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The immune response involves a complex repertoire of innate and adaptive responses to foreign agents in the organism. The present review focuses on the immune response to snake venoms, including those occurring in snakebite accidental envenomation, experimental vaccination and animal hyperimmunization for snake antivenom production. The following aspects are considered: (a) the structural characteristics of snake toxins and their relationship to immunogenicity, (b) the effects that factors such as administration route, venom dose, type of adjuvant, and individual and species characteristics of the immunized animal have on the immune response, (c) the initial venom-induced inflammatory response, (d) the process by which specific antibodies towards individual toxins are produced, and (e) the techniques currently used to evaluate the antibody response. Understanding the immune response to snake venoms is highly relevant for improving antivenom production and for gaining a more complete view of snakebite envenoming.

A randomized double-blind clinical trial in 39 patients envenomed by Bothrops atrox in Antioquia and Chocó, Colombia, was performed to compare the efficacy and safety of 2 equine-derived antivenoms prepared at Instituto Clodomiro Picado, University of Costa Rica. Twenty patients received a monovalent anti-B. atrox antivenom (group A) and 19 patients were treated with a polyvalent (Crotalinae) antivenom (group B). Both antivenoms were equally efficient in the neutralization of the most relevant signs of envenoming (haemorrhage and blood clotting time alteration). Fourteen patients (36%) presented early adverse reactions to antivenoms and no significant difference between the 2 groups was observed. Urticaria (18%) was the most frequent early adverse reaction and there was no life-threatening anaphylactic reaction. Based on clinical criteria and serum venom levels, estimated by an enzyme immunoassay, 15 patients were classified into 2 groups: mild and moderate/severe envenoming. With the antivenom doses used in this study (3, 6 and 9 vials for mild, moderate and severe envenoming, respectively), both antivenoms were equally efficient in clearing serum venom levels within the first hour of treatment, and the levels remained below the lower limit of venom detection for 24 h. Antivenom concentration in serum remained high for up to 24 h after antivenom infusion, suggesting that an excess of antibody in relation to circulating antigen had been administered.

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