Snake venom variability: methods of study, results and interpretation.

The causes and implications of venom variability are discussed with a review of the literature. Venom variability may have an impact on both primary venom research and management of snakebite, including selection of antivenoms and selection of specimens for antivenom production. Choice of venom is reviewed, including venom collection, maintenance, and pooled venom versus venom milked from individual specimens, the latter being more reliable in many applications. Intraspecific variability resulting in clinical variability of envenomation occurs and is reviewed. Venom variability is considered at several levels; interfamily, intergenus, interspecies, intersubspecies and intraspecies, geographical variation, between individual specimens, and in individual specimens, due to seasonal variation, diet, habitat, age-dependent change, and sexual dimorphism. It is concluded that venom researchers must be aware of venom variability both in selecting their sources of venom and in interpretation of results. Producers of antivenom must utilize an understanding of such variability in selecting sources of venom for antivenom production to ensure representation of all venom types required within each antivenom. Furthermore, clinicians treating snakebite should understand the influence of venom variability on both the presentation of envenomation and the treatment implications.