Dealing with snakebite on Safari

You are walking with your PH in the bush, stalking a buffalo. You take care to make no sound. As you step carefully over a tuft of grass you hear a load hiss and feel a blow on your lower leg, followed instantly by a sharp pain. You have been bitten by a puff adder.

The incidence of snakebites in Southern Africa is around 30-80 per 100,000 population per year in areas where snakes abound.

Only a very small percentage of these bites are fatal. Reliable snakebite statistics are currently not available on the deaths per year due to snakebites. However, it is estimated that it must be in the vicinity of 50 deaths per year.

If the mortality figure of snakebites is compared to those of motor vehicle accidents (10 000 per year) it is clear that snakes pose an insignificant health risk in Southern Africa. But snake bites still occur - especially in the bush.

Snake venom is designed to immobilize or kill prey, commence digestion and protect the snake against harmful ingested organisms.

Venom can be injected by biting or spat at the eyes of a perceived threat.

Types of Venom

Cytotoxic venom

Death from an puff adder bite is highly improbable. Cytotoxic venom attacks the skin and tissue and causes necrosis. The initial symptom is a painful swelling commencing at the bite site that is warm, often tender and spreads mainly up the limb or tissue. This may lead to swollen lymph glands within 2 hours after the bite.

Local complications include blistering, necrosis (dead tissue), localized bleeding, and infection.

The swelling may be so severe that it can cause compartment syndrome. This is a syndrome where the venom causes severe swelling of the underlying muscles. The muscles are surrounded by an nonelastic sheath and when the muscle swells it compresses the arteries and nerves that runs through the muscles within the sheath. The oxygen rich blood that flows through the arteries cannot reach the tissue under the occluded arteries and the tissue will then die due to the oxygen shortage.

If this condition is not corrected as a matter of urgency within a period of 4 hours. Usually surgery is needed to release the pressure by splitting the inelastic sheath. It may lead to tissue loss or even amputation in severe cases.

Compartment syndrome must be seriously suspected when the pain in the tissue below the swelling increases in severity and develops a “pins and needles“ feeling or numbness. An absent pulse below the swelling is usually a late sign and requires urgent surgical intervention.

Another frequent regional complication from cytotoxic venom is the development of a deep vein thrombosis (blood clot) in the affected limb. Systemic effects of the venom include low blood pressure, fluid on the lungs, difficulty breathing and a low platelet count which can lead to bleeding.

Systemic venom action producing edema and heart conduction defects has only been documented in Gabon adder bites, which are uncommon in South Africa as this snake is only found around St. Lucia.

The groups of snakes that has cytotoxic venom include the Gabon adder, Puff adder,  Mozambique spitting cobra, Stiletto snake, Night adder and other smaller adders.

Neurotoxic venom

The neurotoxic venom interferes with the impulse transfer from nerve endings to skeletal muscles leading to paralysis. The signs and symptoms can escalate rapidly from a feeling of numbness around the mouth, to sweating, drooping eyelids, drop in blood pressure, inability to keep the head upright, difficulty in walking, difficulty in swallowing (saliva running from the mouth) to where the patient stops breathing - and eventually without medical intervention, will lead to death.

Within a few minutes from a mamba bite there is numbness around the mouth that progress to relentless widespread muscle weakness leading to respiratory failure in 60-70% of cases.

Non-spitting cobras (Cape, Snouted and Forest) leads to early swelling around the bite site, a window period where the patient is apparently normal followed by fairly rapid onset of inadequate respiration due to paralysis (about 50% of cases).

 The group of snakes with neurotoxic venom include  Black and Green Mambas and the non Spitting Cobras: Cape, Snouted, Forest.

Haemotoxic venom

The venom interferes with the clotting cascade and by lowering the platelets in the blood. The Boomslang and Vine snakes are the two snakes most commonly responsible for bites to snake handlers. Their venoms are exclusively haemotoxic and acts on the clotting cascade preventing blood clotting which can cause internal and external bleeding.

Boomslang-induced clotting dysfunction is of slow onset, with potential death only occurring after several days. This allows time to get the Boom slang specific antivenom from the manufactures (phone: 011-882-9940).

There is currently no antivenom available for the Vine snake.

Although Gaboon and Puff adders have cytotoxic venom, it can also cause bleeding by reducing the platelets.

Combination venom

A syndrome of a mixed picture of cytotoxic and neurotoxic signs and symptoms are found in some snakebites. Among these symptoms are cranial nerves dysfunction (Cranial nerves mainly supplies the organs of the face, throat and neck, heart and intestines), which uncommonly leads to other skeletal muscle weakness and respiratory failure.

Venom from a Berg adderbite can cause loss of taste and smell.

The group of snakes with combination venom effects includes: Rinkhals, Berg adder, Garter snake, Shield- nosed snake

Allergic reaction

Exposure to venom either by skin contact or envenomation through a snakebite can cause an acute allergic reaction to patients that were previously exposed to the venom. The reaction can be compared similarly to an allergic reaction from a bee sting, ranging from a mild reaction to death within minutes after the bite. These type of reactions are usually limited to snake handlers or persons that was previously bitten by a snake.

In patients that deteriorate rapidly after a bite an allergic reaction must be seriously considered. There is a huge difference in treatment between envenomation by a snakebite and an allergic reaction against the venom. Symptomatic snake bites are usually treated by antivenom where as an allergic reaction is treated with adrenaline. The use of an Epipen (adrenaline injector) or other antihistamines is recommended.

Management

An analysis of 4 rural snakebite series involving 911 patients by Dr Roger Blaylock, one of the foremost authorities in South Africa on the management of snakebites, showed the following.

• 16% had no envenomation

• 77% developed progressive painful swelling

• 6% progressive weakness

• <1% bleeding

Prevention

The greatest cause of snake bite is people trying to kill the snake. When a snake is fighting for its life and it bites, it delivers far more venom than in a chance encounter.

Common sense is the gold standard in preventing snakebites:

Wear boots that covers the ankle and loose hanging long pants. Most of the snakebites are on the feet, ankle and lower leg.

• Don’t step over an obstacle if you cannot see what is on the other side.

• Don’t put your hand into a hole when you can’t see what is inside.

• Don’t handle snakes if you are not a professional snake handler.

• Don’t confront a dangerous snake

• Do not try to kill it

If you encounter a snake back of as fast as possible keeping your eye on the snake. However if you are so close that you are within striking distance and the snake is already engaged to strike stand dead still until the snake withdraws. Snakes only strike at movement

Prevent nocturnal bites by using a light, wearing footwear and sleeping in a snake proof dwelling (zip up tents).

Be careful of handling “ dead “ snakes as some elapids, notably the Rinkhals, may feign death.

Medical management

The majority of patients can not correctly identify the snake even with the help of pictures.

Because of this Dr Blaylock divided the snakebite victims into the following 3 groups according to the clinical picture at presentation.

• Painful Progressive Swelling

• Progressive Weakness

• Bleeding

The treatment of these patients with antivenom simplifies the treatment of snakebites drastically.

Antivenom is given in each of these groups according to set criteria based on signs and symptoms.

Patients also receive supportive treatment according to the organ systems affected e.g. ventilation support for patients with respiratory failure and platelets and blood clotting components for patients with active bleeding

First Aid

Getting the patient to medical help is the major priority.

General principles to consider:

• Remain calm and think before you act

• Remember: very few people die from snake bite

• Keep the patient calm and reassured.

• Immobilize the patient as far as possible and don’t waste time in delaying his transport to the nearest medical facility.

• Do not give the patient anything to drink or eat - especially not alcohol.

• Incision, suction, cryotherapy (freezing of bite site), electrotherapy, topical or ingested medication is of no value.

• Do not waste time by searching for and trying to kill the snake

• Pressure immobilization bandaging is not recommended as it may aggravate or precipitate tissue necrosis (death/destruction) or compartment syndrome as the majority of snakebites presents with progressive swelling.

• An arterial tourniquet is of value in known non-spitting cobra and mamba bites and should be reserved for cases with positive identification of one of the above group of snakes. Tourniquet application can cause severe underlying tissue damage if applied wrongly .It is best to leave it to people with the necessary training on tourniquet application. The tourniquet must be released every 30 min and not be kept on for longer than 2 hours.

• Patients who cannot swallow their saliva must be placed in the recovery position and closely observed for respiratory failure. The saliva can accumulate in the patient’s throat and prevents air entry in the lungs. If left unattended the patient can “drown” in his own saliva . Try to remove as much as possible of the saliva in the victim’s airways by either sucking or finger sweep. With finger sweep, wrap a gauze swab or a piece of absorbable clothing around your index and middle finger, and sweep your finger through the patients mouth and throat to remove as much as possible of the saliva manually

• When the patient becomes unresponsive or start having difficulties breathing, immediately start with CPR.

• UNless in an emergency, do not inject antivenom, the doctor should do that. Antivenom is very effective and should not be withheld to a patient with signs and symptoms that necessitate the administration of antivenom. However, the antivenom can cause a potentially severe allergic reaction.
  The incidence of potentially severe acute allergic reactions depends on the clinical indication for its administration ranging from 8% when given to patients with progressive weakness to 20% for patients with painful progressive swelling. Patients with bleeding from Boom slang bites can have an allergic reaction to the antivenom in up to 70% of cases.

• Antivenom  must preferably be given under medical supervision with adrenaline at the bedside.

• All snakebite victims should be hospitalized for at least 24 hours.

• Symptoms and signs of severe local or systemic poisoning occur sooner in children than in adults due to a higher venom concentration.

• The indications for antivenom administrations occur sooner and more frequently in children than in adults.

• The same amount of antivenom is given to children and adults.

• The venom from baby snakes is just as lethal as that of the adult snakes.

• The severity of the signs and symptoms and rate of deterioration of a victim, depends on the amount of venom injected during the bite and bite site.

• The closer the bites site to the heart the faster the signs and symptoms will appear.

• If the venom is injected directly into a vessel, rapid deterioration in the victim’s condition may be expected.

• One antivenom works for almost all the species that will kill you so you don’t have to wonder which antivenom you need. Boomslang have their own antivenom but all Mambas, Cobras, Rinkhals, Puff adders and Gaboon adders use the same antivenom called SAVP polyvalent antivenom.

Venom in the eyes

The Rinkhals and Mozambique spitting cobra are responsible for nearly all the cases of eye envenomation in Southern Africa. The Black spitting cobra and the Western barred spiting cobra can also be responsible for spitting in their victims eyes, although reported cases are uncommon.

The Rinkhals and Mozambique spitting cobra can spit accurately over a distance of up to 2 meters.

The Rinkhals needs to hood its neck to be able to spit whereas the Mozambique spitting cobra can spit from any position.

The eye is very vascular and venom in the eye can be rapidly absorbed. This can cause severe inflammation and painful spasm of the eyelid. If left untreated it may progress to inflammation of the cornea and ulcer formation, which may cause blindness. If correctly treated the effects are usually benign with full recovery expected within a week.

If hunting in Namibia there is a good likelihood that you will be spat at by a Western barred spitting Cobra. Remember that they are far more prolific venom producers than other spitters in Southern Africa.

General first aid principles for venom in the eyes

• if you get spat in the eye you cannot die from it, as the amount of venom absorbed can not make you sick or kill you

• Wipe the venom from the face

• Wash the eyes with copious amounts of fluid for at least ten minutes

• If water is not available any type of fluid can be used which is not harmful to the eyes like cold drinks, milk, beer etc. Urine can be used but only as the very last resort due to the ph levels and the risk of infection. Urine is not better to use than any other fluid

• Place an eyepad over the eyes if available and transport the victim to the nearest medical facility

• It is advisable to let an ophthalmologist examine the eyes

• Antivenom, either on the eyes or injected should not be used

Information courtesy www.ultimatefieldguide.com

Photographs of snake bites and technical assistance courtesy A. Naudé, Chairman: Transvaal Herpetological Association www.sareptiles.co.za