Polyspecific snake antivenom may help in antivenom crisis

Editor—In Africa snakebites cause thousands of deaths annually and much permanent physical disability, but the supply of antivenom, the only specific treatment, is threatened by commercial pressures and privatisation. This has been caused over the past few years by the cessation of antivenom manufacture by Behringwerke in Germany, greatly reduced production by Aventis Pasteur in France, and the threat to continued production by Africa's sole remaining producer, the African Health Laboratory Service in Johannesburg.

Without antivenom, human suffering and death from snake bite are increasing, especially in west Africa.¹ Only conservative treatment is possible, or the use of ineffective antivenoms manufactured in Asia or dangerous traditional remedies.

In February 2001 a workshop held by the World Health Organization identified interregional collaboration as the only short term solution.² Colombia's national institute for public health responded by offering to develop a prototype pan-African polyspecific antivenom.

Venoms from nine species of Echis, Bitis, and Naja were selected as being medically the most important in Africa (a mamba antivenom is being developed separately). Horses were hyperimmunised with 13 African venoms using the Colombian institute's standard protocol. The neutralising potency of the equine antiserum in WHO standard preclinical assays against five intravenous median lethal doses of the individual and pooled venoms was sufficiently high to justify the purification of the crude antiserum to produce a definitive antivenom.³

In preclinical tests this antivenom showed good neutralising potency against the venoms covered by the African Health Laboratory Service's polyspecific antivenom. The new antivenom also neutralised the venoms of saw scaled vipers (genus Echis) (ED₅₀ 14.3 μl/mouse) as effectively as both the African Health Laboratory Service's Echis antivenom (12.8 μl/mouse) and Micropharm's Echis ocellatus Fab fragment antivenom (13.0 μl/mouse.⁴ Unlike these two monospecific antivenoms, the pan-African antivenom powerfully neutralises the venom of Bitis arietans (1.3 μl/mouse) and has moderate activity against Naja nigricollis venom (73.0 μl/mouse). These species cause most serious snakebites in Africa.

Another polyspecific African antivenom (developed in Costa Rica) and a new Micropharm monospecific E ocellatus F(ab′)₂ fragment antivenom are undergoing preclinical testing. These three antivenoms will be compared by randomised controlled trials in Nigeria.