Envenomation by the scorpion Tityus breweri in the Guayana Shield, Venezuela: report of a case, efficacy and reactivity of antivenom, and proposal for a toxinological partitioning of the Venezuelan scorpion fauna.

OBJECTIVES Scorpion envenomation is a common public health problem in Venezuela. We report an envenoming case by Tityus breweri, endemic to the Guayana Shield, southeast Venezuela, and the outcome of its treatment with antivenom anti-Tityus discrepans. Toxin composition and antigenic reactivity of T breweri venom were also explored. T breweri distribution range was re-evaluated. METHODS Clinical signs and symptoms in an adult male were recorded after envenoming and treatment with antivenom. Toxin composition and antigenicity of T breweri venom were investigated by polyacrylamide gel electrophoresis, immunoblotting, and mass spectrometry. T breweri distribution range was reassessed by mapping new records of the species. RESULTS The moderately severe case (a 21-year-old man) presented autonomic manifestations, including cardiopulmonary and gastrointestinal effects. Full recovery was achieved after anti-T discrepans antivenom administration. T breweri venom contains toxins in the 6-8 kd range that affect voltage-sensitive sodium channels. Based on new records, T breweri distribution area reaches 12 155 km.(2) Inclusion of southeast Venezuela as an endemic area of scorpionism prompted the examination of clinical, immunological, and phylogenetic evidence for suggesting a partitioning of the Venezuelan Tityus fauna into toxinological provinces. CONCLUSIONS The severity of the case reinforces categorization of the Guayana Shield region as a macroendemic area of scorpionism in Venezuela and allows classification of T breweri as a species of medical importance, with toxins immunologically related to central-eastern Venezuelan Tityus. Partitioning of the territory incorporating multiple criteria may help health authorities establish and implement preventive and therapeutic measures for scorpion envenoming in this region.