There are 2500 species of snakes in the world.
• Only 200 species are present in Pakistan.
Snakes are divided into two major groups
• Poisonous snakes
• Nonpoisonous snakes
Classification of Poisonous snakes
• Neurotoxic(elapid)
• Vasculotoxic(vipers)
• Myotoxic(sea snakes)
Neurotoxic
• cobra
• king cobra
• Krait
• coral
Vasculotoxic
• Pit vipers
• non pit vipers
• Russell’s vipers
• Saw scaled vipers
Myotoxic
• True sea snake
• Sea krait
Anatomy of Snakes
Characteristic anatomical features include
• Shape of head
• Pupils
• Nostrils
• Tail
• Upper and lower jaws contain teeth
Fangs along with small teeth two or
more fangs may be present ,which are
specialized,canulated teeth used to inject
venom in to prey. Fangs are connected to the
salivary glands,which produce saliva that is
poisonous for other animals and human beings .
Identification of Poisonous snakes
Elapid
• Head has the same width as that of neck.
• Pupils are rounded.
• Fangs are short , fixed and grooved.
vipers
• Pit-less vipers are more dangerous than pitted
ones.
• Head is triangular and wider than neck.
• Pupils are vertical
• Fangs are long , moveable and canalized.
Sea snake
• Head is small
• Tail is flat
• Fangs are short and fixeds
Snake venom
• Venom is the toxic saliva produced by the parotid salivary galnds of the poisonous snakes.
Composition
• Fibrinolysins • Proteolysins • Neurotoxins • Cholinestarses • Haemolysins • Thromboplastin • Agglutinins • Cardiotoxins • Hyaluronidas
Mode of action
Elapids
they produce neurotoxic poisons .Their acts on motor nerve cells and acts in a similar manner to tubocurarine poison i.e. compete with acetylcholine at nicotinic receptors, rendering acetylcholine inactive thus leading to muscular weakness especially of legs that progress to generalized paralysis.
vipers
Vipers produce vasculotoxic poison .
Venom produces enzymatic destruction of cell membranes and coagulation disorders. These actions result in
• Destruction of endothelial cells of blood vessels
• Lyses of RBCs
• Failure of blood clotting
Sea snakes
They produce myotoxic poison Venom produces
• Muscular pains
• Myoglobinuria
• respiratory failure due to muscular weakness.
Symptoms and signs
vasculotoxic
•Local effects
• Fang mark at the site of injection.
• Intense local pain.
• Swelling.
• Oozing out of haemolyzed blood.
• Blisters may appear.
General effects
• Haemoglobinuria • Petechial haemorrhages • Bleeding from gums, mucus membranes such as rectum and body orifices • Haemoptysis • Cold, clammy skin • Death due to circulatory failure
Myotoxic
• Four fang marks are present • At the site of bite no pain and swelling • Muscle weakness • Ptosis develops • Generalized muscle paralysis • Urine is brown in colour • Respiratory muscle weakness leads to death • Hyperkalemia may result in cardiac failure
Neurotoxic
•Local effects • Two fang marks • Slightly burning pain
General effects
• Neurotoxic effects lethargy , giddiness , muscular weakness and spreading paralysis
• Increased salivation and vomiting
• Ptosis and paralysis of extra ocular muscles
• Breathing becomes slow and laboured
• Patient remains conscious but unable to speak
• Finally respiratory paralysis consequently death
Fatal dose
4mg of krait venom • 16mg of dried venom of cobra • 40mg of viper venom
Fatal period
Death occurs within few min to few to few hours in cobra poisoning and few says in viper poisoning
TREATMENT
Steps of Treatment
• Shifting the victim to medical aid center • Allaying anxiety and fright • Prevention of spread of venom • Use of antivenin
Allaying anxiety and Fright
To prevent the shock due to fright it is desirable to reassure the victim by clarifying that
• All snakes are not poisonous
• Even poisonous snakes are not fully charged with poison all the time
• Even a snake with fully charged with poison does not always inject it’s lethal dose
Prevention of spread of Venom Through
• Immobilization
• Application of tourniquet
• Cleaning the wound
• Local emetine injection
• Incision and suction at the site
Use of Antivenin
Types of antivenin
• specific antivenin
• polyvalent antivenin strength of polyvalent antivenin is 1ml will neutralize 0.6mg of dried cobra venom 0.45mg of dried krait venom,0.6mg of dried russel’s viper venom and 0.45mg of dried sawscaled viper venom
Neutralize Toxin at Tissue Level
• Neostigmine and atropine administration in elapid snakebite.
• Heparin and fibrinogen in viper snakebite.
General Measures
• Artificial respiration • Blood Transfusion • Steroids • Antihistamines • Antibiotics • Stimulants are helpful in paralytic cases • Aspirin short acting barbiturates
Postmortem Appearance
• One or two bite marks.
• Some swelling and cellulitis about the bitten part.
• In case of neurotoxic venom signs of asphyxia.
• In case of viper bite local appearances are a more striking due to severe oozing of blood from puncture site.
• Haemorrhages in the lungs and in the serous membranes.
• Endocardial haemorrhages are seen especially in left ventricle.
• Petechiae are also found within the kidney pelvis,and mucosa of urinary bladder,stomach, and intestines.
• Blood fails to clot normally even after addition of thrombin.
• Arterioles and capillaries are characterized by blurred walls and swollen endothelial cells.
• Necrosis of renal tubules and cloudy swelling and granular changes in the cells of other organs.
Contraindications
• Morphine and alcohol as these depresses respiratory center
Medicolegal Importance
• Generally accidental • Rarely homicidal • Still rarely suicidal
