Snakes: Difference between Poisonous and Non-Poisonous

Snake Bites- Everything about Snakes a Doctor should know

Snakes – An overview

Types of Poisonous snakes

1. Colubridae: e.g. African boomslanag snake, twig snakes.
2. Alractaspididae: e.g. mole vipers or adders.
3. Elapidae: e.g. cobra, krait, coral snake.
4. Viperidae: e.g. Russell’s viper, saw-scaled viper.
5. Hydrophidae: e.g. Sea snakes.

Fig: Fangs in different snake families

Difference between Poisonous and Non-Poisonous Snakes

Figure- A to H: Important features of poisonous and non-poisonous snakes: (A) Poison apparatus and fangs (canalised and grooved), (B) Ventral shields (belly scales) and vertebrals, (C) Head scales, (D) Cobra (note the hood and spectacle mark) (E) Cobra – Third supralabial touching eye and nasal shield, (F) Krait — four infralabials (note the large fourth one), (G) Krait — enlarged vertebrals on the back, and (H) Pit viper — a pit between eye and nostril.

Common Non-Poisonous Snakes in India

1. Rat snake (Dhaman)
2. Vine snake
3. Bronze back tree snake
4. Banded kukri
5. Sand boa

Features of Common Poisonous Snakes in India

1. Common cobra

Fig: Common cobra

Fig: Dorsal aspect of cobra with marks

• Common cobras are usually brown or black in color
• Head is covered with shields. The third supra-labial shield touches the eye and nose
• A small wedge shaped scale called as cuneate is present between 4th and 5th infra-labials
• Pupils are round
• Hood is present. Dorsal aspect of hood may have monocellate (monocele) or binocellate (spectacle) mark. Ventral surface of hood have two dark spots
• Fangs are short, grooved and situated anteriorly
• Tail is cylindrical. Caudal scales (scales on undersurface of tail) are divided and double
• Venom — neurotoxic.

2. Common Krait

Fig: Common krait

Fig: Common krait head

• Usually steel blue or black in color with single or paired white bands on back. The bands are more distinct towards the tail
• Pupils are round
• Large hexagonal scale presents over back
• The 4th infra-labial scale is the largest scale of other infra-labial scales
• The subcaudal (ventral scales distal to vent) are undivided and entire
• Fangs are short, grooved and situated anteriorly
• Venom — neurotoxic.

Banded Krait

Fig: Banded krait

• Inverted “V” shaped mark on head
• Broad black and yellow glistening bands encircle the body. On cross-section, the bands are triangular in shape
• As per habitat, the snake is shy in nature often seen basking near water bodies usually in morning hours
• Venom — neurotoxic.

Saw Scaled Viper

Fig: Saw scaled viper

• Aggressive snake
• Viviparous
• Usually brown in color and grows up to 1.5 to 2 feet
• Head triangular with small scale. White “arrow mark” or “spear mark” may present on head
• Pupils are vertical
• Wavy white line (zig-zag pattern) may present on each flank
• Diamond shaped markings over back
• Belly scales are broad and cover entire width
• The scales of viper are serrated, saw like thus name sawscale viper
• Fangs are long, curved, hollow, channelised and hinged
• Venom — vasculotoxic and hemotoxic.
•  (Can also be remembered as 5 V’s; V= viper, V=viviparous, V=vertical pupil, V=v shaped head (triangular), V=vasculotoxic venom).

Russell’s Viper

Fig: Russell’s viper

• Head is large, flat and triangular with small scales. White V shaped mark present on head
• Pupils are vertical
• Large nostrils
• Body is stout and fatty with brown or yellowish color.
• Body scales are semi-elliptical
• Three rows of chained dark spots present on back
• Tail is narrow and short. Scales are divided into two rows
• Fang are long, curved, hollow, channelised and hinged
• When disturbed, makes a loud and hissing sound
• Venom — Vasculotoxic and hemotoxic.

Sea Snakes

• Sea snakes are usually bluish, grayish or greenish in color. They have prominent nostrils and are situated on the top of snout
• Body is flat and belly scales are not broad
• Tail is flattened and paddle shaped
• Venom — myotoxic.

Venom

Neurotoxic Venom

• Origin—Common in Elapidae snakes, e.g. krait, cobra, etc.
• Action—Acts like Curare, mainly on the motor nerve cells and results in muscular paralysis, the muscles are affected in following order:
• >Firstly—Muscles of the mouth
• >Secondly—Muscles of the throat
• >Finally—Muscles of respiration
• Symptoms at bite site—Local manifestations are least with neurotoxic venom snake bite.
• Other symptoms—Convulsions may be seen with Cobra venom (Krait venom produces only paralysis).

Haemotoxic Venom

• Origin—Common in Viperidae snakes, e.g. Pit viper (Crotalidae); Pit-less viper (Russell’s viper, Saw scaled viper/Phoorsa/Echis/Echis Carinata), and Bamboo snake (Common green pit viper).
• Action—Acts by cytolysis of endothelium of blood vessels, lysis of red cells and other tissue cells and coagulation disorders. All these can lead to:
• >Severe swelling with oozing of blood and spreading cellulitis at bite site. Blood from such patients fails to clot even on adding thrombin, because of very low level of fibrin.
• >Necrosis of renal tubules, and
• >Functional disturbances like convulsions, due to intracerebral haemorrhage.

Myotoxic Venom

• Origin—Common in hydrophidae or sea snakes
• Action—Produces generalized muscular pain, followed by:
• >Myoglobinuria within 3 to 5 hours.
• >Death usually occurs due to respiratory failure.

So What is the Fatal Dosage for Venom?

Clinical Features

Non-Poisonous Snake

1. Fear and apprehension
2. Sweating
3. Patient may be in state of shock with feeble pulse, hypotension, syncope, rapid and shallow breathing
4. Bite area — may show multiple teeth marks

Poisonous snake

• Fang marks
• Burning pain
• Swelling and discoloration sometimes associated with some blisters
• Serosanguinous discharge from bite site
• In comparison with viper bite, local manifestations are milder in elapid bite.

Fig: Bite area in elapid bite

• Pre-paralytic stage — characterized by vomiting, headache, giddiness, weakness, lethargy
• Paralytic stage — characterized by spreading paralytic features with ptosis, ophthalmoplegia, drowsiness, dysartheria, convulsions, bulbar paralysis, respiratory failure and death.

Fig: Flow chart showing clinical features in elapid bite

• Rapid swelling of the bitted site
• Discoloration
• Blister formation — may extend to entire limb and even spread to trunk
• Bleeding from bite site
• Pain

Fig: Local features in Viperid bite

Fig: Local features in Viperid bite

• Generalized bleeding—epistaxis, hemoptysis, hemetemesis, bleeding gums, hematuria, malena, hemorrhagic areas over skin and mucosa
• Shock
• Renal failure

• Local swelling
• Pain

• Myalgia
• Muscle stiffness
• Myoglobinuria
• Renal failure

Diagnosis

1. Identification of fang marks
2. Identification of snake—vide supra
3. Laboratory methods

Fang marks

Laboratory methods

• Complete blood count—leucocytosis may be evident with thrombocytopenia
• Smear — hemolysed and fragmented RBCs
• Increased prothrombin time and increased partial thromboplastin time

• Immunodiagnosis — consist of:

1. Immunodiffusion
2. Counter-current immunoelectrophoresis
3. ELISA
4. Radioimmunoassay

Management

General Measures

• Allay the anxiety and fear
• Reassure the patients that all snakes are not poisonous
• Avoid alcohol or morphine, for these can increase the rate of absorption of venom.

First aid and field management

Fig: First aid in snakebite

• Reassurance
• Limit systemic spread of venom by immobilizing the affected part (e.g. limb)
• For Viperid bites, the bitten limb should be splinted if possible and kept at approximately heart level
• For elapid or sea snakebites, the Australian pressure immobilization technique is beneficial. In this method, the entire bitten limb is wrapped with an elastic or crepe bandage and then splinted
• Tourniquet—a proximal lymphatic-occlusion constriction band or torniquet may limit the spread of venom if applied within 30 minutes. The tourniquet should be applied such that it does not prevent arterial flow of blood and the distal pulsation should be appreciated.

Hospital Management

• Monitor vital signs, cardiac rhythm, oxygen saturation and urine output
• The level of local edema/swelling/erythema in the bitten limb should be marked and the circumference should be measured every 15 minutes until swelling has stabilized
• Intravenous access with fluid resuscitation. If needed, vasopressors (e.g. dopamine) should be administered
• Blood and urine should be collected for laboratory evaluation
• Care of bite site — apply dry sterile dressings. Splint may be applied
• Tetanus immunization should be updated as appropriate
• If the swelling in the affected limb continues and impending tissue perfusion causing muscle compartment syndrome, intracompartmental pressure should be checked. If pressure is elevated prompt surgical consultation should be obtained while antivenin continues
• Antivenin therapy—antivenin should be administered only when indicated. Table 38.5 displays indication for administration of antivenin. Antivenins are available as monovalent (i.e. species specific) or polyvalent. In India, polyvalent antivenin is available that is effective against common cobra, common krait, Russell’s viper and sawscaled viper. The antivenin should be administered with caution. Usually the antivenins are of equine origin and carry risk of anaphylaxis or delayed-hypersensitivity type of reactions. Prior to administration of antivenin infusion, the patient should receive appropriate loading doses of intravenous antihistamines. The antivenin should be administered as intravenous infusion. It should be dissolved in 500 ml of normal saline or Ringer’s lactate or 5% dextrose for adults and 20 ml/kg for children. The adverse reactions of antivenin are mentioned in Table 38.6
• Severe hemorrhage or bleeding may require blood or fresh frozen plasma
• If there are features of neurotoxicity, neostigmine may be required. Every injection of neostigmine should be preceded with atropine
• Oxygen, ventilatory support
• Management of renal failure on usual line.

• Anaphylaxis
• Delayed type of hypersensitivity reaction

Labels: Must know, Top