Comparative titration of three antivenin serums used against sub-Saharan African snakes

The standardisation of serotherapy is necessary in Africa mainly because of the frequency of envenomations and the lack of alternative treatments. Comparative titrations of FAV-Afrique (Aventis Pasteur), Polyvalent serum (Serum Institute of India = SII) and Polyvalent antivenin (South African Vaccine Fabricants Ltd = SAIMR) were carried out on venoms of Echis ocellatus from Cameroun, E. ocellatus from Mali, E. leucogaster and Naja melanoleuca. The 50% protective doses (ED50) of the antivenoms were given according either to i) the in vitro method which consists of inoculating 5 batches of 5 mice with a mixture containing 3 DL50 of venom and increasing volumes of antivenom incubated for 30 mn at 37 degrees C and ii) the in vivo method which consists of successive administration of venom and then antivenom after a 30 to 60 mn interval. The three antivenoms showed a similar efficacy against all the Echis venoms. Interestingly, the SAIMR proved to be effective against the venom of E. leucogaster and E. ocellatus although no venom of Echis was used to immunise horses during the preparation of antivenom. Conversely, this paraspecificity did not exist with the Naja melanoleuca venom against which FAV Afrique showed a higher efficacy. The electrophoresis pattern of FAV-Afrique performed on acetate gel strips showed only one protein fraction (76 g.l-1), whereas both the SII and SAIMR antivenoms showed four fractions whose protein concentrations was respectively 64 g.l-1 and 145 g.l-1.