Venomous bites and stings

Snake bites and envenomation

– More than 50% of the bites are dry bites, i.e. no envenomation occurred. In the event that venom is injected, the severity of envenomation depends on the species, the amount of venom injected, the location of the bite (bites on the head and neck are the most dangerous) and the weight, general condition and age of the individual (more serious in children).

– It is rare that the snake involved is identified. However, observation of the clinical signs may orient diagnosis and management. Two major syndromes are identified:
• neurological disorders that evolve towards respiratory muscle paralysis and coma are common manifestations of elapid envenomation (cobra, mamba, etc.);
• extensive local lesions (intense pain, inflammation with oedema and necrosis) and coagulation abnormalities are common manifestations of viperid or crotalid (rattle snake) envenomation.
Clinical manifestations and management of bites and envenomations are described in the table below.

– Early diagnosis and monitoring of coagulation abnormalities is based on whole blood clotting tests performed in a dry tube (at the patient’s arrival and then every 4 to 6 hours for the first day).
Take 2 to 5 ml of whole blood, wait 30 minutes and examine the tube:
• Complete clotting: no coagulation abnormality
• Incomplete clotting or no clotting: coagulation abnormality, susceptibility to bleedi1
In the event of coagulation abnormalities, continue to monitor once daily until coagulation returns to normal.

– Aetiological treatment is based on the administration of snake antivenom serum, only if there are clear clinical manifestations of envenomation or coagulation abnormalities are observed.
Antivenom sera are effective, but rarely available (verify local availability) and difficult to store. Antivenom serum should be administered as early as possible: by IV infusion (in 0.9% sodium chloride) if using a poorly purified serum; by slow IV in the event of severe envenomation if the serum is known to be well purified. Repeat antivenom serum administration after 4 or 6 hours if the symptoms of envenomation persist.

 For all patients, be prepared for an anaphylactic reaction, which, despite its potential severity (shock), is usually more easily controlled than coagulation disorders or serious neurological disorders.

– In asymptomatic patients (bites without signs of envenomation and with normal coagulation), monitoring must continue for at least 12 hours (24 hours preferred).

Clinical signs and treatment

Time since bite

Clinical manifestations

Possible aggressor

Treatment

Bite

0

Fang marks
Pain at the site of bite

?

Strict rest, immobilisation of the limb with a splint to slow the diffusion of venoma.
Wound cleansing.
Tetanus prophylaxis (Tetanus, Chapter 7).
Observe for manifestations of envenomation. A the dispensary level, prepare patient evacuation to a referral centre.

Envenomation

10-30 minutes

Hypotension, myosis, excessive salivation and sweating, dysphagia, dyspnoea
Local paraesthesia, paresis

Elapids

Insert a peripheral IV line.
IV antivenom serum as soon as possible.

Inflammatory syndrome: intense pain, extensive regional oedema

Viperids Crotalids

Insert a peripheral IV line.
IV antivenom serum as soon as possible.
Analgesicsb.
IV or POb anti-inflammatories.

30 minutes-
5 hours

Cobra syndrome: bilateral eyelid drooping, trismus, respiratory muscle paralysis
Shock

Elapids

Intubation and assisted ventilation.
See Shock, Chapter 1.

30 minutes-
48 hours

Haemorrhagic syndome: epistaxis, purpura, haemolysis or disseminated intra-vascular coagulation
Shock

Viperids Crotalids

Monitor coagulation (blood clotting test in a dry tube).
Transfusion of fresh blood in the event of severe anaemia.
See Shock, Chapter 1.

6 hours
or more

No signs or changes in coagulation (non-venomous snakes or snake bite without envenomation)

?

Reassure the patient.
Send him home after 12 hours.

Tissue necrosis


Remove blisters, clean; daily (non occlusive) dressings.
Surgical intervention for necrosis, depending on the extent, after the lesions stabilise (minimum 15 days).

a  Tourniquets, incision-suction and cauterisation are ineffective and may be dangerous.
b  Do not use acetylsalicylic acid (aspirin).

– In case of clinical evidence of infection only: drainage of any abscess; amoxicillin/clavulanic acid (co-amoxiclav) for 7 to 10 days in case of cellulitis.
Infections are relatively rare, and most often associated with traditional treatment or with nosocomial transmission after unnecessary or premature surgery.

Scorpion stings and envenomation

– In most cases, the sting causes local effects including: pain, oedema, erythema. Management includes strict rest, wound cleansing, analgesics PO, and tetanus prophylaxis (see Tetanus, Chapter 7).
In patients with significant pain, infiltrate the area around the sting with local anaesthetic (1% lidocaine). Observe for 12 hours.

– General signs appear in the event of severe envenomation: hypertension, excessive salivation and sweating, hyperthermia, vomiting, diarrhoea, muscle pain, respiratory difficulties, seizures; rarely, shock.

– Aetiological treatment:
The use of scorpion antivenom sera is controversial (most of them are not very effective; they may be poorly tolerated due to insufficient purification).
In practice, in countries where scorpion envenomations are severe (North Africa, the Middle East, Central America and Amazonia), check local availability of antivenom sera and follow national recommendations.
The criteria for administration are the severity of the envenomation, the age of the patient (more severe in children) and the time elapsed since the sting. This should not exceed 2 to 3 hours. If the time elapsed is more than 2 or 3 hours, the benefit of antivenom serum is poor in comparison with the risk of anaphylaxis (in contrast to envenomation by snakes).

– Symptomatic treatment:
• In the event of vomiting, diarrhoea or excessive sweating: prevention of dehydration (oral rehydration salts), especially in children.
• In the event of muscle pain: 10% calcium gluconate slow IV (children: 5 ml per injection, adults: 10 ml per injection, administered over 10 to 20 minutes).
• In the event of seizures: diazepam may be used with caution; the risk of respiratory depression is increased in envenomated patients (see Seizures, Chapter 1).

Spider bites and envenomation

– Treatment is usually limited to wound cleansing, strict rest, analgesics PO and tetanus prophylaxis (see Tetanus, Chapter 7).

– Severe envenomations are rare. There are two main clinical syndromes:

• Neurotoxic syndrome (black widow spider): severe muscle pain, tachycardia, hypertension, nausea, vomiting, headache, excessive sweating. The signs develop for 24 hours and then resolve spontaneously over a few days.

• Necrotic syndrome (recluse spider): local tissue lesions, possible necrosis and ulceration; mild general signs (fever, chills, malaise and vomiting) which usually resolve over a few days. If present, haemolysis may sometimes be life threatening.

As well as the general measures listed above, treatment includes administration of 10% calcium gluconate by slow IV in the event of muscle spasms (children: 5 ml per injection, adults: 10 ml per injection, administered over 10 to 20 minutes).
Incision and debridement of necrotic tissue are not recommended (not useful; may impair healing).

Hymenoptera stings (honeybees, wasps and hornets)

– Local care: remove the embedded sting (bee); clean with soap and water; calamine lotion if pruriginous (children and adults: one application 3 to 4 times daily in a thin layer).

– Analgesics if necessary (paracetamol PO).

– In the event of an anaphylactic reaction:
epinephrine (adrenaline) IM
Use undiluted epinephrine solution (1:1000 = 1 mg/ml) and a 1 ml syringe graduated in 0.01 ml in children:
Children under 6 years: 0.15 ml
Children from 6 to 12 years: 0.3 ml
Children over 12 years and adults: 0.5 ml

For children, if 1 ml syringe is not available, use a diluted solution, i.e. add 1 mg epinephine to 9 ml of 0.9% sodium chloride to obtain a 0.1 mg/ml solution (1:10 000):
Children under 6 years: 1.5 ml
Children from 6 to 12 years: 3 ml

Repeat after 5 minutes if no clinical improvement.

In patients with circulatory collapse or those who deteriorate despite receiving IM epinephrine, use IV epinephrine (for doses, see Anaphylactic shock, Chapter 1).



Footnotes
Ref Notes
1 There can be a considerable delay between the decrease in coagulation factors (less than 30 minutes after the bite) and the first signs of bleeding (other than bleeding at the site of the bite and/or the development of sero-sanguinous blisters), which may appear only 3 days after the bite. Conversely, bleeding may resolve prior to normalization of coagulation parameters.