Venomics of Bungarus caeruleus (Indian krait): Comparable venom profiles, variable immunoreactivities among specimens from Sri Lanka, India and Pakistan

Abstract

The Indian krait (Bungarus caeruleus) is one of the "Big Four" venomous snakes widely distributed in South Asia. The present venomic study reveals that its venom (Sri Lankan origin) is predominated by phospholipases A₂ (64.5% of total proteins), in which at least 4.6% are presynaptically-acting β-bungarotoxin A-chains. Three-finger toxins (19.0%) are the second most abundant, comprising 15.6% κ-neurotoxins, the potent postsynaptically-acting long neurotoxins. Comparative chromatography showed that venom samples from Sri Lanka, India and Pakistan did not exhibit significant variation. These venoms exhibited high immunoreactivity toward VINS Indian Polyvalent Antivenom (VPAV). The Pakistani krait venom, however, had a relatively lower degree of binding, consistent with its moderate neutralization by VPAV (potency=0.3mg venom neutralized per ml antivenom) while the Sri Lankan and Indian venoms were more effectively neutralized (potency of 0.44 mg/ml and 0.48 mg/ml, respectively). Importantly, VPAV was able to neutralize the Sri Lankan and Indian venoms to a comparable extent, supporting its use in Sri Lanka especially in the current situation where Sri Lanka-specific antivenom is unavailable against this species. The findings also indicate that the Pakistani B. caeruleus venom is immunologically less comparable and should be incorporated in the production of a pan-regional, polyspecific antivenom.

Biological significance: The Indian krait or blue krait, Bungarus caeruleus, is a highly venomous snake that contributes to the snakebite envenoming problem in South Asia. This is a less aggressive snake species but its accidental bite can cause rapid and severe neurotoxicity, in which the patient may succumb to paralysis, respiratory failure and death within a short frame of time. The proteomic analysis of its venom (sourced from Sri Lanka) unveils its content that well correlates to its envenoming pathophysiology, driven primarily by the abundant presynaptic and postsynaptic neurotoxins (β-bungarotoxins and κ-neurotoxins, respectively). The absence of cytotoxins in the venom proteome also correlates with the lack of local envenoming sign (pain, swelling), and explains why the bite may be insidious until later stage when paralysis sets in. The muscarinic toxin-like proteins in the venom may be the cause of severe abdominal pain that precedes paralysis in many cases, and justifies the need of closely monitoring this symptom in suspected cases. Venom samples from Sri Lanka, India and Pakistan exhibited no remarkable variation in protein profiling and reacted immunologically toward the VINS Indian Polyvalent Antivenom, though to a varying extent. The antivenom is effective in neutralizing the Sri Lankan and Indian venoms, confirming its clinical use in the countries. The antivenom efficacy against the Pakistani venom, however, may be further optimized by incorporating the Pakistani venom in the antivenom production.

Keywords: Antivenom neutralization; Bungarus caeruleus; Indian krait; Venomics.