Abstract:
African spitting cobra, Naja nigricincta nigricincta (Zebra snake), envenomation is an important cause of snakebite
morbidity and mortality in Namibia. The snake is endemic to central and northern Namibia as well as southern
Angola. The venom is mainly cytotoxic, resulting in aggressive dermo-necrosis and often accompanied by severe
systemic complications. No specific antivenom exists. Rhabdomyolysis, systemic inflammatory response, haemostatic
abnormalities, infective necrotising fasciitis as well as acute kidney failure have been documented.
Based on murine models, this study assessed SAVP/SAIMR - and EchiTAb-Plus-ICP polyvalent antivenom
neutralisation as well as subdermal necrosis. Additional muscle, cardiac, kidney and lung histology, creatine
kinase measurements and post-mortems were performed.
An intravenous median lethal dose (LD50) of Naja nigricincta nigricincta venom was determined at 18.4 (CI:
16.3; 20.52) μg and a subdermal lethal dose at 15.3(CI: 12.96; 17.74)μg. The SAIMR/SAVP polyvalent antivenom
median effective dose (ED50) was 1.2 ml antivenom/1 mg venom equating to a potency (WHO) of 1 ml antivenom
neutralising 0.63 mg venom and approximately 240 ml (24 vials) needed for initial treatment. The ED50
of the EchiTAb-Plus-ICP was 1 ml antivenom/1 mg venom and a potency of 65 mg venom/ml antivenom (3.3 x
LD50), estimating 230 ml (23 vials) for treatment.
Histology and serology (creatine kinase) evidenced venom induced skeletal myotoxicity, which was not
prevented by the antivenoms tested. Cardiac myonecrosis, an inflammatory response, direct venom kidney
tubular necrosis and cardio-pulmonary failure were documented.
