Snakes Toxicology

Medical toxicological aspects of snakes with emphasis on classification of snakes and their venom, identification of snakes, fatal dose, fatal period, signs and symptoms of snake bite, diagnosis of snake bite, management, post-mortem findings and medico-legal aspects especially of the common Indian snakes.

1. Snakes Adhavan. M Ⅱ MBBS IGMC&RI Puducherry

2. Nomenclature: Phylum - Chordata Class - Reptilia Order - Squamosa Sub-order - Serpentes

3. Classification Poisonous snakes King cobra (Ophiophagus hannah) Common cobra (Naja naja) Russell’s viper (Daboia rusellii) Saw scaled viper (Echis carinatae) Pit viper Krait Non-poisonous snakes Sand boa Vine snake Rat snake Mud snake

4. Poisonous vs non-poisonous snakes

5. Poison apparatus: Modified salivary (parotid) glands Consists of- Gland - lies below & behind eyes above upper jaw Duct - carries venom from gland to fang Fangs - 2 curved teeth on maxillary bones along jaws. Grooved in cobras, kraits; tubular in vipers; solid in non-poisonous snakes.

6. Snake venom: Saliva of snake ejected from poison apparatus Actions - neurotoxic or vasculotoxic or myotoxic Physical appearance - faint transparent yellow, viscous Toxic principles - Toxic principles Clinical effect Phospholipase A2, lecithinase Mycotoxic, neurotoxic, cardiotoxic Serine protease, other proteases Hemolysis Hyaluronidase Local tissue destruction Acetylcholine esterase Neurotoxic, relaxes muscles α-bungarotoxin, cobratoxin Post synaptic inhibition β-bungarotoxin, crotoxin Pre synaptic inhibition

7. Fatal dose: Snake Fatal dose (dried form)(mg) Cobra 15 King cobra 12 Common krait 2.5-6 Banded krait 10 Russell’s viper 40 Saw-scaled viper 8

8. Fatal period: Immediate - due to shock from fright Cobra - ½-24 hours Krait - 12-24 hours Viper - 1-4 days

9. Neurotoxin vs vasculotoxin

10. Signs & symptoms of Ophitoxemia/envenomation (poisonous snake bite): Most common symptom is fear Semi-consciousness, cold clammy skin, hypotension, rapid breathing, shock Local signs - fang marks, pain, bleeding, inflammation, local infection, abscess formation, necrosis Dry bite - snake fails to inject venom

11. Cobra bite Local symptoms in 6-8mins Reddish wheal develops; tenderness, burning pain; wheal becomes putrid in 1-2 days; purplish, sloughing appears Early symptoms - vomiting, heaviness of eyelids, blurred vision, paresthesia around mouth, hyperacausis, headache, dizziness, vertigo, hyper salivation, congested conjunctiva, gooseflesh Muscle weakness, paralysis: lower limbs first, ascends to respiratory muscles - death

12. Krait Similar to cobra, but less rapid Abdominal pain, ptosis, dysarthria, dysphagia, chest pain, quadriparesis, respiratory paralysis, death No nausea, froth Drowsiness is more Bite is painless and nocturnal - victims usually die in sleep

13. Viper More local reaction with pain & oozing Extensive local necrosis leading to gangrene Appearance of serous & serousanginous blisters b/l parotid swelling, conjunctival edema, sub-conjunctival haemorrhage Petechial haemorrhage, epistaxis, gum bleeding, hemoptysis, hemetamesis, hematuria, fundal haemorrhage, bleeding from bite site & rectum Acute renal failure - evident by oliguria, anuria, rising serum creatinine Death is due to circulatory failure, hemorrhagic complications

14. Sea snake Painless bite, no local swelling, local lymph node involvement Early symptoms - headache, thirst, sweating, vomiting Generalised rhabdomyolysis - muscles become tender and painful on movement; paralysis, ptosis develops Myoglobinuria within 3 hours of bite

15. Snake venom ophthalmia: When spat venom enters eyes, there is Immediate & intense burning Stinging pain Watering of eyes Whitish discharge Congested conjunctiva Spasm, swelling of eyelids Photophobia Clouding of vision

16. Diagnosis of snake bite: History - time of bite, description of snake Examination - including neurologic examination Urinary detection of venom Radioimmuno assay - most sensitive, specific Enzyme immuno assay ELISA 20 minute whole blood clotting test - bedside test; 20WBCT + clot lysis test - Viperidae species Single breath counting test - Elapidae species

17. Management: Observe the patient for 8-12 hours if skin is broken & snake cannot be established as non-poisonous Avoid incision over bite, mouth suctioning, tourniquet around limb, snake stones, ice packs, electric shock Management includes: Prevention of spread of venom Anti-venom treatment Supportive treatment

18. General algorithm:

19. Prevention of spread of venom: Reassurance Immobilisation - slows systemic absorption Pressure immobilisation - for elapids; delays absorption Avoid manipulation - avoids infections, increased absorption, local bleeding

20. Antivenom treatment: Lyophilised (freeze dried) polyvalent antisnake venom (ASV) - effective against common poisonous snakes Dose: lyophilised ASV(10ml/vial) is dissolved in water; 80-100ml is to be dissolved in 200-500ml of isotonic saline; given as slow I.V. Mild cases: 5 vials; moderate cases: 5-10 vials; severe cases: 10-20 vials Should not be given at local bite site Same dose for children and adults Patient to be observed for at least 1 hour after starting infusion

21. Supportive treatment: Ventilatory care for bulbar paralysis, respiratory failure Care of bitten area - antibiotics, TT Surgical excision - prevent gangrene, extension of infection Anticholinesterase - prevents increased secretions, sweating, bradycardia Hypotension, shock management - I.V. fluids, plasma expanders, dopamine

22. Supportive treatment contd. Oliguria, renal failure - diuretics given if urine output <400ml/24 hours; hemodialysis in vasculotoxic bite Hemostatic disturbance - fresh blood, FFP, cryoprecipitate, platelet concentrates in viperine bites; heparin to manage DIC Corticosteroid therapy - anaphylaxis Snake venom ophthalmia - wash eye, mucous membranes immediately with large volumes of water

23. Postmortem findings: Poisonous snakes leave 2 fang marks along with smaller teeth marks Non-poisonous snakes leave semi-circular set of teeth marks

24. In Viperine bite there is Discolouration, swelling, cellulitis about the mark Haemorrhage from puncture site, mucous membranes Petechiae in mucosa of urinary bladder, stomach, intestines Regional lymph nodes - swollen, hemorrhagic Haemorrhages into bowel, lungs, endocardium Kidneys- inflamed, show medullary haemorrhages, tubular necrosis, cortical necrosis, interstitial nephritis Internal organs congested

25. In elapidae bite Site of bite contains fluid, hemolyzed blood causing staining of vessels No definite appearances indicating cause of death Only asphyxia is evident Bite marks are 1-1.5 cm deep in colubrine & 2.5 cms deep in viperine bites

26. Medico-legal aspects: Poisoning is usually accidental Occasionally homicidal by throwing snake over bed of sleeping person Very rarely suicidal Cattle are sometimes poisoned as revenge Bodies of poisoned animals may be eaten safely but their blood is poisonous if injected into human body If doctor fails to identify the snake when killed snake is bought with the patient, it amounts to negligence

27. References: Biswas G. Organic irritants-Animal. In: Review of forensic medicine and toxicology. Third edition. New Delhi: Jaypee brothers medical publishers(P)Ltd; 2015. p 524-533. Modi P. Jaising. Irritant poisons-animal poisons-snakes (ophidia). In: A textbook of medical jurisprudence and toxicology. Sixth edition. Bombay: Butterworth & Co. (India) Ltd; 1940. p 661-664.