Immunogenicity of a toxoid of Habu (Trimeresurus flavoviridis) venom in various animal species including man.

A mixed toxoid consisting of HR1 and HR2 toxoids derived from Habu (Trimeresurus flavoviridis) venom was examined for immunogenicity in guinea pigs, rabbits, monkeys and human beings. The toxoid produced both anti-HR1 and anti-HR2 in various animals. The immunogenicity of the toxoid was superior to a crude toxoid in both guinea pigs and monkeys. Immunized monkeys showing circulating antitoxin potencies of more than 10-20 units per ml for both anti-HR1 and anti-HR2 tolerated the challenge with crude Habu venom of 5-10mg, which is very close to the amount of the venom ejected by a single snake bite. The evidence may suggest that the toxoid contained all the antigens essential for protection from Habu snake bites. Human volunteers produced anti-HR1 and anti-HR2 to 2-4 units/ml and 7-11 units/ml, respectively after 3 injections of the mixed toxoid. Although the toxoid may serve as useful prophylactic for Habu bite, no explanation can be given to the following findings: (1) In guinea pigs and rabbits, the ratios of the potency of anti-HR1 to that of anti-HR2 were similar and the former was higher than the latter. In monkeys and humans, the relation was the reverse. (2) The immunized monkeys resisted a larger dose of crude venom than the guinea pigs, although the antitoxin titers were similar and the lethal doses of the venom to both species are almost the same. (3) Unlike other kinds of toxoid, response of the immunized animals to the booster injection was rather poor, especially in human beings.