The recombinant antibody fragments generated against the toxic components of scorpion venoms are considered a promising alternative for obtaining new antivenoms for therapy. Using directed evolution and site-directed mutagenesis, it was possible to generate a human single-chain antibody fragment with a broad cross-reactivity that retained recognition for its original antigen. This variant is the first antibody fragment that neutralizes the effect of an estimated 13 neurotoxins present in the venom of nine species of Mexican scorpions. This single antibody fragment showed the properties of a polyvalent antivenom. These results represent a significant advance in the development of new antivenoms against scorpion stings, since the number of components would be minimized due to their broad cross-neutralization capacity, while at the same time bypassing animal immunization.

Nowadays, the trends in the research devoted to develop novel antidotes against scorpion stings have showed excellent results with the use of recombinant antibody fragments. The polyclonal character of commercial anti-venoms, obtained through the immunization of animals and which contain several neutralizing antibodies that recognize different epitopes on the toxins, guarantees the neutralization of the venoms. To avoid the use of animals we aimed to develop an equivalent recombinant anti-venom composed of a few neutralizing single chain antibody fragments (scFvs) that bind to two different epitopes on the scorpion toxins. In this study, we obtained scFv RU1 derived from scFv C1. RU1 showed a good capacity to neutralize the Cn2 toxin and whole venom of the scorpionCentruroides noxius. Previously, we had produced scFv LR, obtained from a different parental fragment (scFv 3F). LR also showed a similar neutralizing capacity. The simultaneous administration of both scFvs resulted in improved protection, which was translated as a rapid recovery of previously envenomed animals. The crystallographic structure of the ternary complex (scFv LR-Cn2-scFv RU1) allowed us to identify the areas of interaction of both scFvs with the toxin, which correspond to non-overlapping sites. The epitope recognized by scFv RU1 seems to be related to a greater efficiency in the neutralization of the whole venom. In addition, the structural analysis of the complex helped us to explain the cross-reactivity of these scFvs and how they neutralize the venom.

Centruroides baergi is a scorpion species distributed in the biogeographical province of the Balsas Basin in Mexico. Health officials have reported acute envenomation in human populations living on the western side of this scorpion's range, but none in the eastern region. This disparity in toxicity suggested that there may be two distinct species. We used two different approaches, including venom analysis and morphometric specimens from both regions, to test our hypothesis. We performed chromatographic, electrophoretic, and mass spectrometry analysis to identify the known β-toxins involved in the intoxication. The most remarkable finding was the absence of Cb3 β-toxin in the eastern population. Consequently, the LD₅₀ of the eastern population was lower than that of the western population. We analyzed linear and ratio body measurements with parametric and nonparametric statistics to test species limits. These analyses indicated that all putative populations of C. baergi are significantly similar, suggesting that they may represent a single species. Unexpectedly, the population of scorpions in the center of the study area, Suchixtlahuaca, previously identified as C. baergi, showed significant morphological and venom composition differences. We provided empirical evidence of an abrupt change of highly toxic peptides around the 98th meridian that limits populations of Centruroides baergi to the east of Mexico.