Abstract
The snake genus Daboia (Viperidae: Viperinae; Oppel, 1811) contains five species: D. deserti, D. mauritanica, and D. palaestinae, found in Afro-Arabia, and the Russell’s vipers D. russelii and D. siamensis, found in Asia. Russell’s vipers are responsible for a major proportion of the medically important snakebites that occur in the regions they inhabit, and their venoms are notorious for their coagulopathic effects. While widely documented, the extent of venom variation within the Russell’s vipers is poorly characterised, as is the venom activity of other species within the genus. In this study we investigated variation in the haemotoxic activity of Daboia using twelve venoms from all five species, including multiple variants of D. russelii, D. siamensis, and D. palaestinae. We tested the venoms on human plasma using thromboelastography, dose-response coagulometry analyses, and calibrated automated thrombography, and on human fibrinogen by thromboelastography and fibrinogen gels. We assessed activation of blood factors X and prothrombin by the venoms using fluorometry. Variation in venom activity was evident in all experiments. The Asian species D. russelii and D. siamensis and the African species D. mauritanica possessed procoagulant venom, while D. deserti and D. palaestinae were net-anticoagulant. Of the Russell’s vipers, the venom of D. siamensis from Myanmar was most toxic and D. russelli of Sri Lanka the least. Activation of both factor X and prothrombin was evident by all venoms, though at differential levels. Fibrinogenolytic activity varied extensively throughout the genus and followed no phylogenetic trends. This venom variability underpins one of the many challenges facing treatment of Daboia snakebite envenoming. Comprehensive analyses of available antivenoms in neutralising these variable venom activities are therefore of utmost importance.
Highlights
The animal kingdom possesses a stunning diversity of venomous animals, with almost every major lineage containing a multitude of venomous species [1]
Of the Afro-Arabian clade, only D. mauritanica possessed procoagulant venom, while D. deserti and D. palaestinae venoms induced an anticoagulant effect in plasma
Both anticoagulant and procoagulant venom properties were mutually evident within most venoms, as all but D. siamensis from Myanmar demonstrated anticoagulant fibrinogenolysis, though by widely differing mechanisms, and all acted upon factor X and prothrombin in a procoagulant manner
Summary
The animal kingdom possesses a stunning diversity of venomous animals, with almost every major lineage containing a multitude of venomous species [1]. Their notoriety stems from the susceptibility of humans to their venoms, which snakes may deploy when under perceived threat. Many toxins target molecules that are conserved within and between major animal groups, such as neuroreceptors or blood proteins [3,4]. Their activity is often effective in the bodies of a broad range of animals. This partly explains the vulnerability of human physiology to many snake species’ venoms, those that are adapted to feeding on mammals
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