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 PLA2 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 LD50 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.

Ontogenetic changes in the venom of Metlapilcoatlus nummifer, the mexican jumping viper.

The viperid genus Metlapilcoatlus (previously Atropoides) is represented in Mexico by four species: M. olmec, M. mexicanus, M. occidus, and M. nummifer. To date, no studies on their venoms have been reported. Here, we comparatively characterized the venom from M. nummifer neonates (≤8 months of age), young adults (18 months) and adults (≥24 months). We performed biological and enzymatic activities, as well as electrophoretic and RP-HPLC profiling combined with proteomic assignment of major fractions. Venoms from neonates and adults differed in their electrophoretic and chromatographic profiles, indicating that an ontogenetic compositional shift occurs in this species. Protein family assignments showed that neonates produce a venom rich in Snake Venom Metalloproteinases (SVMPs) and Snake Venom Serine Proteases (SVSPs), but lacking Phospholipases A2 (PLA2s). In contrast, adults express abundant venom PLA2s, and lower molecular weight proteins, as evidenced by SDS-PAGE. Functionally, neonate venom did not display PLA2 or procoagulant activities, whereas adult venom did. Hemorrhagic activity was present in both neonate and adult venoms, with similar potencies. Finally, it is of considerable concern that the lethal activity of neither neonate nor adult venoms was neutralized by two therapeutic antivenoms produced in Mexico.