PRODUCTION AND ASSESSMENT OF OVINE ANTIVENOMS FOR THE TREATMENT OF SNAKE ENVENOMING IN SAUDI ARABIA

Abstract

Venoms from the most poisonous snakes found in Saudi Arabia were assessed for their physical and chemical characteristics and for their enzymatic and biological activities. Venom from Atractaspis microlepidota was the most lethal in mice followed by the elapids Naja haje arabica and Walterinnesia aegyptia. Among the vipers, Cerastes cerastes venom was the most lethal whereas the remainder (Echis pyramidum, Echis coloratus and Bitfis arietans) showed similar but lower lethality. Antivenoms were raised in sheep by immunising with a low dose of venom (0.5mg) which was then doubled every four weeks. To optimise the antibody response, groups of sheep were immunised with a low, medium and high dose and the monthly bleeds were assessed by ELISA and small-scale affinity chromatography. The immunoglobulin fraction was partially purified by sodium sulphate precipitation and digested with either papain, to form Fab fragments, or with pepsin to produce F(ab)2. The different antivenom fractions produced were characterised and assessed for their ability to neutralise the enzymatic and biological activities of the corresponding venoms. Fab was equally effective as F(ab)2 in most enzymatic and biological assays but the two fractions were less efficient than IgG. The ovine Fab provided good protection in mice against the lethality of these venoms and effectively neutralised their biological and enzymatic activities. The commercial antivenoms currently available in Saudi Arabia showed only partial neutralisation of the enzymatic and biological activities of these venoms and showed in vivo protection only when using large amounts. They offered no protection against W. aegyptia venom. The monospecific ovine Fab raised against E. pyramidum and E. coloratus venoms were more efficient than the polyspecific Fab raised against a mixture of the two venoms.