Signs and symptoms of snake bite

Dr.Debasish Datta, Ex Emergency Medical officer
Read time: 6 minutes
Signs and symptoms of snake bite can be discussed under the following headings.
A) Signs and symptoms due to fear 
B) Signs and symptoms due to traditional first aid 
C) Signs and symptoms due to venom of the snake.

Signs and symptoms due to fear-

 
Some people become very anxious when they are bitten by a snake or suspect that they are bitten by a snake. By thinking about the potency and consequences of venom, they become very frightened which may lead to different types of signs and symptoms though they are not bitten by a venomous snake.
It is important to know these signs and symptoms because the appearance of these signs and symptoms do not necessarily indicate poisonous snake bite and in fact may mislead everyone including medical personnel when they are admitted in a hospital.
These may be-
1)Overbreathing 
2) Paralysis, stiffness, tetany or paresthesia ( altered sensations in limbs, mainly pin and needles paresthesia )
3) Excessive slowing of heart rate may cause dizziness or vasovagal attack ( faintness and collapse).
4) In some patients blood pressure and heart rate may increase causing palpitation.
5) There may be sweating, tremor, vomiting and diarrhoea.
6) Even the patient may die due to extreme fear.

Signs and symptoms due to traditional first aid- 

1) Application of tourniquet in bitten limb may cause local swelling, pain, congestion ( abnormal accumulation of blood and fluid locally) that may mimic local envenomation by some venomous snakes.
2) incision at the bitten site may cause bleeding mimicking hematotoxic snake bite.
3) Ingestion of herbal remedies can cause gastrointestinal symptoms such as nausea, vomiting, diarrhoea and also other symptoms according to the remedy.

Signs and symptoms due to venoms of the snake-

Snake venoms are mainly of three types 
Neurotoxic
Hematotoxic and
Myotoxic. 
Venom from a particular snake species may contain one or more than one type of toxin. Symptoms of snake bite depend upon the type of the venom. Symptoms may be
A)  Local ( signs and symptoms at the site of snake bite ) or
B) Systemic ( signs and symptoms that may be occur in whole body or other parts of the body)

Signs and Symptoms of Neurotoxic snake bite-

Neurotoxins are mainly present in the venom of Cobra, Krait, Coral snakes and Mamba. 
Sea snake venom contains Myotoxin & Neurotoxin. 
Viper venoms are mainly Hemotoxins but some Vipers such as Russell’s viper venom contains some Neurotoxins so there may be some neurotoxic features in case of Russell’s viper bite.

A ) Local Signs and symptoms of Neurotoxic snake bite-

There may be fang marks. Fang marks may be one or more. Usually fang marks are punctured or abrasion wounds.
Local pain, tenderness & swelling gradually extending proximally up the bitten limb. Subsequently there may be blister formation, infection, abscess formation and gangrene of the affected limb which may lead to loss of the limb or may necessitate amputation. 
Tender proximal local lymph nodes & lymphangitis – Femoral lymph nodes ( lymph nodes in upper thigh), inguinal lymph nodes ( lymph nodes in groin) may be involved in case of lower limb bite.
Elbow ( epitrochlear) and axillary Lymph nodes in upper limb bite may be involved.
Due to the presence of cytotoxins cobra bites are extremely painful and cause local swelling (except Fillipine cobra where there is no or little local swelling or pain). 
Krait and sea snake bites are virtually painless even, the victim may not understand that he or she is beaten by a snake until other symptoms appear.
Spitting cobra venom may cause blindness if contacted with eyes & are not washed immediately.

B) Systematic Signs and symptoms of Neurotoxic snake bite-

Neurotoxicity in case of neurotoxic snake bite is descending in nature that is it starts from above spreading downwards in the body. 
First  neurotoxic feature is bilateral ptosis (dropping of both upper eyelids due to 3rd cranial nerve paralysis). Patient gradually becomes unable to open eyes & tries to open eyelids by using forehead muscles therefore there is furrowing of forehead.
There may be  diplopia (that is, the patient sees one item to be two due to paralysis of 3rd, 4th and 6th cranial nerves).
Patient may not be able to move eyes in different directions due to paralysis of eye muscles (External ophthalmoplegia) and can see in different directions only by turning his head in that direction. 
Patient may feel difficulty in speech (dysarthria ), impairment of voice (dysphonia) or complete loss of voice ( aphonia ).
Patient may feel difficulty in swallowing (dysphagia). As a result the patient can not swallow. Secretions  accumulate in the mouth and there may be aspiration or regurgitation through the nose. 
Gradually the patient becomes drowsy and very much sick looking. 
Due to weakness of respiratory muscles  there may be breathlessness (dyspnoea). 
Due to paralysis of different muscles there is generalized flaccid paralysis. 
Krait bites may sometimes present with low back pain or pain in the abdomen and vomiting.
Eventually the patient may die of respiratory failure. 

Signs and symptoms of Hematotoxic snake bite –

 
Viperids  venom mainly contains Hemotoxins. Though some elapid venoms contain some amount of Hemotoxins in addition to Neurotoxin. 

A) Local signs and symptoms of viper venom-

There is severe local reaction. fang mark, local pain and tenderness, local swelling gradually extending proximally, lymphangitis and proximal lymph node enlargement and tenderness.
Bruising and bleeding from site of bite. Blister formation, gangrene formation occur, which may lead to loss of the limb or may necessitate amputation.

B) Systematic signs and symptoms of viper bite–

There may be fall in blood pressure, faintness and collapse, damage of heart muscles and cardiac arrhythmia (irregular heart beat). 
There is failure of normal coagulation leading to hemorrhage from different sites of the body including  the site of bite, partially healed wound and venipuncture site (site where intravenous needle is introduced for administration of drugs or intravenous fluid) . 
Vomiting of blood (haematemesis), Bleeding from nose ( epistaxis ), gum, lungs (hemoptysis), through urine (hematuria) & per rectal bleeding, malena ( Black tarry stool) and per vaginal bleeding, bleeding from eyes, bleeding of different sizes  within the skin may occur.
There may be  cerebrovascular accident due to haemorrhage or thrombosis within the brain.
Meningism (characterized by neck stiffness, intolerance to bright light), headache due to subarachnoid hemorrhage. 
Increased capillary permeability may cause oedema in face & conjunctiva, pulmonary oedema, effusion in pleural and pericardial spaces. 
There may be pain in the abdomen.
There may be acute renal failure. 

Signs and symptoms of sea snake bite- 

Sea snake venom mainly contains myotoxins in addition to Neurotoxin. In case of sea snake bite there is little or no local sign. Even the patient may not be aware of the bite. 
Signs and symptoms usually occur within 30 minutes to 2 hours after the bite. 
Low blood pressure, ptosis, dysphagia, dizziness, blurred vision, excessive saliva production, nausea, breathing difficulties and respiratory failure may occur.
Muscle pain, weakness or paralysis. Paralysis of limb, joint pain.
Myoglobinuria. 
Progressive renal failure may occur.

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