A farmer was sleeping in the field, and he felt a sting on his leg. He saw something moving away quickly. He then got drowsy and was taken to the hospital. He developed pain around the site and continued to bleed profusely from the wound site. The wound became red with blisters. Which of the following is the most likely cause?

Correct Answer: A. Viper

Viper envenomation is the most likely diagnosis based on the clinical presentation. The key discriminating features are: (1) profuse bleeding from the wound site — vipers are hemotoxic snakes that cause coagulopathy and hemorrhage; (2) local tissue damage with redness and blisters at the bite site — characteristic of viper venom's proteolytic enzymes; (3) drowsiness/lethargy — early systemic manifestation of viper bite. In India, the "Big Four" venomous snakes are cobra, krait, viper, and saw-scaled viper. Vipers (Echis carinatus, Vipera russellii) cause predominantly hemotoxic envenomation with coagulopathy (PT/INR prolongation, thrombocytopenia), leading to uncontrolled bleeding. Local effects include severe pain, edema, blistering, and tissue necrosis. The farmer's presentation of continued profuse bleeding with local inflammation and blistering is pathognomonic for viper bite. Cobra bites, by contrast, cause neurotoxic effects (paralysis, respiratory failure) with minimal local tissue damage. The clinical picture here is clearly hemotoxic, not neurotoxic.

Why the other options are wrong

B. Cobra — Cobra venom is neurotoxic, causing flaccid paralysis, ptosis, and respiratory failure — not profuse bleeding or local blistering. While cobra bites may cause minimal local swelling, they do not produce the hemorrhagic diathesis or extensive local tissue necrosis seen in this case. The absence of neurological signs (paralysis) rules out cobra. C. Lad Scorpion — Scorpion stings cause local pain and erythema but not profuse bleeding or coagulopathy. Systemic effects are primarily neurotoxic (tremors, salivation, priapism in some species) or cardiotoxic, not hemorrhagic. The degree of bleeding and blistering described is inconsistent with scorpion envenomation. D. Wasp bite — Wasp stings are non-venomous insect injuries causing local pain, erythema, and urticaria only. They do not cause profuse bleeding, coagulopathy, or systemic drowsiness. The severity of bleeding and systemic symptoms described far exceeds what a wasp sting could produce.

High-Yield Facts

Mnemonics

VIPER = Hemorrhage; COBRA = Paralysis Viper → Vasculotoxic (hemotoxic) → bleeding, coagulopathy. Cobra → Central nervous system → paralysis, respiratory failure. Use when differentiating snake bite presentations. Bleeding + Blisters = Viper If you see profuse bleeding + local blistering + coagulopathy, think viper (hemotoxic). If you see paralysis + minimal local damage, think cobra (neurotoxic).

NBE Trap

NBE pairs "drowsiness" with neurotoxic cobra bite to lure students into choosing cobra; however, drowsiness in viper bite is due to shock from hemorrhage and coagulopathy, not neurological paralysis. The profuse bleeding is the discriminating feature that rules out cobra.

Clinical Pearl

In rural India, viper bites account for ~60% of snake bite deaths, primarily due to delayed presentation and coagulopathy-induced hemorrhage. A farmer with profuse bleeding and local tissue damage should receive anti-viper serum (AVS) and fresh frozen plasma (FFP) immediately to correct coagulopathy — delay increases mortality from uncontrolled bleeding.

_Reference: Robbins Ch. 9 (Environmental & Nutritional Pathology); Park's Textbook of Preventive & Social Medicine (Snake Bite Management); Forensic Medicine & Toxicology (Reddy) — Snake Bite Classification_