SNAKE BITES & SCORPION STINGS / MedUrgent

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SNAKE BITES & SCORPION STINGS




Snakes and scorpions secrete venom by means of special glands when they bite or sting humans. The venom is secreted into the torn skin when the snake takes a bite or else it may be injected through a wound that is caused by the scorpion's thorn. The scorpion's venom is placed in a reservoir in its tail from where it is injected. Snakes preserve their venom in the parotid gland and are passed to humans through the frontal fangs. The clinical effect of the poison depends on the amount of venom injected, age of the patient, site of the bite and effectiveness of the treatment, however, with a scorpion sting, the effect is not in proportion to the amount of venom injected.


SNAKE BITES


Though most of snake venoms are lethal, mortality and morbidity are low. There are 3 families of snakes which are poisonous. All have fangs at the front of their mouths by which the venom is injected from the parotid glands.




These are:

a) Elapidae which are mainly neurotoxic. They are land snakes that have relatively short fixed front fangs e.g. cobra, coral snakes, tiger snakes, mambas and kraits. They usually cause local tissue necrosis.

b) Viperidae which are vasculotoxic. These are land snakes with long erectile fangs. They are divided into two forms

1- Pit (crotaline) vipers, which have a thermosensitive pit between the eyes and nostrils. e.g. rattle snake. 
2- Viperine vipers that do not have the pit and are the true vipers. They are found in all parts of the world except America and the Asian Pacific area. 
c) Hydrophiidae which are myotoxic. These are sea snakes. They have short fangs and flattened tails. The venom released has the following characteristics: It is a low molecular weight polypeptide that contains multiple toxins that cause muscle damage and possibly myoglobinaemia. It also contains phospholipids and glycolipids.




CLINICAL PICTURE

This is governed by certain factors:

• The species of snake, and therefore the venom constituent.

• Fright or fear of a painful death, which is blown out of proportion to the degree of toxicity.

• General effects i.e. local pain and possibly the fang marks.

• Venom effect which may be local or systemic. The local effects are due to the vasculotoxins which may cause epithelial damage and is cytolytic (cause tissue damage). This is manifested in viperine viper bites. There is also oedema and blisters. The systemic effect is seen in all types, but mainly the neurotoxins. There is a generalized effect which is spread by the blood vessels. The autonomic or the somatic nervous system may be affected and similarly the striated muscles. This leads to excessive salivation, sweating, hypotension, nausea, vomiting and paralysis of muscles of the eye leading to squint, muscles of deglutition, muscles of respiration and muscles of the heart. There is very little local reaction in the neurotoxic form. Bleeding caused by the viparine form leads to epistaxis, hematuria, GIT bleedings and bleeding from the bite site. Certain types of venoms lead to shock, arrhythmia, rhabdomyolysis with myoglobuliuria (black urine), descending paralysis with ophthalmoplegia, bulbar and respiratory muscle paralysis. 

TREATMENT

- Reassurance and close observation for at least 24 hours.

- Immobilization of the affected limb, but no tourniquet or aspiration of the wound and no ice or herbal medicines should be used. Clean the wound and debride the dead tissue

- IV fluids should be given and also sedation.

- Anti-tetanic serum

- Anti- venom when there is systemic effect only as they may lead to severe allergic reactions. The anti-venom should be diluted in normal saline (1:3) to be given as slow infusion (15 drops /min) .

- Intubation and ventilation if there is respiratory paralysis and dialysis should be done for renal failure.


 SCORPION STINGS






 

 




Scorpion venom is more toxic than most snake venoms, but the injected amount is usually minute. In scorpions, paired poison glands are found in the distal region of the tail. The poison may cause immediate intense local pain, erythema, swelling and ecchymosis. 

Systemic manifestations include acetylcholine and catecholamine release e.g. fever, sweating, excessive salivation, vomiting, nystagmus, blurring of vision, agitation, hypertension, convulsions and coma. Respiratory failure, renal failure, DIC and pancreatitis may also occur. 



TREATMENT

• Apply a firm pressure bandage to prevent spread of the neurotoxin. Local anaesthetic may be used followed by general supportive measures and analgesic.

• Diazepam is used. (no phenobarbitone or opiates as they potentiate the toxin)

• Anti-venom for children

• Atropine for life-threatening bradycardia and to reduce the secretions

• Diazoxide or prazosin (0.5mg P.O. every 3-6hrs) for hypertension

• Diazepam or medazolam for agitations 

• Dobutamine for left ventricular Failure (do not use digoxine or Beta blockers)

• Apply proper management of DIC.

Symptoms should disappear within 2 to 4 hours of giving the antivenom.

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