Thrombocytopenia induced by viperid snake venoms in a murine model and its neutralization by a polyvalent antivenom.

Thrombocytopenia is a common manifestation in viperid snakebite envenomings, contributing to systemic bleeding and hemodynamic alterations. Despite its relevance, this effect is not evaluated when assessing the neutralizing ability of antivenoms. In this study we present an in vivo method in mice for the quantification of thrombocytopenic effect. Representative venoms of Costa Rican viperid snake genera (Atropoides, Bothrops, Bothriechis, Cerrophidion, Crotalus, Lachesis, Metlapilcoatlus, and Porthidium) were administered by the intramuscular route in mice and platelet counts were carried out 3 h after envenoming. Only the venoms of Bothrops asper and Bothriechis lateralis induced a significant drop in platelet numbers as compared to controls receiving saline solution. The polyvalent antivenom used in Central America was effective in the neutralization of the effect, even in the case of B. lateralis venom, which is not included in the immunizing mixture. In the case of B. asper venom, a C-type lectin-like (SNACLEC), which indues platelet aggregation in the presence of plasma, is responsible for the thrombocytopenic effect. Thus, an in vitro test was designed to assess the efficacy of the antivenom, based on the neutralization of the in vitro aggregating effect of the SNACLEC and of crude venoms of B. asper and B. lateralis in which proteinase activity was inhibited to avoid the coagulation of plasma. This in vitro assay could be useful for assessing antivenom efficacy against thrombocytopenic components of venoms. It is suggested that the neutralization of thrombocytopenic effect of venoms by antivenoms be added to the list of supplementary tests used in the preclinical assessment of antivenom efficacy.