Quick Answer
Snake bite kills roughly 58,000 Indians every year — the highest national burden globally — and is a WHO Neglected Tropical Disease. NEET PG examiners test envenomation almost every year across medicine, forensic and community-medicine papers.
- Big Four — Russell's viper (hemotoxic), Common krait (neurotoxic, painless nocturnal bite), Indian cobra (neurotoxic + local necrosis), Saw-scaled viper (hemotoxic).
- First-aid — reassure, immobilise the limb, remove tight items, transport fast; NEVER apply tourniquet, cut, suck, ice, or traditional-healer remedies.
- 20-minute WBCT — bedside coagulopathy screen; unclotted at 20 minutes = mandatory ASV.
- Polyvalent ASV — 10 vials IV over 1 hour for any systemic envenomation; repeat every 6 hours until WBCT normalises; no maximum dose.
- Neostigmine plus atropine — works for post-synaptic cobra neurotoxicity; does NOT work for pre-synaptic krait.
- Ptosis is the earliest sign of neurotoxic envenomation — bilateral within 1-2 hours.
- Red scorpion sting — prazosin 30 microgram/kg orally every 3-6 hours is the cornerstone; cuts mortality from 30 percent to under 5 percent.
- Complications — AKI (often prolonged), Sheehan-like hypopituitarism (Russell's), compartment syndrome, ARDS, chronic kidney disease.
Snake bite is the most heavily under-reported public-health emergency in India — the Million Death Study estimates around 58,000 deaths annually, more than any other country, driven overwhelmingly by rural agricultural workers with delayed presentation and dependence on traditional healers. The WHO added snake bite to the Neglected Tropical Disease list in 2017, and the Indian Ministry of Health has since folded ASV into PMJAY coverage and pushed community stocks to the primary-health-centre level.
This NEETPGAI deep dive covers the Big Four venomous species, syndrome recognition (hemotoxic vs neurotoxic vs myotoxic), the 20-minute WBCT bedside test, polyvalent ASV dosing and anaphylaxis management, neostigmine indications, and the special case of Indian red scorpion sting where prazosin is the life-saver. Pair this with the tropical fever differential guide for the broader tropical-medicine cluster.
Snake bite epidemiology in India
- Annual deaths — approximately 58,000 (Million Death Study, Lancet 2020)
- State burden — Uttar Pradesh, Andhra Pradesh, Bihar, Madhya Pradesh, Rajasthan, Odisha — the "high-burden 8" states account for over 70 percent of deaths
- Peak season — June to September (monsoon); increased human-snake contact
- Population at risk — farmers, agricultural labourers, children walking to fields, families sleeping on the floor (krait bites)
- Legal status — notifiable disease in most states; WHO NTD since 2017; national target to halve deaths by 2030
The Big Four — species, venom and syndrome
| Snake | Distribution | Venom class | Signature syndrome |
|---|
| Russell's viper (Daboia russelii) | All India, prefers scrubland and crop fields | Hemotoxic + mild neurotoxic | Local swelling, DIC, AKI, capillary leak, pulmonary oedema, late panhypopituitarism |
| Common krait (Bungarus caeruleus) | All India except NE and high Himalayas | Neurotoxic (pre-synaptic) | Painless nocturnal bite, ptosis, respiratory paralysis; minimal local signs |
| Indian cobra (Naja naja) | All India | Neurotoxic (post-synaptic) + cytotoxic + cardiotoxic | Ptosis, local necrosis, occasional cardiac arrest |
| Saw-scaled viper (Echis carinatus) | Rajasthan, Gujarat, MP, Karnataka dry belts | Hemotoxic | DIC, AKI, spontaneous bleeding |
Regional add-ons the polyvalent ASV does NOT reliably cover
- King cobra (Ophiophagus hannah) — Western Ghats and Northeast; large venom volume, neurotoxic
- Hump-nosed pit viper (Hypnale hypnale) — Western Ghats and Kerala; produces AKI and coagulopathy that is under-recognised and does not respond well to polyvalent ASV
- Malabar pit viper, banded krait, monocled cobra — regional species with variable ASV response
- Sea snakes — myotoxic; myoglobinuria and hyperkalaemia
Envenomation syndromes — how to recognise at the bedside
Neurotoxic syndrome (cobra, krait)
The single earliest sign is bilateral ptosis appearing within 1-2 hours of a systemic envenomation. Progression follows a descending pattern:
- Ptosis (levator paralysis)
- External ophthalmoplegia, blurred vision, diplopia
- Broken-neck sign — inability to lift the head off the pillow
- Dysphagia, pooling of saliva
- Dysarthria, weak cough
- Respiratory muscle paralysis (diaphragm) → respiratory failure
- Limb weakness, areflexia
- Coma from hypoxia (venom does not cross the blood-brain barrier)
Krait vs cobra clinical clues — krait bites are usually painless and occur at night in sleepers with minimal or no local swelling; cobra bites are painful with prominent local swelling and often local necrosis.
Hemotoxic syndrome (viper)
- Local — swelling starting within minutes, ecchymosis, hemorrhagic blebs, blistering, progressive limb oedema
- Coagulopathy — venom-induced consumption coagulopathy (VICC); prolonged 20-WBCT; low fibrinogen, high D-dimer
- Spontaneous bleeding — gum bleed, epistaxis, haematuria, PV bleed, intracranial haemorrhage
- AKI — within 24-48 hours from a combination of DIC-related microangiopathy, direct nephrotoxicity, rhabdomyolysis and pre-renal from hypotension; often needs 2-4 weeks of dialysis
- Capillary leak syndrome (Russell's) — pulmonary oedema, ascites, hypoalbuminaemia
- Panhypopituitarism (late Russell's) — anterior pituitary apoplexy from vascular occlusion; presents weeks later with amenorrhoea, hypothyroidism, hypocortisolism (Sheehan-like)
Myotoxic syndrome (sea snakes, some kraits)
- Myalgia, muscle tenderness
- Myoglobinuria — dark tea-coloured urine
- Hyperkalaemia from rhabdomyolysis → cardiac arrhythmia
- AKI
First-aid and pre-hospital care
The single most important first-aid message is rapid transport and do no harm.
Do:
- Reassure the patient (fear-induced sympathetic surge can mimic shock)
- Immobilise the bitten limb with a splint (like a fracture)
- Remove rings, watches, tight clothing before swelling develops
- Transport by the fastest available vehicle to a hospital with ASV
- Keep the patient warm and hydrated (oral if not vomiting)
- Note the time of bite and any progression of symptoms
Do NOT:
- Apply a tight tourniquet (causes ischaemia, compartment syndrome, and a bolus of venom on release)
- Cut and suck the wound (increases infection and blood loss)
- Apply ice, heat, kerosene, cow-dung or traditional-healer poultices
- Use electric shock ("stun-gun therapy" — no evidence, dangerous)
- Give aspirin or NSAIDs (worsen bleeding)
- Wait for symptoms to develop before transport
The WHO now permits pressure-immobilisation bandaging for elapid (cobra, krait) bites in Australia and the Pacific — this is NOT part of standard Indian first-aid because most Indian community responders cannot apply it correctly and it can worsen viper envenomation.
Hospital management — the ASV protocol
Step 1 — Rapid assessment and resuscitation
- ABC — airway (intubate for descending paralysis or coma), breathing (ventilate if respiratory failure), circulation (IV fluid for hypovolaemic shock)
- IV access — two large-bore cannulae
- Baseline investigations — 20-WBCT (see below), CBC, urea, creatinine, LFT, INR, aPTT, fibrinogen, D-dimer, urinalysis, ECG, chest X-ray, blood group and crossmatch, ABG
- Cardiac monitor — arrhythmia risk in cobra bite and hyperkalaemia
- Foley catheter — urine output monitoring for AKI
Step 2 — The 20-minute Whole Blood Clotting Test
The 20-WBCT is the pillar of Indian snake-bite management:
- Draw 2 mL of fresh venous blood into a clean, dry glass test tube (not plastic — plastic cannot activate the contact pathway)
- Leave undisturbed at room temperature
- Tilt at 20 minutes
- Firm clot — normal coagulation, no viper envenomation currently
- No clot or fragile clot — venom-induced consumption coagulopathy → mandatory ASV
Repeat every 6 hours after ASV until it normalises; then daily for 24-48 hours to catch late recurrent coagulopathy from tissue-bound venom release.
Step 3 — Indications for ASV
Systemic envenomation, defined as any of:
- Positive 20-WBCT (unclotted at 20 minutes)
- Spontaneous systemic bleeding
- Neurotoxic signs (ptosis, ophthalmoplegia, dysphagia, respiratory weakness)
- Cardiotoxicity (arrhythmia, ST changes)
- Myoglobinuria or muscle tenderness with rhabdomyolysis
- Haemodynamic instability
- AKI (rising creatinine)
- Progressive local swelling extending beyond 2 joints, or beyond half the limb within 8 hours (soft indication)
Local swelling alone without any systemic sign is NOT an indication for ASV.
Step 4 — ASV dosing
- Indian polyvalent ASV — covers Russell's viper, common krait, Indian cobra, saw-scaled viper (lyophilised equine F(ab prime)2 or IgG)
- Starting dose — 10 vials reconstituted and infused in 100-200 mL of normal saline over 1 hour
- Paediatric dose is the SAME as adult — venom load is fixed, not body-weight dependent
- Repeat 10 vials every 6 hours if:
- 20-WBCT still abnormal
- Neurotoxic signs progressing
- New systemic bleeding
- No maximum dose — continue until clinical response
- Monitor bedside for anaphylaxis every 10-15 minutes during infusion
Step 5 — Managing ASV anaphylaxis
Reactions occur in 5-10 percent of ASV doses. Pre-medication with subcutaneous adrenaline 0.25 mL of 1:1000 is done in some centres, but evidence is conflicting.
If a reaction develops:
- Stop the ASV infusion
- IM adrenaline 0.5 mL of 1:1000 in the anterolateral thigh (repeat every 5 minutes if needed)
- IV hydrocortisone 100-200 mg
- IV chlorphenamine 10 mg
- Nebulised salbutamol for bronchospasm
- IV fluid bolus for hypotension
- Oxygen high-flow
- Restart ASV once stable — envenomation is more lethal than the reaction
Step 6 — Neostigmine for post-synaptic neurotoxicity
Neostigmine works for cobra bite but not for krait bite — a favourite examiner distinction.
- Cobra alpha-neurotoxin — binds reversibly to nicotinic ACh receptor; neostigmine (AChE inhibitor) raises synaptic ACh and displaces the toxin
- Krait beta-bungarotoxin — pre-synaptic phospholipase; destroys the presynaptic terminal irreversibly; requires days-to-weeks of ventilator support until axonal regeneration
Neostigmine trial:
- Atropine 0.6 mg IV (block muscarinic side effects)
- Neostigmine 50-100 microgram/kg IV or IM
- Assess ptosis, dysphagia and respiratory effort at 30 minutes
- Improvement confirms post-synaptic toxicity — repeat every 30 minutes
Step 7 — Supportive management by system
- Coagulopathy after ASV — FFP 15-20 mL/kg if bleeding persists despite normalising 20-WBCT (ASV neutralises circulating venom but does not restore already-consumed clotting factors)
- Blood transfusion — PRBC for symptomatic anaemia (Hb less than 7 g/dL, or less than 8 with cardiac disease)
- AKI — early haemodialysis for uraemia, hyperkalaemia, acidosis, fluid overload; recovery over 2-4 weeks is typical; up to 10-20 percent progress to CKD
- Compartment syndrome — measure pressure; fasciotomy only if pressure greater than 30-40 mmHg with clinical signs, and preferably after coagulopathy has been corrected
- Wound care — debridement of necrotic tissue after coagulopathy corrects; tetanus toxoid; antibiotics only if infected (not routine prophylaxis)
- Respiratory failure — intubation and mechanical ventilation for descending paralysis; wean as neurotoxin clears
Complications — acute, subacute and chronic
Acute (hours to days)
- Respiratory failure (neurotoxic)
- Hypovolaemic and distributive shock
- Acute kidney injury
- DIC and severe haemorrhage
- Compartment syndrome
- Myocardial infarction, stroke
- Anaphylaxis to ASV
Subacute (days to weeks)
- Prolonged dialysis-dependent AKI
- Wound necrosis requiring debridement or amputation
- Deep vein thrombosis
- Secondary infection
- Serum sickness (5-14 days post-ASV) — fever, rash, arthralgia; treat with steroids
Chronic
- Chronic kidney disease following severe AKI — up to 20 percent of dialysis-dependent AKI survivors
- Sheehan-like hypopituitarism (Russell's viper) — presents weeks-to-months later
- Amputation and contractures
- Post-traumatic stress and neuropsychiatric sequelae
- Loss of livelihood — agricultural workers unable to return to fieldwork
Scorpion sting — the Indian red scorpion
The Indian red scorpion (Mesobuthus tamulus) is the world's most lethal scorpion species. Endemic to Maharashtra (Konkan belt), coastal Karnataka, Chhattisgarh, and parts of Andhra Pradesh and Kerala. Children are most affected; case-fatality was over 30 percent in the pre-prazosin era.
Pathophysiology
Venom activates voltage-gated sodium channels and prolongs the action potential in autonomic nerve terminals. This produces a biphasic catecholamine storm:
- Parasympathetic surge (early) — vomiting, salivation, sweating, priapism, bradycardia, hypotension
- Sympathetic storm (dominant) — hypertension, tachycardia, myocardial injury, cool peripheries, pulmonary oedema, cardiogenic mixed shock
Clinical features
- Local pain at sting site (not severe swelling — distinguishes from snake bite)
- Restlessness, sweating, priapism (children), vomiting
- Hypertension progressing to hypotension
- Tachycardia, gallop, third heart sound
- Pulmonary oedema, tachypnoea, hypoxaemia
- Cool clammy peripheries, mottled skin
- ECG — ST changes, T inversion, arrhythmias, occasionally MI
Management — the prazosin protocol
The intervention that transformed Konkan-belt mortality from over 30 percent to under 5 percent:
- Prazosin 30 microgram/kg orally every 3-6 hours until warm peripheries, pulmonary oedema resolves, and tachycardia settles
- Prazosin is a selective alpha-1 antagonist that offloads sympathetic-driven vasoconstriction and pulmonary oedema WITHOUT the beta-blocker risks
- Scorpion antivenom (SAV) — controversial; recent Indian RCTs (KEM Mumbai, Sevagram) suggest benefit when given early with prazosin; used variably
- Supportive — oxygen, IV fluid cautiously, dobutamine for cardiogenic pulmonary oedema (adds inotropy without further increasing afterload), mechanical ventilation for severe cases
- Avoid — pure beta-blockers (unopposed alpha vasoconstriction) and digitalis (arrhythmogenic in acute myocarditis)
India-specific programmes and policy
- WHO NTD since 2017 — snake bite recognised as a Neglected Tropical Disease
- PMJAY coverage — ASV is included in the Ayushman Bharat package
- Community ASV stocking — Ministry directive to stock ASV at every 24x7 PHC in high-burden districts
- Snakebite Envenomation Health Action Plan (SEHAP) — national plan launched 2023 targeting a 50 percent reduction in deaths by 2030
- Training — MOs at PHC level trained in 20-WBCT and initial ASV under NHM
- Notifiable disease — most states require reporting; enforcement variable
- Community awareness — bed nets to prevent krait bites (sleeping on floor), torches at night, closed footwear in fields, sealed housing gaps
- Research — species-specific monovalent ASV (against hump-nosed pit viper) is under development at ICMR-NIE and CIIMS
- Anti-scorpion venom (SAV) — produced by Haffkine Institute Mumbai; supply and cost limitations restrict widespread use
NEET PG MCQ traps
- Big Four — Russell's, krait, cobra, saw-scaled viper.
- Painless nocturnal bite — think krait.
- Earliest neurotoxic sign — bilateral ptosis (1-2 hours).
- 20-WBCT — clean glass tube, 2 mL blood, 20 minutes; unclotted = coagulopathy.
- ASV starting dose — 10 vials IV over 1 hour; same dose in paediatric patients.
- ASV anaphylaxis rate — 5-10 percent.
- Anaphylaxis treatment — IM adrenaline 0.5 mL of 1:1000 anterolateral thigh; then restart ASV.
- Neostigmine works for cobra (post-synaptic); does NOT work for krait (pre-synaptic).
- Neostigmine dose — 50-100 microgram/kg IV/IM after atropine 0.6 mg.
- Russell's viper late complication — panhypopituitarism (Sheehan-like).
- AKI in snake bite — often prolonged 2-4 weeks; 10-20 percent progress to CKD.
- First aid — reassure, immobilise, transport; NEVER tourniquet, cut, suck, ice.
- Compartment syndrome — fasciotomy only after coagulopathy corrected.
- FFP — only if bleeding persists after ASV corrects the 20-WBCT.
- Sea snake bite — myotoxicity, myoglobinuria, hyperkalaemia.
- Hump-nosed pit viper — Western Ghats; polyvalent ASV NOT effective.
- Red scorpion — Mesobuthus tamulus; Konkan belt; children worst affected.
- Prazosin dose — 30 microgram/kg PO every 3-6 hours.
- Prazosin mechanism — selective alpha-1 antagonist.
- Avoid beta-blockers in scorpion sting (unopposed alpha vasoconstriction).
- Dobutamine for scorpion cardiogenic pulmonary oedema.
- Serum sickness — 5-14 days post-ASV; steroids.
- WHO NTD status — snake bite added in 2017.
- Indian burden — approximately 58,000 deaths per year.
- ASV manufacturers in India — VINS Bioproducts, Bharat Serums, Haffkine, Premium Serums.
Key takeaways
- The Big Four cover most Indian bites; regional species (hump-nosed pit viper, king cobra) do not respond well to polyvalent ASV.
- The 20-minute WBCT is the pillar of bedside decision-making — cheap, fast and decisive.
- ASV is dose-fixed (10 vials) regardless of age or weight; repeat every 6 hours until response.
- Neostigmine works for cobra, not krait — this distinction recurs on every paper.
- Russell's viper leaves a long tail — CKD, panhypopituitarism, contractures.
- Red scorpion sting is a paediatric emergency in the Konkan belt — prazosin is the game-changer.
- First-aid mistakes (tourniquets, cutting, traditional healers) still kill people who would otherwise reach ASV alive.
Frequently asked questions
Which are the Big Four venomous snakes of India and what venom syndromes do they produce?
The Big Four responsible for the majority of India's roughly 58,000 annual snake-bite deaths are Russell's viper (Daboia russelii), Common krait (Bungarus caeruleus), Indian cobra (Naja naja) and Saw-scaled viper (Echis carinatus). Russell's viper causes the classic Indian hemotoxic syndrome — local swelling, ecchymosis, disseminated intravascular coagulation, acute kidney injury, capillary leak with shock and pulmonary oedema, and late panhypopituitarism (Sheehan-like from anterior pituitary infarction). Common krait produces a painless, often nocturnal bite in sleeping victims and a purely neurotoxic syndrome — bilateral ptosis, external ophthalmoplegia, dysphagia and progressive respiratory paralysis with minimal or no local signs. Indian cobra bite gives mixed neurotoxicity plus local necrosis and, less commonly, cardiotoxicity. Saw-scaled viper produces a hemotoxic picture similar to Russell's but usually without pituitary involvement. The Indian polyvalent ASV covers all four; the hump-nosed pit viper (Western Ghats) and king cobra are important regional add-ons the polyvalent ASV does NOT reliably cover.
How is the 20-minute Whole Blood Clotting Test performed and what does it indicate in snake bite?
The 20-minute Whole Blood Clotting Test (20-WBCT) is the single most useful bedside test in Indian snake bite because it needs only a dry glass tube, is cheap and gives an answer at the bedside in 20 minutes. Draw 2 mL of fresh venous blood into a clean glass test tube (plastic will not work — the surface needs to activate contact factors), leave undisturbed at room temperature and tilt at 20 minutes. If a firm clot forms the coagulation cascade is intact; if the blood remains liquid or a fragile clot forms, the patient has venom-induced consumption coagulopathy — which in Indian settings usually means Russell's viper or saw-scaled viper envenomation and is a mandatory indication for polyvalent ASV. The 20-WBCT is repeated every 6 hours until it normalises after ASV to confirm venom neutralisation, then daily for 24-48 hours to catch recurrent coagulopathy from tissue-bound venom re-release.
What is the standard dose of polyvalent anti-snake venom in India and how are anaphylactic reactions managed?
Indian polyvalent anti-snake venom (ASV) is a lyophilised equine F(ab prime)2 or IgG preparation raised against the Big Four. The standard adult and paediatric starting dose in a patient with systemic envenomation is 10 vials of ASV reconstituted and infused in 100-200 mL of normal saline over 1 hour. The dose is repeated if the 20-WBCT remains abnormal or neurotoxic signs persist after 6 hours; there is no maximum dose because ASV neutralises circulating venom on a molar basis. Anaphylactic reactions occur in 5-10 percent of doses — features range from urticaria and pruritus to bronchospasm, hypotension and full anaphylaxis. Some centres pre-medicate with subcutaneous adrenaline 0.25 mL of 1:1000 to reduce reaction rates (evidence conflicting). If a reaction occurs, stop the ASV infusion, give IM adrenaline 0.5 mL of 1:1000 in the anterolateral thigh, IV hydrocortisone, IV chlorphenamine, fluid resuscitation and oxygen — then restart the ASV once stable because envenomation is more lethal than the reaction.
When is neostigmine effective in a neurotoxic snake bite and when will it not work?
Neostigmine works in post-synaptic neurotoxin envenomations — the classic example is the Indian cobra, whose alpha-neurotoxin binds reversibly to the nicotinic acetylcholine receptor at the neuromuscular junction. Neostigmine (an acetylcholinesterase inhibitor) raises synaptic acetylcholine and competitively displaces the toxin, restoring neuromuscular transmission. The dose is 50-100 microgram/kg IV or IM, preceded or accompanied by atropine 0.6 mg IV to block the muscarinic side effects (bradycardia, hypersalivation, bronchorrhoea). A positive response — improvement in ptosis or dysphagia within 30 minutes — is diagnostic of post-synaptic toxicity and can be repeated every 30 minutes. Neostigmine does NOT work in common krait envenomation because krait beta-bungarotoxin is a pre-synaptic phospholipase that irreversibly damages the presynaptic terminal — the only treatment for krait paralysis is timely ASV, meticulous airway protection and mechanical ventilation until axonal sprouting restores transmission (may take days to weeks).
How is Indian red scorpion sting managed and what is the role of prazosin?
The Indian red scorpion (Mesobuthus tamulus) is the world's most lethal scorpion species and endemic to Maharashtra, Karnataka coastal belts, Chhattisgarh, and parts of Andhra Pradesh and Kerala. The venom produces a catecholamine storm through sodium-channel activation — initial parasympathetic surge (vomiting, salivation, sweating, priapism) is rapidly overtaken by a sympathetic storm with severe hypertension, tachycardia, myocardial injury, pulmonary oedema and eventual cool-peripheries mixed shock. Prazosin is the pharmacological cornerstone — 30 microgram/kg orally every 3-6 hours until warm peripheries, tachycardia settles and priapism resolves. It is a selective alpha-1 antagonist that offloads the sympathetic-driven vasoconstriction and pulmonary oedema without the beta-blockade risks. Scorpion antivenom (SAV) has debated efficacy — recent Indian RCTs (from KEM Mumbai and Sevagram) suggest a benefit when given early alongside prazosin, but prazosin alone remains the intervention that has cut Konkan-belt mortality from over 30 percent to under 5 percent. Supportive care includes oxygen, dobutamine for cardiogenic pulmonary oedema, and mechanical ventilation for severe cases.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team
Reviewed by: Pending SME Review
Last reviewed: July 2026
