Viper envenomation in Central and Southeastern Europe: a multicentre study.

INTRODUCTION: Snakebite incidence varies across Europe. However, there is limited research from Central and Southeastern Europe. These regions are notable for the presence of the common European adder (Vipera berus) and the more venomous nose-horned viper (Vipera ammodytes). No standard European antivenom protocol exists. The aim was to assess the epidemiology and treatment of viper bites in this region, focusing on a comparison of bites from Vipera berus and Vipera ammodytes. METHODS: We conducted a prospective multicenter study in Central and Southeastern Europe from 2018 to 2020. This study included poison centres and toxicology-associated hospital wards in Poland, the Czech Republic, Slovakia, Hungary, Slovenia, Croatia, Serbia, and Bulgaria. The following data were collected: age, gender, Vipera species, snakebite site, clinical picture, laboratory results, Audebert's clinical severity grading score, and antivenom therapy. RESULTS: The annual incidence of viper bites in Central and Southeast Europe was estimated at 2.55 bites per million population. Within their respective geographical distribution areas, the incidence of Vipera ammodytes bites (1.61 bites per million population) was higher than Vipera berus bites (1.00 bites per million population). Patients bitten by Vipera ammodytes more frequently reported local pain and developed thrombocytopenia. Antivenom treatment was more commonly administered in Vipera ammodytes bites (72%) compared to Vipera berus bites (39%). The incidence of Vipera ammodytes bites treated with antivenom within its geographical distribution area was three times higher than Vipera berus bites treated with antivenom (1.16 bites per million population versus 0.39 bites per million population). No deaths were reported. CONCLUSIONS: The estimated incidence of viper bites in Central and Southeastern Europe is at least 2.55 per million population. Vipera ammodytes bites are more common and severe, characterized by higher frequencies of pain and thrombocytopenia. Antivenom is needed more often for Vipera ammodytes bites. It is vital that enough European Medicines Agency-approved Vipera ammodytes antivenom is produced and offered affordably.

Intravenous Vipera berus Venom-Specific Fab Fragments and Intramuscular Vipera ammodytes Venom-Specific F(ab')2 Fragments in Vipera ammodytes-Envenomed Patients.

Vipera ammodytes (V. ammodytes) is the most venomous European viper. The aim of this study was to compare the clinical efficacy and pharmacokinetic values of intravenous Vipera berus venom-specific (paraspecific) Fab fragments (ViperaTAb) and intramuscular V. ammodytes venom-specific F(ab')2 fragments (European viper venom antiserum, also called "Zagreb" antivenom) in V.ammodytes-envenomed patients. This was a prospective study of V.ammodytes-envenomed patients that were treated intravenously with ViperaTAb or intramuscularly with European viper venom antiserum that was feasible only due to the unique situation of an antivenom shortage. The highest venom concentration, survival, length of hospital stay and adverse reactions did not differ between the groups. Patients treated with intravenous Fab fragments were sicker, with significantly more rhabdomyolysis and neurotoxicity. The kinetics of Fab fragments after one or more intravenous applications matched better with the venom concentration in the early phase of envenomation compared to F(ab')2 fragments that were given intramuscularly only on admission. F(ab')2 fragments given intramuscularly had 25-fold longer apparent total body clearance and 14-fold longer elimination half-time compared to Fab fragments given intravenously (2 weeks vs. 24 h, respectively). In V.ammodytes-envenomed patients, the intramuscular use of specific F(ab')2 fragments resulted in a slow rise of antivenom serum concentration that demanded their early administration but without the need for additional doses for complete resolution of all clinical signs of envenomation. Intravenous use of paraspecific Fab fragments resulted in the immediate rise of antivenom serum concentration that enabled their use according to the clinical progress, but multiple doses might be needed for efficient therapy of thrombocytopenia due to venom recurrence, while the progression of rhabdomyolysis and neurotoxic effects of the venom could not be prevented.

Comparison of Preclinical Properties of Several Available Antivenoms in the Search for Effective Treatment of Vipera ammodytes and Vipera berus Envenoming.

Snakebites are a relatively rare medical emergency in Europe. In more than half of the annual cases caused by Vipera ammodytes, Vipera berus, and Vipera aspis, immunotherapy with animal-derived antivenom is indicated. Among eight products recently identified as available against European medically relevant species, only Zagreb antivenom, Viperfav, and ViperaTAb have been used almost exclusively for decades. Zagreb antivenom comprises V. ammodytes-specific F(ab')2 fragments. Viperfav is a polyspecific preparation based on F(ab')2 fragments against V. aspis, V. berus, and V. ammodytes venoms. ViperaTAb contains Fab fragments against the venom of V. berus. In 2014 the production of Zagreb antivenom was discontinued. Additionally, in the period of 2017 to 2018 a shortage of Viperfav occurred. Due to a lack of the product indicated for the treatment of V. ammodytes bites, other antivenoms were implemented into clinical practice without comparative assessment of their eligibility. The aim of our work was to identify a high-quality antivenom that might ensure the successful treatment of V. ammodytes and V. berus bites at the preclinical level. Differentiation between bites from these two species is difficult and unreliable in clinical practice, so the availability of a unique antivenom applicable in the treatment of envenoming caused by both species would be the most advantageous for Southeastern Europe. Zagreb antivenom, Viperfav, and ViperaTAb, as well as Viper venom antitoxin for V. berus envenoming and the in-development Inoserp Europe, which was designed to treat envenoming caused by all medically important European snakes, were comparatively tested for the first time. Emphasis was placed on their physicochemical properties, primarily purity and aggregate content, as well as their in vivo protective efficacies. As Zagreb antivenom is no longer available on the European market, Viperfav is the highest-quality product currently available and the only antivenom whose neutralisation potency against V. ammodytes and V. berus venoms was above regulatory requirements.