Toxicity of snakes

Sources:

ELAPID SNAKES : CORAL SNAKES

• Micurus spp., Micuroides spp.
• Brightly colored rings.
• Coral snakes: black snout and consist of small yellow.
• Nonvenomous snakes: red on black.

COLUBRID SNAKES:

Several species

• Sonoran lyre snake ( Trimorphodon lambda )
• Vine snake ( Oxybelisaeneus )
• King snake ( Lampropelitsspp. )
• Fixed fangs in rear of mouth
• Must ” chew ” on victims
• Not significant cause of envenomation.

CROTAILD SNAKES ( PIT VIPERS )

• Copperheads ( Agkistrodoncontortix )
• Found in eastern United States
• Water moccasins ( AgkistrodonPiscivorus )
• Also known as the cottonmouth
• Semiaquatic, found primarily in the southeastern United States
• Small rattlesnakes
• Pygmy rattlesnakes ( Sistrurusmiliaris )
• Massasauga ( sistruruscatenatus )
• Rattlesnakes ( Crotalus )
• Found throughout the United states.

Species:

• All species susceptible
• Dogs, cats and horse commonly envenomated species.
• Usually bitten on the nose and front legs.

                      Fig : cobra                                        

Fig: pit vipers

.

Fig : Coral snakes

Transmission : -By biting of poisoning snakes.

• By ingestion of contaminated food, water etc. with snake venom.

Toxic components :

• Complex mixture of amino acids, proteins, enzymes, proteins occur in snake venom.

Proteins : Large number of enzymatic and non-enzymatic proteins occur in snake venom.

a. Enzymatic proteins:

• Proteolytic enzymes ( e.g. protease )
• Hyaluronidase
• Phosphodiesterases
• ATPase
• Acetylcholinesterases
• Phospholipases A, B and c
• Lipases
• Ribonuclease
• Dexoyribonuclease
• Thrombin like enzyme

b. Non-enzymatic proteins: several low molecular weight peptides or polypeptides.

c. Non- proteins toxins:

 →Lipids, steroids, glycoproteins, amines, metals ( Na, Ca, k, Mg, Zn, Ni, Fe, etc. )

Toxicity : – Varies greatly with snake

• As many as 40% of strikes are dry bites no envenomation.

Mechanism of actions:

→ Enzymes in venom break down tissues.

• Spread of venom
• Production of edema at bite site.
• Spread to surrounding tissue.

• Neurotoxicity:

a. Post synaptic neurotoxins ( elapids & sea snakes )

                          ↓

Bind to cholinergic receptors in the neuromuscular junction

                          ↓

Antagonize the action of Ach on skeletal muscles

                          ↓

     Paralysis  ( Curare like effect )

b. Presynaptic neurotoxins ( elapids , Krait )

                       ↓

Block release of Ach at myoneural junction

                      ↓

               Block neurotransmission.

• HAEMATOTOXICITY:

a. Coagulopathy :

• Venoms increase or decrease coagulation through acting upon
• Fibrinogen or fibrinolytic enzymes
• Plasminogen activators
• Prothrombin activators
• Phospholipase inhibitors
• Factor X, V, IX or C activators
• Induce or inhibit platelet aggregation

b. Cardiotoxicity;

  increase capillary permeability

&

              decrease intravascular blood volume

                                ↓

                            Shock

c. Haemolysis :

• Haemorrhagins : hemolysis of RBC and decomposition of mucus membrane.
• Leucolysis : WBC destruction.

Clinical signs: –

1. Tissue damage
2. Hypotension and shock
3. Local edema

• Possibly progressing to regional swelling.
• Dyspnea if bites is on face or nose

4. Bleeding

• From bite site
• Ecchymosis
• Discoloration of the affected area

5. Hemoglobinuria or myoglobinuria

6. Pain

7. Respiratory failure

• More common with coral snake bites.

Diagnosis:

• History of biting by snake.
• Clinical signs and symptoms
• Clinical pathology:
• Complete blood cell count
• Platelet count
• Prothrombin time, partial thromboplastin time
• Fibrin degradation products
• Creatine kinase
• Urine dipstick for myoglobin.

Treatment :

EMERGENCY THERAPY:

a. Management of airway, breathing, circulation

• If a bite wound is on nose or if there is pronounced swelling of the larynx, tracheotomy is needed.

b. Fluid therapy:

• Crystalloids
• Two intravenous lines may be needed

c. Oxygen therapy

SPECIFIC THERAPY:

a. Fluid therapy:

• Maintain adequate volume of fluids to prevent cardiovascular collapse.
• Administer lactated Ringer solution, normal saline solution, or crystalloid.

b. Diphenhyldramine

• Sedation
• Pretreatment for anaphylaxis against antivenin.

ANTIVENIN THERAPY:

a. Polyvalent crotalidae antivenin

• Rattlesnakes
• Derived from horse serum ( possible anaphylaxis )
• Intradermal test before treatment.

b. Micrurusfulvis antivenin:

• Eastern or Texas coral snake
• Not effective fir bites of sonoran or western coral snake
• Not as readily available a crotalidae antivenin
• Horse derived product-hypersensitivity possible.
• Intradermal test before treatment.

SUPPORTIVE THERAPY:

a. Severe bleeding

• Prepare for transfusion.

b. Respiratory dysfunction

• Provide oxygen
• Provide mechanical ventilation if necessary
• Monitor oxygenation
• Perform pulse oximetry
• Measure arterial blood gases

c. Bite wound;

• Clean and lightly wrap

Differential diagnosis:

Pit viper bite include trauma, insects bites or strings, animal, bites, draining abscess and penetrating wound.