victims have been treated with antivenom.
Over the past few years, however, neurotoxic symptoms have appeared in several people who apparently were bitten by other species of rattler. In 1999 in Hesperia, California, an eighteen-year-old reptile hobbyist received a bite on the hand while trying to grab a local rattlesnake with his bare hands. The species was believed to be a southern Pacific rattlesnake, a subspecies of the prairie, or western, rattler. Within minutes, the young man developed general weakness, had difficulty breathing, and showed the classic neurotoxic symptoms of double vision, facial twitches, and an inability to swallow or talk. He recovered only after being treated with thirty-five vials of antivenom. The doctors who treated him, Sean Bush and Eric Siedenburg, of the Loma Linda University Medical Center, published a report of the episode, calling it the first known case of neurotoxicity associated with a suspected southern Pacific rattlesnake envenomation. Yet the victim also showed several classic symptoms of hemotoxic poisoning, such as hemorrhaging and swelling of the hand and arm. The doctors observed that even if the snake had been misidentified and was really a Mojave rattlesnake, the case would still be noteworthy "because envenomation demonstrating both venom A [neurotoxic] and venom B [hemotoxic] effects has not been reported previously from southern California."
