The Venoms of Snakes and Their Local Reactions

The Venom
Snakes in general are known for one very important feature they possess asides crawling uniquely on the floor as their means of movements. That particular feature is their venom. What is the venom all about? How and why is it poisonous and deadly to their victims? These, we will all consider.

Venom is modified saliva and 0.25 to 1 ml of it is injected into the victim when the snake bites. Enzymes such as phosphatidases, proteases, cholinesterases, hyaluronidases, ribonucleases, deoxyribonucleases, ophioxidase, lecithinase and erepsins are present in the venom. In addition, the venoms of Cobra and krait also contain non-ensymatic components like basic polypeptides which are highly neurotoxic. These toxins produce neuromuscular block.

The viperine venoms contain hemorrhagic, necrotic, coagulant and hemolytic substances leading to extensive damage to several tissues. Lesions are due to intravascular coagulation, fibrinolysis, damage to the vascular endothelium and extensive necrosis. The venoms of sea snakes are neurotoxic and they also cause extensive necrosis of the muscles.

The speed of action of the venom depends upon the site of injection and the amount of venom injected. If the venom directly enters the blood stream, the effect may be rapid and lead to sudden death. In most of the cases, the absorption of venom is slower and especially in viperine bites with extensive local reaction, considerable amount of venom may remain locally to be absorbed into circulation in due course.

The severity of en-venomation depends upon the circumstances of the bite. Bites sustained during the early part of the night are generally more serious since the poison sacs of the snake are full at this time. Bites through clothes are less dangerous. Children and underweight persons suffer more than normal adults since the concentration of the venom is relatively higher in them. Violent physical activity helps in disseminating the venom rapidly and thereby worsens the prognosis.

Clinical features: Severe fright and mental agitation leading to tachycardia, sweating, hypotension and even vascular collapse are prominent features soon after the bite. These nonspecific symptoms may be seen in all snake bites.

Local reactions: Local reactions are more prominent in the case of viper bites and less so in others. Intense pain, swelling and violaceous discoloration develop within minutes and often serosanguinous (bloody) fluid exudes from the fang marks. The edema and discoloration spread proximally and in a few hours vesicles and hemorrhagic blebs may appear. Rarely, gangrene may supervene.