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Snake Bite is a medical emergency that needs rapid first aid and treatment to prevent the venom from circulating to the heart and other organs of the body. There are over 2700 species of snakes worldwide and only about 500 of these species are venomous (Rattlesnake, Cobra, Tree Snakes, etc); this means that only about 500 species of snakes worldwide have venom (poison) that is lethal to the body.
All venomous snakes have fangs at the front of their mouth whereby they inject venom from their parotid gland into a victim when bitten by a snake.
Classification of Venomous snakes
- Viperidae: consist of vipers and adders. This is subdivided into two subfamilies: Viperinae which are true vipers (such as Russel Viper) and Crotalinae which include the pit vipers such as rattlesnakes that have long erectile fangs. They have triangular heads and short fat bodies.
- Elapidae: this family of land snakes has short fixed fangs covered by a gum fold, and their venom produces neurotoxic effects. They are very poisonous. The venom from some species of the Elapidae family such as the African spitting cobra produces local tissue necrosis (local skin becomes dead and slough off). Members include the mambas and cobras
- Hydrophidae: the members of this family of species of snakes have short fangs and flattened tails. Their venom produces myotoxic effect (they destroy and paralyze the muscles).
- Colubridae: the fangs of these snakes are grooved and posteriorly situated. Their venom is hematotoxic (that is, the venom destroys the blood)
Epidemiology of snakebite
Snakes are found all over the world except in the permanently Arctic and Antarctic regions of the world. In the tropics, snake bites are only seen among subsistence farmers while snake bites from pets such as dogs or cats remain the major source of snake bites in the western world. At least 50% of people bitten by snakes suffer few or no toxic effects since little or no venom has been injected.
Snake Venom Constituents
Snake venoms are complex mixtures of enzymes, low molecular weight polypeptides, glycoproteins, metal ions, and many other substances. The snake venom produces multiple systemic effects on their victims following a bite. The Russel viper venom for example contains at least two proteases that activate mammalian blood clotting cascade causing disseminated intravascular coagulopathy (DIC)
RVV-X is a glycoprotein that activates factor X by calcium-dependent reaction and also acts on factor IX and protein C.
RVV-V is an arginine ester hydrolase that activates factor V. Phospholipase A2 damages mitochondria, red blood cells, leucocytes (white blood cells), platelets, and vascular endothelium. The Hyaluronidase serves to promote the spread of venom through tissues.
Neurotoxins such as bunarotxins and cabrotoxins prevent the release of acetylcholine at the neuromuscular junction. Biogenic amines such as histamines and 5-hydroxytryptophan (serotonin) are found particularly in viper venom contribute to local pain and permeability changes at the site of a snake bite.
Symptoms and Signs
- Local pain at the site of snake bite
- Bleeding from the site of snake bite
- Pain starts to extend from the site of snakebite to other parts of the limbs (leg or hand depending on where the bite was or other parts of the body)
- Swelling of the affected part and also of the affected limb
- Pain in regional lymph nodes
- Early syncope (fainting)
- Angioneurotic edema
- Wheezing may occur after biting by some vipers
- Bleeding from old sites of wound or scars and also from the gums (gingival bleeding) especially when the bite is from Vipers or Colubridae family
- Paralysis is common with Elapidae and Hydrophidae causing blurring of vision (affecting muscles of the eyes), ptosis, hyperacusis, hypersalivation (over salivation), and goose flesh.
- Myoglobinemia (brownish plasma) and myoglobinuria (reddish-brown urine) are common with snake bites by sea snakes.
What to do when bitten by a snake
- Allay anxiety of victim
- In cases of venomous spit to eyes, a large volume of water should be used to flush the eyes
- Immobilize the limb affected
- Do not tamper with the wound
- Avoid harmful and time-wasting treatment
- Take the patient to the nearest hospital with the snake if it has been killed
Wrong first aid measures to AVOID
- Avoid incision on the wound
- Avoid suction or sucking out the venom with your mouth
- The use of tourniquets is controversial. Dangers include increased swelling, increased bleeding, and increased local effects of toxins. However, in snake bite caused by Elapidae family of snakes, tourniquet.
- Rapid assessment of symptoms and signs of snake bite. If the snake is killed and available, ascertain whether it is a venomous snake or not.
- If the patient is in shock (evidenced by sudden collapse, sweating, cold clammy hands and legs, low blood pressure, and fast heartbeat (tachycardia)), then the foot of the bed should be raised and intravenous infusion of plasma expanders should be started immediately.
- Blood should be taken for grouping and cross-matching
- Early anaphylactic symptoms should be treated with adrenaline and anti-histamine
- Blood should be taken immediately for packed cell volume (PCV), clotting profile, urea and electrolytes, and creatine kinase.
- Urinalysis for myoglobinuria and hemoglobinuria
- The patient should be questioned about symptoms of envenomation as mentioned above such as heaviness of eyelids and drowsiness.
- Use of Antivenom
- Other supportive management may include blood transfusion
Anti Snake Venom
In the management of snakebite, the most important decision is whether or not to give antivenom because it may produce severe reactions and also, it is very costly.
Indications for Anti Snake Venom
- Presence of systemic envenomation especially hypotension (low blood pressure), electrocardiographic abnormalities, vomiting, hemostatic abnormalities, polymorphonuclear leucocytosis, elevated serum creatine kinase.
- Local envenoming: after snake bite on hand or foot, swelling extends beyond the wrist or ankle within 4 hours of the snake bite
Adrenaline must be at hand for the treatment of anaphylactic reactions to the antivenom itself.
The overall mortality rate is about 2%. It is highest in the Elapidae family of snakebite which can be as high as 25% mortality; it is about 2 to 5% in Viperidae family. More children die from snake bites than adults. Snakebites in the trunk, face, and neck carry a higher rate of death than when the bites were on the limbs (legs and hands). Death due to respiratory failure may occur within 6 hours of snakebite following a bite from Elapidae species.
- Visual abnormalities
- Acute renal failure
- Cardiac arrest following hyperkalemia is caused by acute renal failure as well as tissue and muscle breakdown.
- Respiratory failure
- Clear bushes around the house
- Keep rodents away from home by use of rodenticides
- Avoid keeping chickens around the house
- Always use booths while working on the farm or while entering the bush
- Always use a bright light source while walking in the night
- Do not put your hand or leg under objects kept for long such as stones or dumped objects around the house