The variation of venom composition with geography is an important aspect of intraspecific variability in the Vipera genus, although causes of this variability remain unclear. The diversity of snake venom is important both for our understanding of venomous snake evolution and for the preparation of relevant antivenoms to treat envenomations. A geographic intraspecific variation in snake venom composition was recently reported for Vipera aspis aspis venom in France. Since 1992, cases of human envenomation after Vipera aspis aspis bites in south-east France involving unexpected neurological signs were regularly reported. The presence of genes encoding PLA₂ neurotoxins in the Vaa snake genome led us to investigate any neurological symptom associated with snake bites in other regions of France and in neighboring countries. In parallel, we used several approaches to characterize the venom PLA₂composition of the snakes captured in the same areas. Buy Vipera aspis Venom Online

Methodology/Principal Findings

We conducted an epidemiological survey of snake bites in various regions of France. In parallel, we carried out the analysis of the genes and the transcripts encoding venom PLA₂s. We used SELDI technology to study the diversity of PLA₂ in various venom samples. Neurological signs (mainly cranial nerve disturbances) were reported after snake bites in three regions of France: Languedoc-Roussillon, Midi-Pyrénées and Provence-Alpes-Côte d’Azur. Genomes of Vipera aspis snakes from south-east France were shown to contain ammodytoxin isoforms never described in the genome of Vipera aspis from other French regions. Surprisingly, transcripts encoding venom neurotoxic PLA₂s were found in snakes of Massif Central region. Accordingly, SELDI analysis of PLA₂ venom composition confirmed the existence of population of neurotoxic Vipera aspis snakes in the west part of the Massif Central mountains.

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Conclusions/SignificanceThe association of epidemiological studies to genetic, biochemical and immunochemical analyses of snake venoms allowed a good evaluation of the potential neurotoxicity of snake bites. A correlation was found between the expression of neurological symptoms in humans and the intensity of the cross-reaction of venoms with anti-ammodytoxin antibodies, which is correlated with the level of neurotoxin (vaspin and/or ammodytoxin) expression in the venom. The origin of the two recently identified neurotoxic snake populations is discussed according to venom PLA₂ genome and transcriptome data.

Four species of vipers of the Vipera genus live in mainland France. Two of these species have not been implicated in causing serious envenomation. Indeed the Basque viper (Vipera seoanei) and the meadow viper (Vipera ursini) are small snakes that live within a restricted area and are not medically significant. The other two French viper species, i.e., the adder (Vipera berus) and the asp viper (Vipera aspis) are larger snakes, ranging from 40 to 60 cm in length, and can cause life-threatening envenomation. Since it is adapted to cold regions, Vipera berus can be found in Scandinavian countries beyond the Arctic polar circle. The northern half of France and the mountainous regions of central France mark the southernmost extension of the habitat of this species. This snake is common in Sweden and England. Vipera aspis, that requires sun and warm temperatures, is found mainly in the regions south of the Loire. It can proliferate in suitable environments. Pattern markings are highly variable, even within the same population. Our reporting of the data concerning Vipera aspis bites in Southeastern France over a 13-year period should provide clinicians with useful insights for the management of patients envenomed by native Vipera species, including those involving neurological toxicity.