Treating and Preventing Venomous Snake Bites

by US Department of Health and Human Services

They fascinate. They repel.

Some pose a danger. Most are harmless.

And whether they are seen as slimy creatures or colorful curiosities, snakes play important environmental roles in the fragile ecosystems of the nation's wildlife areas.

People who frequent these wilderness spots, as well as those who camp, hike, picnic, or live in snake-inhabited areas, should be aware of potential dangers posed by venomous snakes. A bite from one of these, in which the snake may inject varying degrees of toxic venom, should always be considered a medical emergency, says the American Red Cross.

Every state but Maine, Alaska and Hawaii is home to at least one of 20 domestic poisonous snake species, according to a study in the August 1, 2002, issue of The New England Journal of Medicine. The article's authors estimate that between 7,000 and 8,000 people a year receive venomous bites in the United States, and about five of those people die. Some experts say that because people who are bitten can't always positively identify a snake, they should seek prompt care for any bite, though they may think the snake is nonpoisonous. Even a bite from a so-called "harmless" snake can cause an infection or allergic reaction in some individuals.

Medical professionals sometimes disagree about the best way to treat poisonous snakebites. Some physicians hold off on immediate treatment, opting for observation of the patient to gauge a bite's seriousness. Procedures such as fasciotomy, a surgical treatment of tissue around the bite, have some supporters. But most often, doctors turn to the antidote to snake venom — antivenin — as a reliable treatment for serious snakebites.

There are two types of antivenin (sometimes called "antivenom") in use today. They are derived from antibodies created in the blood of a horse or sheep when the animal is injected with snake venom. In humans, antivenin is injected either through the veins or into muscle, and it works by neutralizing snake venom that has entered the body. The first antivenin, derived from horse blood, was introduced in the United States in 1954. Because this antivenin is obtained from horses, snakebite victims who are sensitive to horse proteins must be carefully managed. The danger is that they could develop an adverse reaction or even a potentially fatal allergic condition called anaphylactic shock.

Newer kinds of antivenins derived from sheep have been studied, and one (CroFab) is now licensed for use in the United States. This sheep antibody preparation has been digested with an enzyme to reduce the risk of allergic reactions. The enzyme treatment also allows the antivenin to be cleared from the body more rapidly, so that additional treatments may need to be given.

The Food and Drug Administration regulates antivenins as part of its oversight of biological products. The agency requires certain criteria to be met before these materials are sold, including standards for purification, packaging and potency. The FDA also regulates antivenin labeling, ensuring that data on potential side effects and other pertinent information are available. The agency also periodically inspects antivenin production facilities to ensure compliance with regulations.

Types of Poisonous Snakes

Two families of venomous snakes are native to the United States. The vast majority are pit vipers, of the family Crotalidae, which include rattlesnakes, copperheads and cottonmouths (water moccasins). Pit vipers get their common name from a small "pit" between the eye and nostril that detects heat and allows the snake to sense prey at night. These snakes deliver venom through two fangs that the snake can retract at rest, but which spring into biting position rapidly. Virtually all of the venomous bites in this country are from pit vipers. Some — Mojave rattlesnakes or canebrake rattlesnakes, for example — carry a neurotoxic venom that can affect the brain or spinal cord. Copperheads, on the other hand, have a milder and less dangerous venom that sometimes may not require antivenin treatment.

The amount of venom actually delivered by a pit viper bite varies. "Some 20 to 30 percent of patients we see who have been bitten by a snake, who actually have fang marks, have not received any venom at all," says Edward L. Hall, M.D., a Thomasville, Ga., trauma surgeon who treats snakebites." He says one reason for this may be poor timing by the snake. "Pit vipers have a very sophisticated mechanism that allows them to deliver venom at the exact instant the teeth are sunk into the flesh. So it has to be precise timing. But what we often see is that the [snake's timing is off and] venom is squirted on the pants leg or released prematurely."

The other family of domestic poisonous snakes is Elapidae, which includes two species of coral snakes found chiefly in the Southern states. Related to the much more dangerous Asian cobras and kraits, coral snakes have small mouths and short teeth, which give them a less efficient venom delivery than pit vipers. People bitten by coral snakes lack the characteristic fang marks of pit vipers, sometimes making the bite hard to detect.

Though coral snakebites are rare in the United States — only about 25 a year by some estimates — the snake's neurotoxic venom can be dangerous. A 1987 study in the Journal of the American Medical Association examined 39 victims of coral snakebites. There were no deaths, but several victims experienced respiratory paralysis, one of the hazards of neurotoxic venom.

Some nonpoisonous snakes, such as the scarlet king snake, mimic the bright red, yellow and black coloration of the coral snake. This potential for confusion underscores the importance of seeking care for any snakebite (unless positive identification of a nonpoisonous snake can be made).

The bites of both pit vipers and coral snakes can be effectively treated with antivenin. But other factors, such as time elapsed since being bitten and care taken before arriving at the hospital, also are critical.

First Aid for Snakebites

Over the years, snakebite victims have been exposed to all kinds of slicing, freezing and squeezing as stopgap measures before receiving medical care. Some of these approaches, like cutting into a bite and attempting to suck out the venom, have largely fallen out of favor.

"In the past five or 10 years, there's been a backing off in first aid from really invasive things like making incisions," says Arizona physician David Hardy, M.D., who studies snakebite epidemiology. "This is because we now know these things can do harm and we don't know if they really change the outcome."

Many health-care professionals embrace just a few basic first-aid techniques. According to the American Red Cross, these steps should be taken:

• Wash the bite with soap and water.
• Immobilize the bitten area and keep it lower than the heart.
• Get medical help.

About the Author

The Department of Health & Human Services is the United States government's principal agency for protecting the health of all Americans and providing essential human services, especially for those who are least able to help themselves. The department includes more than 300 programs, covering a wide spectrum of activities.