Clinical Toxicology - Venomous Animals

Acute poisoning by venomous animals is common in tropical and subtropical climates.
Precise chemical composition and pathophysiology of animal venoms are incompletely known, limiting specific treatment options.
General principles of intensive supportive therapy should be followed in managing these poisonings.

Snake Bites

Over 3,000 snake species worldwide, but only about 250 are venomous.
Venomous snakes are categorized by fang type:
- Viperids (foldable fangs)
- Elapids (fixed fangs)
Examples of venomous snake families
- Rattlesnakes
- Saw-scaled vipers
- Cobras
- Mambas
- Sea snakes
Snake bites often occur in children or adults disturbing snakes.
Snake venom contains enzymes, non-enzymatic proteins, and other substances such as acetylcholine and 5-hydroxytryptamine.
Venom effects can trigger tissue inflammation (kinins, histamines, slow reacting substance).
Severity of snake bite depends on venom type and quantity injected, age, size, and sex of the snake.
Bites occurring at night tend to be more venomous than those during the day and in hibernating snakes the venom is more potent after hibernation.
Venomous snake bites usually leave two (occasionally one) fang marks. Non-poisonous snake bites produce a semi-circular set of tooth marks.
Local effects: mild inflammation, slight bruising, and potentially tissue necrosis (especially in Viperidae and Crotalidae bites). Necrosis often occurs several days after bite, preceded by pain and swelling.
Systemic effects: nausea, vomiting, hypotension due to vasodilation and hypovolemia, drowsiness, muscular weakness leading to diplopia, speech difficulty, swallowing problems. Severe cases may include ventilatory paralysis, coma, and convulsions. Sensory function usually remains normal.
Haematological system: increased blood coagulability (rattlesnakes), prolonged coagulation defect with ecchymoses and bleeding tendency (Malayan Pit Viper), low plasma fibrinogen, and sea snake bites can cause marked polymyositis, elevated muscle enzymes, plasma potassium, and myoglobinuria with potential renal failure. Patients may experience weakness for months.

Treatment of Snake Bites

Popular misconceptions about snake bite management include using bands, incisions, and suction; these practices are not supported by evidence and may be harmful.
Cooling, antihistamines, and corticosteroids are not effective treatments for snake bites and thus should be avoided.
Recommended snake bite treatment:
- Careful cleansing of the wound with sterile saline.
- Immobilisation for local effects.
- Intensive supportive therapy.
- Injection of tetanus antitoxin (and booster dose of tetanus toxoid if needed).
- Injecting crystalline penicillin.
- Sedation and analgesic (as needed).
- Antivenins (if available and systemic effects are severe).

Insect Bites

Stings from ants, bees, wasps, and hornets usually cause local pain and swelling.
Respiratory distress may occur if stings are on the mouth or tongue.
Deaths are rare from insect stings but can occur with very extensive stings.
Severe allergic reactions, especially to bee stings, are more common.
Bee stings are alkaline while wasp and hornet stings are acid.
Treatment for bee stings or insects:
- Remove any remaining tentacles promptly.
- Use antihistamines systemically.
- In severe allergic reactions, inject S.C adrenaline 1:1000 (0.5ml) and hydrocortisone 100 mg I.V.

Spider Bites

Poisonous spiders are found in warm climates, with the Black Widow and Funnel-web spiders being common causes of bites.
Spiders are often found in outhouses, basements, and around houses. Children are often the victims.
Spider bites sometimes lead to death cases in young victims.
Initial bite may be initially unnoticed.
Symptoms include:
- Generalized pain.
- Muscle stiffness, burning sensation.
- Nausea, vomiting (abdominal rigidity may lead to misdiagnosis of peritonitis).
- Salivation, pyrexia (fever), sweating.
- Leucocytosis, mild hypertension, macular rash.
Treatment for spider bites:
- Cleanse bite with sterile saline or water.
- Administer analgesics for pain relief.
- Provide 10-20ml 10% calcium gluconate IV.
- Initiate systemic antibiotics if secondary infection occurs.
- Intensive supportive therapy as needed.

Scorpion Stings

Nocturnal creatures living in tropical or subtropical regions.
Sting is rarely fatal.
Symptoms after scorpion sting are marked local pain, followed by sweating, numbness, hyperaesthesia. Severe cases may cause central respiratory and cardiac depression.
Treatment for scorpion stings:
- Cleanse the sting.
- Administer analgesics for pain.
- Intensive supportive care as needed.

Venomous Sea Animals - Sting Rays

Sting rays are found in warm seas.
They present a hazard to bathers.
Venom contains a thermolabile toxin.
Fatalities are rare but extensive damage possible.
Symptoms: sharp wound, significant localized pain, hypotension, oculogyric crises, convulsions.
Treatment: avoid incision/suction, carefully cleanse wound, immerse wound in hot water (to destroy toxin), use appropriate painkillers, intensive supportive care as needed.

Jellyfish

Main symptom is local pain, which could be more severe and generalised.
Other symptoms include pain, generalised muscle pains, colic, nausea, breathlessness with cyanosis, may occur rapidly in minutes or be delayed.
Treatment for jellyfish stings: remove any tentacles, use painkillers, local anaesthetic cream. and supportive care.