EXPERIMENTAL EVALUATION OF OVINE ANTISERA TO THAI COBRA (NAJA-KAOUTHIA) VENOM AND ITS ALPHA-NEUROTOXIN

Conventional treatment of Naja kaouthia (Thai cobra) envenoming requir es large volumes (up to 600 ml) of equine antivenom, which results in a high incidence of serum reactions. The inefficiency of the antivenom is assumed to be related to the high percentage (approx. 20%) of alph a-neurotoxin, a relatively weak and highly toxic immunogen, present in the native venom. First, antibodies to N. kaouthia venom were raised in sheep, which protected mice against challenge with whole venom. Sec ond, ovine antibodies to the purified neurotoxin and to three differen t neurotoxin conjugates were developed and their neutralising abilitie s against either whole venom or neurotoxin were compared using murine ED(50) tests. High titre antibodies, assessed by enzyme immunoassay an d Western blot, were obtained from all four neurotoxin immunisation re gimens. Neurotoxin conjugated to rabbit anti-sheep Ige produced the hi ghest titres against both neurotoxin and whole venom. This antiserum p rovided protection against neurotoxin challenge but failed to protect against whole venom. Furthermore, the addition of neurotoxin antibodie s to whole venom antiserum did not enhance the neutralisation efficacy of the latter. These findings raise the possibility that in mice othe r toxins apart from the neurotoxin may significantly contribute to the lethal effect of N. kaouthia venom.