[Exotic snakes in Europe. A case of Mexican Moccasin (Agkistrodon bilineatus) snakebite]

Blood Lines: Intraspecific and Interspecific Variations in Anticoagulant Actions of Agkistrodon Viperid Venoms

This study investigated the intraspecific and interspecific variability in the venom effects of Agkistrodon viperid snake species and subspecies (eleven venoms total) on plasma clotting times, fibrinogen levels, and fibrin clot strength. Significant delays in plasma clotting time were observed for A. conanti, A. contortrix mokasen, A. contortrix phaeogaster, A. howardgloydi, A. piscivorus leucostoma, and A. piscivorus piscivorus. Notably, the phylogenetically disjunct lineages A. conanti, A. contortrix mokasen, and A. howardgloydi exhibited the most potent anticoagulant effects, indicating the independent amplification of a basal trait. Inhibition assays with the activated clotting enzymes Factors XIa, IXa, Xa, and IIa (thrombin) revealed that FXa inhibition is another basal trait amplified independently on multiple occasions within the genus, but with A. howardgloydi, notably more potent than all others. Phospholipid degradation and zymogen destruction were identified as mechanisms underlying the variability in venom effects observed experimentally and in previous clinical reports. Thromboelastography demonstrated that the venoms did not clot fibrinogen directly but affected fibrin clot strength by damaging fibrinogen and that thrombin was subsequently only able to cleave into weak, unstable clots. The ability to activate Protein C, an endogenous anticoagulant enzyme, varied across species, with some venoms exceeding that of A. contortrix contortrix, which previously yielded the protein diagnostic agent Protac®. Phylogenetic analysis suggested that both fibrinogen degradation and Protein C activation were each amplified multiple times within the genus, albeit with negative correlation between these two modes of action. This study highlights the evolutionary, clinical, and biodiscovery implications of venom variability in the Agkistrodon species, underscoring their dynamic evolution, emphasising the need for tailored clinical approaches, and highlighting the potential for novel diagnostic and therapeutic developments inspired by the unique properties of snake venoms.

Snakebite Envenoming Diagnosis and Diagnostics

Snakebite envenoming is predominantly an occupational disease of the rural tropics, causing death or permanent disability to hundreds of thousands of victims annually. The diagnosis of snakebite envenoming is commonly based on a combination of patient history and a syndromic approach. However, the availability of auxiliary diagnostic tests at the disposal of the clinicians vary from country to country, and the level of experience within snakebite diagnosis and intervention may be quite different for clinicians from different hospitals. As such, achieving timely diagnosis, and thus treatment, is a challenge faced by treating personnel around the globe. For years, much effort has gone into developing novel diagnostics to support diagnosis of snakebite victims, especially in rural areas of the tropics. Gaining access to affordable and rapid diagnostics could potentially facilitate more favorable patient outcomes due to early and appropriate treatment. This review aims to highlight regional differences in epidemiology and clinical snakebite management on a global scale, including an overview of the past and ongoing research efforts within snakebite diagnostics. Finally, the review is rounded off with a discussion on design considerations and potential benefits of novel snakebite diagnostics.

Commissioned article: management of exotic snakebites

Exotic (foreign or non-native) snakes, including venomous species, are becoming increasingly popular pets in Western countries. Some of them are kept illegally (as defined by the UK Dangerous Wild Animals Act of 1976). There is a large international market for such animals, with contraventions of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). In the UK, several other European countries and the USA the reported numbers of bites by venomous exotic snakes, although small, are increasing but still underestimate the occurrence of these occasionally fatal events because of the victims' reluctance to seek medical care. Victims are predominantly young men who have been drinking alcohol. Bites may be intentionally provoked. In Europe, the species most often involved are cobras, green mambas, American pit vipers particularly rattlesnakes, African adders, vipers and Asian green pit vipers. To illustrate the special problems involved, case histories are presented of bites by exotic species in the UK and of bites abroad, where patients were repatriated for treatment. In view of the relative rarity and diversity of these cases, expert advice must usually be sought. These requests should include information about the species thought to have been responsible and the history and timing of the evolution of envenoming. Sources of advice and antivenom are discussed together with recommendations for appropriate first aid and emergency treatment while this is being awaited. Respiratory and cardiovascular resuscitation may be required and when systemic or severe local envenoming develops, specific (equine or ovine) antivenom is indicated.