African cobras that cause local signs of envenoming and eye lesions (spitting cobras)

Studies

South Africa (Natal)
Tilbury 1982: 6 N. mossambica bites; identification: morphological. A total of 17 cases are described in this study, and in 11 cases it was only possible to identify which snake caused the bite through indirect means (questioning the patient, showing the patient pictures, inference from the clinical symptoms).

Case reports

Zimbabwe
Blaylock 1982a (2 cases).
Strover 1973 (2 cases).

Signs & symptoms

Local effects

Swelling 5/6; 1/6 developed only local pain and no further symptoms, he received antivenom within 25 min after the bite. Necrosis 3/6 (Tilbury 1982).

Development of local effects: within the first 3 h after the bite, moderate to severe local pain and progressive local swelling. 3–5 h after the bite the first signs of the necrotising process are already noticeable (dark discolouration of the skin, formation of blisters, discharge of blood-tinged serous fluid). 5–9 h after the bite the skin discolouration is more extensive, and it reaches a maximum after 9–48 h. The affected area of skin is now dark blue and demarcated. 48–72 h after the bite the swelling reaches a maximum, the skin discolouration becomes black, and blisters appear over the entire area of skin discolouration. The swelling starts to reduce from day 3. During surgical exploration or debridement it can be seen that even subcutaneous tissue under epidermis that is not discoloured and destroyed has become necrotic. Pockets of necrotic tissue that extend far beyond the demarcated area can be found. After debridement, an ulcer forms with an undermined edge. In the observed cases, generally only the epidermis and subcutaneous tissue were affected, and not the musculature or other deep tissue structures (Tilbury 1982).

Loss of fluid into the sometimes massive swelling of the bitten extremity. In children in particular this is a factor that can contribute to hypovolaemia and hypovolaemic shock (Tilbury 1982).

Accidents in which venom is sprayed into the eye: 4½ h after the accident: bilateral blepharospasm, severe conjunctivitis, dilated pupil with slow reaction to light. After 24 h the pupils were the same size and both reacted the same to light (Tilbury 1982).

Other signs & symptoms

Drowsiness (probably a non-specific symptom related to dehydration, exhaustion).

Case fatality rate

0/6 (Tilbury 1982).

Morbidity

Necroses that may be extensive and can lead to loss of soft tissue, loss of function and loss of limbs. Exacerbation due to secondary effects (wound infection).

Accidents in which venom is sprayed into the eye: conjunctivitis, corneal ulceration, blindness if the injury is not treated.

Treatment (symptomatic)

1. Antibiotic treatment in patients who had made an incision to treat the bite and who developed necroses (penicillin and gentamicin) (Tilbury 1982).

2. Surgical debridement and split-thickness skin grafting (Tilbury 1982).

Treatment (specific)

No controlled clinical studies available. Data regarding the efficacy of antivenom in the study of Tilbury 1982.

Antivenom

Polyvalent antivenom (SAIMR, Johannesburg).

Indications for administration of antivenom
No uniform indications given in the study of Tilbury 1982. 5/6 patients received antivenom.

Dose
55–100 ml (Tilbury 1982).

Efficacy

With regard to local cytotoxicity and the development of necroses: 2 patients with moderately severe to severe local/regional swelling presented at the hospital 3.5 and 5.5 h after the bite and received 100 and 55 ml, respectively, of SAIMR antivenom. Both patients developed extensive necroses. 2 patients were hospitalised 3 and 1.5 h after the bite, with mild swelling. Each received 100 ml of SAIMR antivenom; 1 developed a small abscess while the other had no skin or soft tissue defects. 1 patient was hospitalised after 25 min, had no swelling, received 80 ml of SAIMR antivenom and showed no further consequences of the envenoming (Tilbury 1982).

Evaluation and recommendations

The available data do not allow a clear conclusion to be made regarding the efficacy of the antivenom. In terms of local effects, the efficacy appears to diminish rapidly the longer the time between the bite and administration of antivenom (Tilbury 1982).