Non-front-Fanged Colubroid (“Rear-Fanged”) Snakes

Abstract

Non-front-fanged colubroid snakes (NFFC; formerly and artificially taxonomically assembled as “colubrids”) comprise the majority of extant ophidian species. Although the medical risks of bites by a handful of species have been documented, the majority of these snakes have oral products (Duvernoy’s secretions, or venoms) with unknown biomedical properties and their potential for causing harm in humans is unknown. Several genera of NFFC (the African boomslang, Dispholidus typus; the African twig, bird or vine snakes, Thelotornis spp.; the Japanese tiger keelback or Yamakagashi, Rhabdophis tigrinus; the red-necked keelback, R. subminiatus, and the rare Sri Lankan endemic, the blossom krait, Balanophis ceylonenesis) have inflicted life-threatening or fatal bites (termed, Hazard Level 1), while envenoming by several other NFFC species (e.g. Lichtenstein’s green racer, Philodryas olfersii; the Montpellier snake, Malpolon monspessulanus, and, possibly, the brown tree snake, Boiga irregularis) have caused uncommon systemic envenoming that were not life-threatening (Hazard Level 2). Several other NFFC taxa occasionally inflict bites that cause mild-moderate local envenoming that may resemble that caused by a crotaline viperid species (Hazard Level 2/3). The majority of documented bites from NFFC have either caused only mild local effects with limited medical significance, and bites from some taxa only occasionally cause more locally progressive effects (Hazard Level 3), while most are medically insignificant (Hazard Level 4). However, only a relative handful of bites or envenoming by NFFC taxa have been formally medically reviewed and documented, and thus the medical risks of the majority of NFFC species remain unestablished. Antivenom is available for serious envenoming by D. typus and R. tigrinus; the latter antivenom is probably also effective for treatment of envenoming by R. subminiatus and possibly B. ceylonensis. Medical management of most other species consists of supportive treatment, meticulous wound care and pain management. The controversial use of replacement therapy is discussed, and recommendations are detailed for management of each Hazard Level group. Future qualified documentation of NFFC bites and envenoming may facilitate improved risk assessments of a greater array of NFFC species.