Spider Envenomation
Description General measures Medicine treatment T63.3 + (X21.99) DESCRIPTION Local venomous spiders are divided into cytotoxic and neurotoxic groups. To view pictures for the identification of spiders: http://www.cmej.org.za/index.php/cmej/article/view/2547/2582 Cytotoxic spider group The cytotoxic group includes sac, violin, and crab spiders. Lesions may present with significant bite site necros
T63.3 + (X21.99)
DESCRIPTION
Local venomous spiders are divided into cytotoxic and neurotoxic groups. To view pictures for the identification of spiders:
http://www.cmej.org.za/index.php/cmej/article/view/2547/2582
Cytotoxic spider group
The cytotoxic group includes sac, violin, and crab spiders. Lesions may present with significant bite site necrosis, for which surgical debridement may be required. Bites can take weeks/months to heal.
Note:
Antibiotics are reserved for secondary infection.
Neurotoxic spider group
The neurotoxic group is represented by the button spider (also known as widow spiders), genus Latrodectus. Black button spiders are more venomous than brown button spiders.
Features useful in the identification of the black button spider are:
- Black or dark brown colour.
- Variable red markings on the dorsal aspect of the abdomen, which diminish with age. It has no ventral markings.
Features of brown button spider:
- Light brown to creamy yellow to pitch black in colour.
- Typical red-orange hourglass-shaped marking on the ventral surface of the abdomen.
Envenomation from black button spiders may cause:
- Immediate local burning pain and tender regional lymph nodes within an hour.
- Severe general muscle pain, cramps, and rigidity especially of the large girdle muscles
- Causes feeling of tightness of the chest and board-like rigidity of a non-tender abdomen.
- Lasts for days to a week if antivenom is not given.
- Profuse sweating may be prominent.
- Diffuse paraesthesia, especially of the hands and feet.
GENERAL MEASURES
Observe all cases of potential neurotoxic spider bite for at least 24 hours.
MEDICINE TREATMENT
- Spider antivenom is only indicated for systemic symptoms of neurotoxicity in patients with button spider bites.
- Antivenom available from South African Vaccine Producers: (refer to the Envenomation table for contact details). See full details in the package insert.
- Spider antivenom, IV infusion, 5–10 mL diluted in 50–100 mL sodium chloride, 0.9% or dextrose 5%, administered over 5–10 minutes.
LoE:IVbxvii
CAUTION
Never administer antivenom without being prepared to manage acute anaphylaxis.
Immunisation, primary or booster:
(Z23.5)
- Tetanus toxoid vaccine, IM, 0.5 mL immediately, if not previously immunised within the last 5 years.
In unimmunised or partially immunised patients:
(Z23.5)
- Tetanus immunoglobulin, human, IM, 250 units immediately.
Analgesia
For mild pain:
- Paracetamol, oral, 500mg to 1 g 4–6 hourly when required (to a maximum of 4 g in 24 hours)
- Maximum dose: 15 mg/kg/dose.
Severe muscle pain and cramps:
- Calcium gluconate 10%, bolus IV infusion, 10 mL over 10 minutes.
- Repeat if needed, only once, i.e. maximum recommended dose of 2 grams.
Note:
Effect may only last for 20–30 minutes and there is a limited amount that can be given.
LoE:IVbxviii
For secondary infection:
Standard Treatment Guidelines and Essential Medicines List for South Africa, Adult Hospital Level, 2020-2024_Version 2.0_27 March 2025
Chapter 19 Poisoning_19.4 Spider Envenomation