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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
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.
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.
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.
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
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.
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.
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.
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.
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.
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
Getting the patient to medical help is the major priority.
General principles to consider:
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
Information courtesy www.ultimatefieldguide.com
Photographs of snake bites and technical assistance courtesy A. Naudé, Chairman: Transvaal Herpetological Association www.sareptiles.co.za
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