Overview
Snakebite envenoming is what happens when a venomous snake injects venom through a bite. WHO describes it as a neglected public health problem that can cause paralysis stopping the breathing, bleeding that cannot be controlled, kidney failure and tissue destruction leading to amputation.
WHO estimates between 81 410 and 137 880 deaths a year, with about three times as many permanent disabilities. Antivenom works, and WHO states most of these deaths are entirely preventable.
Disease Summary
- Category
- Non-Communicable Disease
- Cause
- Venom injected by a venomous snake
- Transmission
- Not transmissible. Caused by a snake bite
- Body System
- Multiple organ systems
- Preventable
- Yes
- Curable
- Yes
Symptoms
Common Symptoms
Not every bite injects venom. Symptoms depend on the snake, and they can begin immediately or over several hours.
Puncture Marks at the Bite
CDC lists puncture marks as the first local sign, though they are not always obvious.
Swelling, Bruising, Blistering and Bleeding at the Bite
CDC lists all of these among the local effects of a venomous bite.
Severe Pain and Tenderness
Listed by CDC. Some bites, particularly from sea snakes, cause little pain and are still dangerous.
Nausea, Vomiting or Diarrhoea
Listed by CDC among the effects that spread beyond the bite site.
Blurred Vision or Drooping Eyelids
CDC attributes these to nerve-acting venoms, along with numbness, difficulty swallowing and weakness.
Irregular Heartbeat and Low Blood Pressure
Both are listed by CDC among the effects that reach the whole body.
A Metallic or Rubbery Taste
CDC lists this distinctive symptom, which some people notice early.
Numbness, Tingling and Muscle Twitching
CDC lists numbness or tingling around the face or limbs together with muscle twitching.
Danger Signs
Seek urgent medical attention immediately if any of the following symptoms develop.
Difficulty Breathing, Drooping Eyelids or Difficulty Swallowing
WHO states bites can cause severe paralysis that prevents breathing. This is an airway emergency and needs immediate hospital care.
Bleeding That Will Not Stop
From the bite, the gums, the nose or in the urine. WHO states bleeding disorders can lead to fatal haemorrhage.
Passing Little or No Urine
WHO states that snakebite can cause irreversible kidney failure.
Rapidly Spreading Swelling, Blistering or Darkening of the Limb
WHO states tissue damage can cause permanent disability and limb amputation.
Collapse, Low Blood Pressure or an Irregular Heartbeat
These indicate the venom is affecting the circulation and are an emergency.
Drowsiness or Vomiting With Weakness
WHO advises placing the person on their left side in the recovery position to protect the airway, which indicates how dangerous this combination is.
Diagnosis
The Bite and the Local Signs
Puncture marks with swelling, bruising, blistering and severe pain point to a venomous bite. CDC advises photographing the snake safely if possible, without attempting to catch it.
Recognising the Pattern of Envenoming
CDC separates nerve-acting effects, such as blurred vision, paralysis and difficulty breathing, from blood and muscle effects, such as bleeding and tissue destruction. The pattern guides treatment.
The Bedside Clotting Test
WHO names the 20 minute whole blood clotting test as the bedside test that confirms the clotting failure requiring antivenom.
Watching and Recording the Swelling
CDC advises marking the leading edge of the swelling and recording the times, so that progression can be seen.
Recognising a Bite With No Venom
WHO notes that many bites do not inject venom, so assessment must distinguish these from bites that need antivenom, using the evolving signs and the clotting test.
Laboratory Tests
20 Minute Whole Blood Clotting Test
WHO states this test confirms the clotting failure requiring antivenom. Blood that has not clotted after 20 minutes in a clean dry glass tube indicates venom has disrupted clotting.
Full Blood Count
Falling platelets and haemoglobin support venom-induced bleeding and guide the need for transfusion.
Kidney Function Tests and Urine Test
Rising kidney values or dark urine indicate the kidney failure WHO lists among the effects of envenoming.
Muscle Enzyme Test
A high level indicates muscle breakdown, which threatens the kidneys and changes treatment.
Blood Group and Cross-Match
Prepares for transfusion if bleeding is severe, and for surgery if tissue damage requires it.
Treatment
Antivenom
WHO states that antivenom is the most effective treatment for life-threatening snakebite and the only specific treatment that can prevent or reverse most of the effects. WHO stresses timing, because many of the effects of venom are irreversible once established.
Breathing Support
WHO lists artificial respiration among supportive treatments. It keeps a paralysed person alive while the antivenom works.
Medicines to Restore Muscle Function
WHO states that anticholinesterase medicines can restore nerve and muscle function in bites from snakes with nerve-acting venom.
Dialysis
WHO lists kidney dialysis among supportive treatments for the kidney failure venom can cause.
Wound Care, Surgery and Rehabilitation
WHO states that tissue-destroying, muscle-damaging or bleeding effects require prolonged hospital treatment and extensive rehabilitation, including reconstructive surgery and prostheses where limbs are lost.
Prevention
Wear proper footwear and long trousers
WHO notes that 80% of bites occur below the knee, which makes boots the single most effective protection for farm and bush work.
Keep grass short around homes and paths
WHO advises keeping grass short near homes and pathways so that snakes have less cover close to where people walk.
Use a light at night
Many bites happen to people walking or working after dark. A torch lets you see where you are putting your feet.
Seal houses and store food securely
Snakes follow rodents, and rodents follow stored grain. Sealing gaps and storing food properly removes the reason for a snake to enter.
Sleep on a raised platform under a tucked-in net
WHO advises raised sleeping platforms with nets tucked in, because bites to people sleeping on the ground are common and often severe.
Never try to catch, kill or handle a snake
CDC warns against handling any venomous snake, including a dead one or a severed head, which can still bite reflexively.
Risk Factors
Rural Agricultural Workers and Their Families
WHO names this group first among those affected.
- Farmers working in fields, especially at planting and harvest
- Herders and fishermen
- People walking to fields or water before dawn or after dusk
- People living in poorly constructed houses
Children
WHO states that children often suffer more severe effects than adults.
- Children have a smaller body mass, so the same amount of venom does more harm
- Working children in agricultural households
- Children playing in long grass or around stored grain
- Children sleeping on the floor rather than a raised bed
People Far From Antivenom
Distance from treatment is one of the strongest determinants of outcome.
- Communities hours from the nearest facility holding antivenom
- Areas where antivenom is unaffordable or out of stock
- People who try traditional remedies first and arrive late
- Places without transport at night
Complications
Paralysis and Breathing Failure
WHO states that bites can cause paralysis that prevents breathing, which is a leading cause of death.
Uncontrolled Bleeding
WHO states that bleeding disorders can lead to fatal haemorrhage.
Kidney Failure
WHO states that snakebite can cause irreversible kidney failure, which may require dialysis.
Tissue Destruction and Amputation
WHO states that tissue damage can cause permanent disability and limb amputation.
Long-Term Disability
WHO estimates around three times as many permanent disabilities as deaths each year.
Psychological Consequences
WHO includes rehabilitation and support in its treatment framework, recognising that the effects are not only physical.
When to Seek Medical Care
Immediately After Any Snake Bite
Go to a health facility straight away, whether or not symptoms have started. CDC states not to delay medical attention waiting for symptoms.
Any Difficulty Breathing, Swallowing or Speaking
These indicate the venom is affecting the nerves and muscles and the airway is at risk.
Any Bleeding That Will Not Stop
From the bite, gums, nose or in urine or stool.
Passing Little or No Urine
This indicates the kidneys are affected and needs urgent assessment.
Rapidly Spreading Swelling or Darkening of the Limb
This indicates tissue destruction and the limb may be at risk.
Prognosis
Antivenom Given Early Changes Everything
WHO states that antivenom can prevent or reverse most of the effects when given early at adequate doses.
Delay Costs Function
WHO states that many of the effects of venom are irreversible, so late treatment leaves permanent damage even when it saves life.
Recovery From Paralysis Is Usually Complete
Where breathing support is available through the paralysed period, people generally recover nerve and muscle function fully.
Disability Is Common
WHO estimates around three times as many permanent disabilities as deaths, including amputations, contractures and scarring.
Differential Diagnosis
A Bite From a Non-Venomous Snake
Causes puncture marks and anxiety but no progressive swelling, no bleeding and a normal clotting test.
A Dry Bite From a Venomous Snake
WHO notes that many bites do not inject venom. These are separated by watching for signs and by the clotting test, in a health facility.
Scorpion Sting or Other Envenoming
Causes severe local pain and systemic effects, and is separated by what the person saw and by the pattern of symptoms.
Wound Infection
Develops over days with fever and spreading redness, rather than the immediate swelling of envenoming.
Panic and Anxiety After a Bite
Causes rapid breathing, tingling and light-headedness. It is real distress, but the clotting test and observation separate it from envenoming.
References
World Health Organization: Snakebite envenoming
WHO fact sheet on the burden, the effects of venom, treatment and the antivenom supply problem.
World Health Organization: Snakebite envenoming, questions and answers
WHO guidance on first aid, what to avoid, and practical prevention measures.
World Health Organization: Snakebite envenoming treatment and rehabilitation
WHO guidance on antivenom, supportive treatment, the bedside clotting test and rehabilitation.
CDC: Venomous Snakes at Work
Signs of envenoming, first aid steps and what not to do after a bite.
Frequently Asked Questions
What is the first thing to do after a snake bite?
Move away from the snake, remove rings, watches and anything tight near the bite before swelling starts, keep the person still and splint the bitten limb, place them on their left side, and get them to a health facility urgently, carrying rather than walking them. WHO also advises reassuring them, because many bites do not inject venom.
Should I cut the wound or suck out the venom?
No. WHO lists cutting, suction, tight tourniquets, black stones, herbal remedies and chemicals among methods that must not be used, and states they are dangerous as well as ineffective and waste valuable time. CDC adds not to apply ice, use electric shock, drink alcohol or take aspirin or ibuprofen.
Does every snake bite need antivenom?
No. WHO notes that many bites do not inject venom. Whether antivenom is needed is decided at a health facility, based on the signs that develop and on the 20 minute whole blood clotting test. That decision cannot safely be made at home.
Should I try to catch or kill the snake?
No. CDC warns never to handle a venomous snake, including a dead one or a severed head. If it can be done safely and without delay, a photograph from a distance can help identification, but getting to hospital matters far more.
How dangerous is snakebite in Africa?
WHO estimates between 435 000 and 580 000 bites needing treatment in Africa each year. Globally WHO estimates between 81 410 and 137 880 deaths annually, with around three times as many people left with permanent disability. WHO states most of these deaths are entirely preventable with available antivenom.