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Toxins affecting blood coagulation

The human haemostatic system seems a favourite target of snake venoms. There are toxins targeting almost all parts of the system, represented in three of the four snake families (Colubridae, Elapidae, Viperidae). The major toxin groups include procoagulants, anticoagulants, platelet aggregation inhibitors and promoters. The net effect of most of these toxins is to increase bleeding, particularly when combined with haemorrhagins, but a few venoms cause clinical thrombosis, with potential for embolic problems. The mechanisms of increased bleeding vary, but most components acting as procoagulants exert their effect by consumption of fibrinogen, resulting in defibrination rather than classic DIC, thus the thrombocytopenia associated with DIC is often absent. However, some venoms do cause thrombocytopenia through other mechanisms. Yet other venoms cause defibrination by direct action on fibrinogen, splitting fibrinopeptides inappropriately. The biochemical nature and structure of these diverse toxins varies from comparatively small molecules to large, complex multi-component toxins that mimic normal clotting complexes such as the prothrombinase complex. The majority of viper species have toxins affecting coagulation, but only a few Elapid species, notably those from Australia and New Guinea, cause similar effects.

Principal types of toxin effects on the haemostatic system.

Toxin type Effect
  1. Factor V activating
  2. Factor X activating
  3. Factor IX activating
  4. Prothrombin activating
  5. Fibrinogen clotting
  1. Protein C activating
  2. Factor IX/X activating protein
  3. Thrombin inhibitor
  4. PLA2
  1. Fibrin(ogen) degradation
  2. Plasminogen activation
Vessel wall interactive
  1. Haemorrhagin
Platelet activity
  1. Platelet aggregation inducers
  2. Platelet aggregation inhibitor
Plasma protein activators
  1. SERPIN inhibitor

Snakes considered to cause medically significant effects on the haemostatic system.

Scientific name Common name Effect
Dyspholidus typus Boomslang Coagulopathy & haemorrhage

Thelotornis spp.
Vine snakes Coagulopathy & haemorrhage
Rhabdophis spp. Yamakagashi, red necked keelback Coagulopathy & haemorrhage
Hoplocephalus spp. Australian broad headed snakes Coagulopathy & haemorrhage
Micropechis ikaheka New Guinea small eyed snake Anticoagulant & haemorrhage
Notechis spp. Australian tiger snakes Coagulopathy & haemorrhage
Oxyuranus spp. Australian taipans Coagulopathy & haemorrhage
Pseudechis spp. Australian mulga snakes Anticoagulant & haemorrhage
Pseudonaja spp.
Australian brown snakes

Coagulopathy & haemorrhage
Tropidechis carinatus Rough scaled snake Coagulopathy & haemorrhage
Agkistrodon spp. American copperheads Coagulopathy & haemorrhage
Bitis spp. African puff adders, Gaboon vipers etc Coagulopathy & haemorrhage
Bothrops spp.
Includes Bothriechis, Cerriphidion, Ophryacus, Porthidium spp.
Central & South American pit vipers Coagulopathy & haemorrhage
Bothrops lanceolatus Martinique viper Coagulopathy; thrombosis with DVT and pulmonary embolus
Calloselasma rhodostoma Malayan pit viper Coagulopathy & haemorrhage
Cerastes spp. North African horned vipers Coagulopathy & haemorrhage
Crotalus spp. (selected) North American rattlesnakes Coagulopathy & haemorrhage
Daboia russelii Russell’s viper Coagulopathy & haemorrhage
Echis spp. Saw scaled vipers Coagulopathy & haemorrhage
Lachesis spp. Bushmasters Coagulopathy & haemorrhage
Trimeresurus spp. Green pit vipers Coagulopathy & haemorrhage

Vipera spp. (selected)
Includes Macrovipera spp.

Selected European vipers Coagulopathy & haemorrhage


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