Natural Resistance to Snakebite
Having lived on Hacienda Barú with its extensive rainforest for more than 50 years, I have seen numerous animals suffer the effects of snakebite. These include dogs, cows, horses, pigs, and people. Since by far the most common venomous snake in this area is a pit viper known locally as the terciopelo (Bothrops asper) we always assume that it is the species of serpent that bit the animal. On average I see three venomous snakes annually, about 150 during my lifetime. Most of these were on the trails of Hacienda Barú, three in the stable, and one in the house. I see a corral snake about once every decade, and I have seen two black-headed bushmasters in 50 years. The others have all been terciopelos.
The people I know who have been bitten received proper treatment in a hospital with antivenin, some very soon after the bite and some up to eight hours later. All survived and the one who didn’t receive the antivenin until eight hours later had to have his arm amputated. Most suffered some tissue damage, at least an ugly scar, in the area around the bite, and a few had recurring problems, such as swelling and oozing of pus from pores, for years. I imagine that people have very little if any natural resistance to snakebite.
I have seen around a dozen snake-bitten cows, three of which survived without treatment. Those three were bitten on the foot or lower leg. Those who were bitten on the nose while they were grazing all died, but usually not until a day later.
Horses have very little resistance to pit viper venom and die soon after being bitten. I don’t know of a single horse that has survived a snakebite.
Neighbors who have pigs tell me that a pig that is bitten by a venomous snake will more than likely survive. A friend saw a terciopelo bite one of his best pigs, and it didn’t show any symptoms at all. Fatter pigs have more resistance than skinny ones. Fat has very few blood vessels. Another advantage of pigs is their thick skin which is hard for the snake’s fangs to penetrate. After doing a little research on the web, I discovered that pigs also have a genetic mutation that makes them specifically resistant to a toxic substance called a-neurotoxin found in pit viper venom.
I have never seen a snakebitten opossum, but it is well known that they are extremely resistant to snake bites. Scientists have discovered a protein in opossum blood called Lys49-phospholipase A2 (Lys49-PLA2) which they believe gives the opossum its strong resistance to pit viper venom. There is hope that this protein can be synthesized and used as an antivenom by humans.
One of our dogs was bitten on top of his head. Within a couple of hours, his head swelled to three times its normal size. He laid on a blanket on the floor and wouldn’t eat, only sipped a little water. Every time we went into his room, we expected to find him dead. After four days, the swelling slowly diminished, and he started eating. A large pocket of pus formed on top of his head in the area around the fang marks. We treated it by squeezing the pus out daily and injecting antibiotic creme directly into the empty pocket which eventually healed. That was back in the days when the roads were horrible and there were no veterinarians closer than San Isidro. For the rest of his life, the dog had an indentation on top of his head where the pus pocket had been. His name was Rambo. He certainly earned it.
Cloromiro Picado was a highly respected Costa Rican scientist who, among other distinctions, pioneered the development of the antivenin that is used in the treatment of snakebites. The institute that bears his name is known internationally for its leadership in this field. Highly trained handlers “milk” the snakes by holding them tightly and forcing their fangs through a thin rubber sheet stretched over a glass beaker. The venom flows into the beaker. Later it is injected into horses that, through repeated injections of ever-increasing strength, have developed a natural immunity to snake venom. Antibody-laden blood serum from the horses is the primary ingredient in the antivenin. On a visit to the institute I marveled at the large vipers, many in excess of two meters (6 ½ feet), and at the skill of the handlers. But the most fascinating drama of the day was a fight between two snakes.
Handlers released a terciopelo close to a very dark, gray snake with a metallic sheen. The challenger was called a mussurana (Clelia clelia,) and it soon became apparent that the terciopelo was outmatched. The terciopelo tried to hold its ground, striking and biting its opponent on several occasions. The mussurana waited for an opening and struck at the terciopelo’s head catching the upper mandible between its powerful jaws. The mussurana then wrapped around the viper, restraining its thrashing body while biting down hard on its snout, thus obstructing the passage of air through its nostrils. Within minutes, the terciopelo lay still. The mussurana began the long process of swallowing its prey. “This may take a couple of hours, said one of the handlers.” The institute has an ongoing study of the mussurana in hopes of learning about its resistance to the pit viper venom and how to apply it to the treatment of snakebite in humans.
Our family had grown fond of the two-and-a-half meter (8 foot) long serpent that, on many evenings, meandered across our back porch. We even gave it a name, “Zopy,” after its Spanish common name, “zopilota.” The chicken house, the yard and the surrounding area were all part of its territory. Its sheer size was enough to startle the most adventurous of our visitors, but the mussurana never caused any harm even to the chickens. I’m sure the terciopelos would beg to differ. During the eight years that Zopy hung out near our home, not a single terciopelo was seen closer than 300 meters (330 yards.)
Jack Ewing was born and educated in Colorado. In 1970 he and his wife Diane moved to the jungles of Costa Rica where they raised two children, Natalie and Chris. A newfound fascination with the rainforest was responsible for his transformation from cattle rancher into environmentalist and naturalist. His many years of living in the rainforest have rendered a multitude of personal experiences, many of which are recounted in his published collections of essays, Monkeys are Made of Chocolate & Where Jaguars & Tapirs Once Roamed. His latest book is, Monkeys are Made of Mangos.