Development of an ELISA to assess the potency of horse therapeutic antivenom against Thai cobra venom.

An ELISA for the quantitation of antibodies against Naja naja siamensis venom proteins has been developed for use as a possible replacement for the in vivo neutralization assay of antivenom potency. Comparison was made with three preparations of venom proteins as antigens of ELISA: these were the crude venom, a toxin fraction and the purified principle postsynaptic neurotoxin of the Thai cobra. Eight batches of horse monovalent therapeutic anti-cobra antivenom, one of which served as positive reference, were assayed by the ELISAs and also by the in vivo neutralization assay using mice. When crude venom, the toxin fraction and the pure neurotoxin were used as antigens in the ELISAs, the correlation coefficients between the ELISA antibody titers and in vivo neutralization of the antivenoms were 0.82 (P less than 0.005), 0.94 (P less than 0.001) and 0.95 (P less than 0.001), respectively. Thus, the ELISA which measures only the antibody against the principle toxin of the snake venom should be most suitable for use as an in vitro assay of antivenom potency. The ELISA should also be useful for potency assessment and standardization of antivenoms against other elapid snake venoms whose lethal components are small, poorly immunogenic peptides.