Snake Envenomation

Snakes are one of the venomous organisms found on earth that lead to a large number of accidental bites. An estimated figure of 50,000 cases of snake bite related deaths are said to occur in India but the number is likely to be much more. The low availability of snake antivenom in India is the major reason for death as well as the difficulty in the identification of the type of snake along with delay from a primary care centre to a tertiary care centre.

Snakes are reptiles that are venomous as well as non-venomous. The venom is a mixture of enzymes, toxins and other proteins which a highly modified form of saliva (same is the case with spider venom). It is stored in venom sacs. Mostly injected and in some species also sprayed (as in the case of the spitting cobra which targets the eyes of its victim). Snake venoms may be cardiotoxic, neurotoxic or hemotoxic. Sometimes the snake may not inject its venom on biting a victim. Such a bite is referred to as a dry bite which is why careful evaluation must be done before administering an antivenin.

Snakes are broadly divided in the following families and thus their venom also have common characterises.

Viperidae: hemotoxic: vipers

Elapidea: Neurotoxic: cobras, kraits

Hydrophilidae: Mostly neurotoxic, often more toxic than land snakes. Coral snake

The venom classification is not concrete, for example, snakes belonging to elapidea are not always neurotoxic, some are cytotoxic. Also, when we refer to a snake as hemotoxic it is not just hemotoxic, there will be other toxic compounds in the venom too. Venoms of all organisms have hundreds of compounds some toxic and some not. This may not be the case with creatures that use toxins instead of venoms. Note the difference between venom and toxin. Venoms are injected toxins are not this is in the context of a living creature. But in the context of a substance, a toxic substance is something that is simply deadly or poisonous/noxious.

Thus, a poison dart frog is not venomous but toxic. But snakes, spiders and scorpions are venomous not toxic. And all their venoms contain toxic substances, which are protein in nature.

Poisons: master call of all noxious compounds, manmade or natural.

Toxins: poisonous substances generally of natural origin, generally secreted (as in case of frogs) but not necessary (as in the case of mushrooms) also generally the term is given to a specific compound (example: bungarotoxin, or cobra toxin)

Venom: toxic substances not one compound but a cocktail, a term collectively given to a mixture of substances biologically produced by an organism and specifically delivered via a route of injection as in the case of snakes, spiders, scorpions, bees, hornets and many more creatures.

Most snake bites are accidental occurring in fields, or at night when one accidentally walks over a snake, often bare feet. It may also occur when one accidentlly picks up a snake while picking up firewood or something similar. Or while in a hut when a snake may enter in search of prey and accidentlly stumble upon a victim. Death after envenoming takes place after several hours or days but not within minutes. The amount of venom available in the venom sac may be limited however it’s enough to kill hundreds of humans and may not be exhausted on repeated bites.

Symptoms and signs: These mainly depend on the type of snake. Generally, there will be extreme pain at the wound site. But in certain type of snakes such as kraits a sleeping person may not even wake up when bitten.

Cardiovascular symptoms will be common in case of Viperidae family of snake bites, such as arrhythmia, pulmonary oedema, shock, hypotension. Local necrosis. haemostatic abnormalities are common.

Bleeding and clotting disorders are also common with the Viperidae family of snakes due to the hemotoxic nature of venoms. Traumatic and spontaneous bleeding of the body can be seen, intracranially, in body cavities, from eyes, gums etc. wound site will constantly be oozing fluid, there may be dermatological reactions at the site. Since some venoms have proteolytic and cytotoxic enzymes and nature. Inflammation is severe and obvious.

Neurotoxic venoms will cause paralytic symptoms, ophthalmic abnormalities such as Ophthalmoplegia or droopy eyelids and flaccid muscles.

In many cases, there will be a breakdown of muscle tissue leading to myoglobinuria and kidney damage.

Swelling of hand on being bitten by a venomous snake


Drooping eyelids, the result of neurotoxic venom


Reaction at the bite site

Management:

It is always best to avoid traditional remedies since they do more harm than good. The ultimate solution is a snake antivenom.

Reassure the victim. Often the patient is agitated worried and thus there is worsening of symptoms. Immobilised the affected body part and arrange for transportation of victim directly to a tertiary hospital. Since not every snake bite is a venomous an appropriate identification of the situation is mandatory before anti-snake venom is administered. It is a concoction of specific or paraspecific immunoglobulins. In India it is often available in lyophilised form since cold storage is necessary for the liquid form which is the better version.

All patients may need supportive therapy with fluids and respiratory support.

Deciding the dose is a tough task as literature mentions the dose in the form of the number of vials required to be administered in terms of the degree of envenomation and it is extremely difficult to judge the degree of envenomation. However, WHO guidelines give a detailed and exact dose of ASV to be used based on the type of snake. These guidelines are available specifically for South Asian countries are a reliable source of literature for study and guide.

On administration of ASV with supportive treatment immediate improvement should be ideally seen, especially with regards to bleeding gums cardiotoxic and neurotoxic improvements may be seen after several hours.

Some patients may have an anaphylactic reaction to the antivenom and epinephrine must be at hand for the same.

After, treatment through a full recovery can be expected in some cases in many this is not the case. Some patient may develop extensive irreversible local and end organ damage. Some may have loss of some hormonal gland function, kidney failure. In still other cases patients end up developing carcinoma at the bite site many years later.

WHO GUIDELINES highly recommended: http://apps.searo.who.int/PDS_DOCS/B4508.pdf