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

7. 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.

8. 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

9. 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

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

11. Neurotoxin vs vasculotoxin

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. General algorithm:

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

22. 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

23. 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

24. 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

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

26. • 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

27. • 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

28. 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

29. 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.