Geographical and intraspecies variation in the clinical manifestations of envenoming by snakes

Abstract The range and severity of clinical manifestations after a bite by a particular species of snake and hence the prognosis depend on the quantity of venom injected, its composition, the site and depth of the bite, the age and previous health of the victim and the quality of first aid and medical treatment. The quantity and composition of venom will vary with the age/size of the snake, the mechanical efficiency of the bite and the amount of venom present in the venom apparatus immediately before the strike. Variation in venom composition and antigeniciity throughout the geographical range of a single ‘species ‘ has been documented and, even at a particular geographical locus, composition of venom from individual snakes of the same age/size may not be homogeneous. All these sources of variation make it difficult to predict the outcome of a bite and to provide guidelines for clinical management, even if the species is known. Optimal medical treatment depends on the precise identification of the biting species. Ideally, this will be based on examination of the snake responsible for the bite or on rapid identification of specific venom antigen in the patient ‘s serum or other body fluids, for example by enzyme immunoassay. Failing that, the clinician must decide on the most likely species, based on the circumstances of the bite, the patient ‘s description of the appearance and behaviour of the snake and the symptoms and signs of envenoming. For antivenom production, use of a pool of venom from correctly identified snakes of different ages/sizes and geographical origins is essential in view of the intraspeciies variation in venom composition and antigenicity.