Intraspecific venom variation of Mexican West Coast Rattlesnakes (Crotalus basiliscus) and its implications for antivenom production.

Intraspecific variation in snake venoms has been widely documented worldwide. However, there are few studies on this subject in Mexico. Venom characterization studies provide important data used to predict clinical syndromes, to evaluate the efficacy of antivenoms and, in some cases, to improve immunogenic mixtures in the production of antivenoms. In the present work, we evaluated the intraspecific venom variation of Crotalus basiliscus , a rattlesnake of medical importance and whose venom is used in the immunization of horses to produce one of the Mexican antivenoms. Our results demonstrate that there is variation in biological and biochemical activities among adult venoms and that there is an ontogenetic change from juvenile to adult venoms. Juvenile venoms were more lethal and had higher percentages of crotamine and crotoxin, while adult venoms had higher percentages of snake venom metalloproteases (SVMPs). Additionally, we documented crotoxin-like PLA 2 variation in which specimens from Zacatecas, Sinaloa and Michoacán (except 1) lacked the neurotoxin, while the rest of the venoms had it. Finally, we evaluated the efficacy of three lots of Birmex antivenom and all three were able to neutralize the lethality of four representative venoms but were not able to neutralize crotamine. We also observed significant differences in the LD 50 values neutralized per vial among the different lots. Based on these results, we recommend including venoms containing crotamine in the production of antivenom for a better immunogenic mixture and to improve the homogeneity of lots. [Display omitted] • The venom of Crotalus basiliscus showed ontogenetic variation. • Crotamine was present in significant proportions in juvenile venom. • Crotoxin polymorphism was found in the venom of Crotalus basiliscus. • Mexican antivenom batches showed variations in neutralization. • The antivenom was not able to neutralize crotamine. Key Contribution: We identified ontogenetic and geographic venom variation within Crotalus basiliscus based on enzymatic and biological activities and we describe polymorphism for crotoxin-like PLA 2 s. Venom neutralization efficacy of Birmex antivenom, for which C. basiliscus is an immunogen, varies among lots. [ABSTRACT FROM AUTHOR]