Immunogenicity of venoms from four common snakes in the South of Vietnam and development of ELISA kit for venom detection.

The antigenicity and antigenic relationship between venoms of four common snakes in the South of Vietnam-Trimeresurus popeorum, Calloselasma rhodostoma, Naja naja and Ophiophagus hannah-were studied. Most of venom components expressed antigenicity and produced high titre antivenoms. The venoms share common components and antivenoms cross-reacted along them. Furthermore, cross-reactions were observed among non-common antigens, indicating that they share common epitopes. Hence, using single component as immunogen for species diagnosis of snakebites can reduce cross-reaction, perhaps may not be totally specific. A three-step affinity purification protocol was set up for preparation of species-specific antivenom antibodies. The steps involved affinity chromatography of IgG from hyper-immunized rabbit sera with protein A columns, immuno-affinity chromatography of monovalent antivenom antibodies with respective homologous venom columns, and immuno-absorption of cross-species reacting antibody molecules with heterologous venom columns. The antibodies were then used for construction of an enzyme-linked immunosorbent assay (ELISA) test kit. The kit can differentiate among the four common snake venoms in various types of samples with the detection limit of 0.2-1.6 ng/ml, depending on the type of samples and species of the snake. The efficacy of this kit for snake venom detection was successfully demonstrated in experimental envenomation in rats. Preliminary evaluation with 140 samples taken from 88 human snakebite victims in Vietnam showed that the kit could detect venom in human samples and would be a very useful tool for fast identification of snakebites in clinics.