Indigenous venomous snakebites in Switzerland: analysis of reports to the National Poisons Information Centre over 22 years.

Abstract

Two venomous snakes, the asp viper (Vipera aspis) and the common adder (Vipera berus) are native to Switzerland. Bites by both vipers cause mainly local effects, but systemic envenomation is possible. We analysed all calls concerning indigenous venomous snakebites recorded at the Swiss National Poisons Information Centre between 1997 and 2018, including all cases with identification by a herpetologist, and/or with compatible symptoms and circumstances of the exposure. During the study period, 1,364 cases concerned snakebites. One third (466; 34%) were attributed to indigenous vipers. In 243 (52%) patients, medical follow-up information was available, with good causality between exposure and symptoms in 219 (90%) patients. Vipera aspis was identified in 77 of the cases (35%), Vipera berus in 54 (25%), and not further specified vipers in 88 (40%). In over two thirds of the 219 cases (155, 71%) adult patients were affected (male 109, female 46; median age 43 years [range 16-90]). Sixty-four patients were children (male 47, female 16; median age 11 years [range 1.3-15.9]). The highest occurrence of bites was in the summer months. In the majority of patients, the clinical course was mild (94; 43%) or moderate (80; 36%); a lower proportion was either asymptomatic (17; 8%) or exhibited severe symptoms (28; 13%). There were no fatalities reported. The most frequent symptoms were local effects at the bite site with mild (100; 46%) to moderate (56; 25%) swelling, pain (65; 30%) and redness (51; 23%). Gastrointestinal symptoms including nausea (31; 14%), vomiting (47; 22%) and abdominal pain (25; 11%) were also common. Other systemic symptoms included cardiovascular effects (e.g., hypotension (20; 9%) or shock [6; 3%]), neurotoxicity (e.g., visual impairment [5; 2.3%]) and haematotoxicity (e.g., coagulopathy [11; 5%]). Seven (3.2%) patients developed anaphylactic reactions. Antivenom was administered in only 20% (24 with moderate and 19 with severe symptoms) with good resolution of symptoms. The mean duration of hospitalization was 2 days (0-12 days). Snakebites in Switzerland can result in severe symptoms, sometimes necessitating antivenom treatment.