SNAKE BITES

 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 live in snake-inhabited areas, should be aware of potential dangers posed by venomous snakes. A bite from one of these, in whichthe snake may inject varying degrees of toxic venom, should always be considered a medical emergency, says the American Red Cross.

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.

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 through the veins, 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 FDA regulates antivenin.

Types of Poisonous Snakes

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. 

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, 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, several victims experienced respiratory paralysis, one of the hazards of neurotoxic venom.

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, 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.

The main thing is to get to a hospital and don't delay, most bites don't occur in real isolated situations, so it is feasible to get prompt medical care. The longer it takes to get treatment started the odds of long-term complications increase. Some medical professionals, along with the American Red Cross, cautiously recommend two other measures:

·   If a victim is unable to reach medical care within 30 minutes, a bandage, wrapped two to four inches above the bite, may help slow venom. The bandage should not cut off blood flow from a vein or artery. A good rule of thumb is to make the band loose enough that a finger can slip under it.

·   A suction device may be placed over the bite to help draw venom out of the wound without making cuts. Suction instruments often are included in commercial snakebite kits.

Treatment Drawbacks

Antivenins have been in use for decades, sometimes there are reactions to them, even life-threatening reactions, but then you're treating a life-threatening situation. It's clearly a case of weighing the risks versus the benefits.

Another complicating factor is the diverse potency of venom. Venom can vary within species and even within litter mates--brothers and sisters.

The only way to look at snakebites is on an individual basis and on the patient's actual reaction to the venom. Basic signs like pain, swelling and bleeding, along with more complicated reactions such as ecchymosis (purple discoloration), necrosis (tissue dies and turns black), low blood pressure, and tingling of lips and tongue give medical professionals clues to the seriousness of bites and what treatment route they should take.

Some experts emphasize that, although antivenin can effectively reverse the effects of venom and save life and limb, there is no guarantee that it can reverse damage already done, such as tissue necrosis. Some patients may later require skin grafts or other treatment. The potential for limiting complications is one compelling reason to seek medical treatment as soon as possible after a snakebite.

Avoiding Snakebites

Some bites, such as those inflicted when snakes are accidentally stepped on or encountered in wilderness settings, are nearly impossible to prevent. But experts say a few precautions can lower the risk of being bitten:

·   Leave snakes alone. Many people are bitten because they try to kill a snake or get a closer look at it.

·   Stay out of tall grass unless you wear thick leather boots, and remain on hiking paths as much as possible.

·   Keep hands and feet out of areas you can't see. Don't pick up rocks or firewood unless you are out of a snake's striking distance. (A snake can strike half its length.)

·   Be cautious and alert when climbing rocks.

Just walk around the snake, giving it a little berth--six feet is plenty. But leave it alone and don't try to catch it.

How NOT to Treat a Snakebite

·   No ice or any other type of cooling on the bite. Research has shown this to be potentially harmful.

·   No tourniquets. This cuts blood flow completely and may result in loss of the affected limb.

·   No electric shock. This method is under study and has yet to be proven effective. It could harm the victim.

·   No incisions in the wound. Such measures have not been proven useful and may cause further injury.

Venom properties
Snake venoms may contain 20 or more components. More than 90 per cent of the dry weight is protein, in the form of enzymes, non-enzymatic polypeptide toxins, and non-toxic proteins.

 Clinical features
Fear and effects of treatment as well as the venom contribute to the symptoms and signs in those bitten by snakes. Even patients who are not envenomed may feel flushed, dizzy, and breathless and may notice constriction of the chest, palpitations, sweating. Tight tourniquets may produce congested and ischemic limbs; local incisions at the site of the bite may cause bleeding and sensory loss and herbal medicines often induce vomiting. The earliest symptoms directly attributable to the bite are local pain and bleeding from the fang punctures, followed by pain, tenderness, swelling and bruising extending up the limb, lymphangitis, and tender enlargement of regional lymph nodes. Early syncope, vomiting, colic, diarrhea, angio-edema, and wheezing may follow bites by some snakes. Nausea and vomiting are common symptoms of severe envenoming.

General indications for antivenom
Antivenom is indicated if there are signs of systemic envenoming such as:

1.Haemostatic abnormalities such as spontaneous systemic bleeding, incoagulable blood, or thrombocytopenia
2.Neurotoxicity
3.Hypotension and shock, abnormal ECG, or other evidence of cardiovascular dysfunction
4.Impaired consciousness of any cause
5.Generalized rhabdomyolysis.

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