Venom and antivenom

The fauna of Saudi Arabia comprises a large number of venomous species of snakes, fish, scorpions, insects, coelenterates and molluses. The venoms of these animals show a remarkable diversity of actions on human tissues. Neurotoxins (for example, from the Arabian cobra Naja haje arabica) interrupt transmission at peripheral neuromuscular junctions or (for example scorpion neurotoxins) stimulate voltage sensitive synaptic sodium and potassium channels with release of acetylcholine and catecholamines. The venoms of Red Sea carnivorous marine snails (genus Conus) contain 'conotoxins' which have effects on voltage sensitive calcium and sodium channels, acetylcholine receptors, the vasopressin receptor and N-methyl-D-aspartate receptors. Of particular interest are sarafotoxins from the venom of the burrowing asp (Atractaspis engaddensis, Atractaspididae), which cause coronary artery vasoconstriction and atrioventricular block. They are homologous with human endogenous endothelins. Human victims of bites by this species may die very rapidly after developing anaphylactic/autonomic symptoms, shock and atrioventricular conduction abnormalities. Improved ovine Fab fragment antivenoms are being developed for treatment of envenoming by Saudi Arabian snakes and scorpions. These Fab antivenoms have the pharmacological advantage of more rapid tissue distribution, a larger apparent volume of distribution and less risk of Fc or aggregate-induced complement activation than conventional F (ab1)2 antivenoms.