Toxoiding of snake venom and evaluation of immunogenicity of the toxoids.

The venom of Pakistan species of snakes (Naja naja, Vipera russelli and Echis carinatus) and lethal fractions of Cobra (Naja naja) venom were converted to toxoid with formalin. Detoxification of the crude venoms and toxic fraction was attained by addition of formalin in several steps and incubation at 37°C maintaining the pH 7.0. Relationship of formalin concentration and incubation period was studied. The detoxified product retained immunogenicity as revealed by titrating the circulating antitoxin and response of the animals immunized with the crude venom toxoids when challenged with homologous venoms. Vipera russelli and Echis carinatus anti sera neutralized 10 and 15 M.H.D. respectively and on challenging immunized animals with homologous venoms of Naja naja, vipera russelli and Echis carinatus survived 5-10 MLD of the respective venoms. The lethal fraction toxoid of cobra showed lesser immunogenicity (JPMA 30: 9, 1980).