Snake Venom

Snake venom is animal poison. There are about 2500 species of snakes in the world, of which over 200 varieties are found in India. Some snakes are not poisonous or dangerously poisonous only about 50 of them are poisonous. Some of them like cobra, krait and viper are very poisonous. Snake venom is rarely used in for criminal purposes though there are reported cases where animals were poisoned by snake venom.

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Nature

Snake venom is a clear and transparent liquid. It is toxic even in the dry state.

Snake venom contains a number of poisonous materials which includes neurotoxins, haemotoxins, cardiotoxins, vasculotoxin and myotoxic which affects the body and its part in different ways. They have following toxic effects:

Neurotoxic effects– The venom affects the nervous system. The person feels weak, giddy and lethargic. The weakness slowly changes into paralysis.

Haemotoxic effects– The blood does not clot. The wound continue to bleed. The toxin lysine present in some venoms is responsible to lyse the protein, fibrinogen which is responsible for coagulation.

Cardiotoxic effect– The venom affects the cardiac system.

Vasculotoxic effects– This produces enzymatic destruction of cell walls and coagulation disorders. As a result, the endothelium of blood vessels is destroyed.

Myotoxic effects– This produces generalized muscular pain followed by myoglobinuria.

nature animal reptile snake

►Snake venom also has chemical composition consists of Toxins such as low molecular weight polypeptide and proteins, glycoproteins as well as Enzymes like proteinases, hydrolases, transaminase, hyaluronidase, cholinesterase, phospholipase, ATPase, ribonuclease, deoxyribonuclease

►Proteolytic enzymes cause tissue destruction by liberating histamines by damaging muscular epithelium of blood vessels leading to release of RBCs and serum in tissue.

►Phosphatidases cause haemolysis and toxic effects on heart and circulation.

►Neurotoxins produce curare-like effect on CNS leading to paralysis.

Classification of Venomous Snake:

Elapids- This group consists of cobra, king cobra, common krait, banded krait and coral.

  • The head is nearly of the same width as that of the neck.
  • Pupils are round.
  • The fangs are situated anteriorly but being covered with a fold of mucous membrane.
  • They are secreating neurotoxic venom.
  • They are short, fixed and grooved.
  • These types of snakes cannot bite through cloths or inject a complete dose.
  • The tail is usually round.

Vipers- This group consists of pit vipers and pitless vipers.

  • They are secreting vasculotoxin venom.
  • The pit is situated between the eye and the nostril and it helps to detect warm blooded prey in the dark.
  • The head is triangular and wider than the neck.
  • The pupil is vertical.
  • The fangs are long, movable and canalized like hypodermic needle.
  • These type of snakes can byte through cloths and give a complete dose.
  • The fangs are easy to see when erected but being too big, lie tucked up by the side of the upper jaw.
  • The bites of pit vipers are seldom fatal to human beings but the bites of pitless vipers are too dangerous.
  • The tail is usually tapering.
  • The bamboo snakes belong to pit vipers while the Russell’s viper belongs to piles vipers.

Sea Snakes– This group consists of Sea krait and Belcher’s sea snake.

  • They are secreting myotoxin venom.
  • They are found in the vicinity of sea- coasts.
  • They have small head.
  • They have flat rudder-like tail to help in swimming.
  • The nostrils are situated on the top of the snout and are valved to enable free breathing.
  • Their belly plates are not broad and they have dull and tuberculated scales on their back.
  • Their venom apparatus is delicate with very short fixed fangs which are situated posteriorly.
  • They generally do not bite.

Difference between Venomous and non-Venomous snake

TraitsVenomous Non-Venomous
Belly scales Large and covered with the entire width of the belly. Small and do not covered with the entire width of the belly.
Head scales Small Large
Fangs Long and canalized like hypodermic needle. Short and solid
Tail Compressed Not markedly compressed

Habits

Generally noctumalNot so
Bite Two fang marks with or without small marks of other teeth.A number of small teeth marks in a row.

Active Principle

Snake venom contains toxalbumins and other several toxic principles such as follows-

  • Fibrinolysins
  • Proteolysins
  • Neurotoxins
  • Cholinesterase
  • Haemolysins
  • Thromboplastin
  • Agglutinins
  • Cardiotoxins
close up photo of a blue snake

Fatal Dose

  • 15 mg of the dried cobra venom.
  • 20 mg of the viper venom
  • 6 mg of the krait venom
  • 8 mg of the saw-scaled viper venom.
  • The amount of dried cobra venom yield in one bite is about 200-250mg. The viper bite yield about 150-200 mg, the krait about 20 mg and saw-scaled viper about 25 mg.

Fatal Period

  • Death may occur instantaneously from shock due to fright.
  • Generally, death from cobra venom occurs within a few minutes to few hours and that from viper venom in a few days.
  • Sea snake bite is mostly not fatal.

Administration

  • Snake venom is dangerous when injected into blood stream.
  • It was administered through vagina and rectum.
  • It is more or less harmless when taken orally. It is due to this reason that some people suck out the snake venom. If there are injuries or ulcers in the mouth or in the food canal, one should not suck the venom as it can cause venom poisoning.

Sign and Symptoms

The exact nature of sign and symptoms varies with the type of snake and the site of the bite but the General symptoms of the snake venom poisoning ar as follows-

  • Burning pain
  • Swelling and inflammation at the site of bite.
  • Giddiness
  • Nausea
  • Vomiting
  • Lethargy
  • Bleeding from gums
  • Rapid feeble pulse
  • Dialated pupils
  • Muscular weakness
  • Spreading paralysis
  • Bite from krait may cause severe pain in the abdomen and convulsion after death.
  • Difficulty in breathing and swallowing
  • Respiratory failure
  • Blurred vision
  • External ophthalmoplegia
  • Paraesthesiae around the mouth
  • Hyperacusis
  • Myoglobinuria
  • Hyperkalaemia
  • Death may occur instantaneously due to shock.
  • Headache
  • Myalgia
  • Vertigo

Post Mortem Findings

  • Bite marks on the body of the deceased.
  • Haemolytic purple blood.
  • Local Necrosis.
  • There are haemorrhages in the lungs.
  • The blood is generally fluid and haemolysed causing early staining of the blood vessels.
  • Endocardial haemorrhages are seen especially in the left ventricle.
  • Petechiae are also found within the kidney pelvis and mucous of the urinary bladder, stomach and intestine.
  • Arterioles and capillaries are characterized by blurred walls and swollen endothelial cells.
  • Blood fails to clot normally even after addition of thrombin because of the extremely low level of fibrinogen.
  • Peeling of skin in some cases.
  • Oozing of the blood from the site of the bite especially in viper bite.

Antivenin

  • It is of 2 kinds either specific or polyvalent.
  • Specific antivenin is prepared by hyperimmunising horses against venom of a particular snake while polyvalent antivenin is prepared by hyperimmunising horses against the venoms of 4 common poisonous snakes such as cobra, common krait, Russel’s viper and saw-scaled viper.
  • Antivenin is very effective even when given after a delay, it is important to establish the necessity of its use.
  • Injection of antivenin if done at the site of the bite within a few minutes can help to ameliorate local necrosis.

General Measures

  • Stimulants are helpful in paralytic cases and artificial respiration is often required.
  • Transfusion of whole blood may be helpful in haemorrhagic cases.
  • Steroids are effective in combating the allergic manifestation of antivenin therapy.
  • Aspirin, short acting barbiturates and antibiotic prophylaxis are to combat secondary infection.
  • A patient bitten by an elapid snake if not dead in 2 hours will probably recover rapidly and completely.
  • A patient bitten by a viper is in danger for a much longer time and convalescence is very protracted.

Detection

  • Snake Venom is tested by injecting the extract in frogs with and without anti-venom serum. The frog without anti-serum should die and the other should survive.
  • The local washings from the site of bite are also useful for test.

Forensic Examination

  • Complete blood count—leucocytosis may be evident with thrombocytopenia.
  • Smear — hemolysed and fragmented RBCs.
  • Increased prothrombin time and increased partial thromboplastin time.
  • Immunodiffusion
  • Counter-current immunoelectrophoresis.
  • Enzyme -Linked Immunoassay (ELISA)
  • Radioimmunoassay (RIA)

Autopsy Materials

  • Skin around the bite.
  • Blood
  • Kidney

Medicolegal Findings

● Snake bite is generally accidental, rarely homicidal and still rarely suicidal.

● In some homicidal cases, where the death is alleged to be form from snakebite the presence of snake venom may have to be checked.

● Deaths from accidental snake bites are frequent in warm and moist climates.

● Cattle are sometimes poisoned by cobblers for the sake of hides by a peculiar method.

● A cobra is placed in an earthen vessel with a banana. The cobra is irritated by applying heat to the vessel. It bites the fruit, the pulp of which is then smeared on a rag and the rug thrust in the animal’s rectum with the help of a bamboo stick.

● Sui (abrus precatorius) poisoning of cattle resembles viperine snake bite.

References

  1. Dr. K.S. Narayan Reddy. The essential of forensic medicine and toxicology.34th edition.
  2. VV Pillay. Modern medical toxicology.4th edition.
  3. R.K.Sharma. Concise textbook of forensic medicine and toxicology. 3rd edition.
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