Production and assessment of ovine antivenoms for the treatment of envenoming in Saudi Arabia.
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.