Introduction: Tityus obscurus Gervais, 1843 (Scorpiones: Buthidae) is a senior synonymous of T. paraensis Kraepelin, 1896 and T. cambridgei Pocock, 1897. It is widely distributed in the Brazilian Amazon basin and is considered the most important species responsible for scorpion stings. There were several differences in the clinical manifestations of envenomation by this species. Objective: To contribute for the knowledge of scorpionism by T. obscurus in Brazilian Amazon. Methods: We describe and compare the clinical and epidemiological findings of envenomation by T. obscurus in eastern and west areas of the state of Para. The composition of the venom, morphometric measures and DNA analysis of specimens captured were also compared between study areas. Results: From Jan 2008 to Jul 2010 were included 48 patients with confirmed envenomation by T. obscurus. Most of them came from the eastern region (70.8%). Median age groups were similar in both areas. Most scorpion stings took place during the day and occurred significantly on the upper limbs. The time between the sting and admission to the health center was less than three hours in both areas. Most eastern patients had local manifestations while in the west, systemic manifestations predominated. Local symptoms were similar in both areas, but systemic signs and symptoms were more common in the west. Symptoms frequently observed at the sting site were local and radiating pain, paresthesia, edema, erythema, sweating, piloerection and burning. The systemic manifestations were higher in patients from the west. Furthermore, neurological symptoms, such as general paresthesia, ataxia, dysarthria, myoclonus, dysmetria, and electric shock-like sensations throughout the body were reported only by patients from the west. Mitochondrial gene 16S rRNA showed a polymorphism of 9.06% with divergence from 9.7 to 11% forming two distinct at Neijgbor-Joining and Máxima Parcimônia. There were 18 and 20 specimens captured in west and in eastern regions, measuring between 62.15 to 85.24mm. The largest specimens were captured in the west. Multivariate analysis showed a significant difference between specimens from both sites. The analysis of venom by mass spectrometry and high performance liquid chromatography showed significant differences in both the composition and concentrations of venom components. The venom of specimens captured in west showed a high concentration of compounds with affinity for K+ and Na+ channels. Conclusion: There are a regional diversity in several aspects of envenomation by T. obscurus Gervais, 1843, in the state of Para. The geographical separation promotes, probably, a speciation of specimens, forming two distinct lineages, with 16S rRNA divergences and different length, chemical composition of venom and clinical manifestations of envenomations. The authors suggest a taxonomic review of this species.
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