Species-specific climate and agricultural determinants of viper bite risk in rural Sri Lanka call for targeted prevention approaches.

Ecological drivers of snakebite risk are expected to differ between sympatric species, yet few studies have directly tested this. We compared meteorological and agricultural drivers of bites from Hypnale hypnale (hump-nosed viper) and Daboia russelii (Russell's viper) in the dry zone of Sri Lanka. We analysed 424 authenticated viper bites (313 H. hypnale; 111 D. russelii) from a prospective cohort in Anuradhapura (2018-2022), restricted to bites within 15 km of a central meteorological station. Monthly bite counts were correlated with six meteorological parameters using Spearman's rank-order correlation and negative binomial regression. Hypnale hypnale bites were predominantly peridomestic (57%) and occurred year-round, while 39% of D. russelii bites occurred on farmland. Daboia russelii victims were predominantly male (75.5%), sustaining foot bites in 93.7% of cases. Maximum relative humidity was the strongest meteorological predictor of H. hypnale bite counts (Incidence Rate Ratio 1.13 per 1% increase, heteroscedasticity and autocorrelation consistent-corrected p=0.042); minimum temperature showed a directionally consistent inverse association. Daboia russelii bite counts showed no significant meteorological associations, though ambient temperature shifted bites toward nocturnal hours under thermally suppressive conditions. Marked suppression of D. russelii bites during COVID-19 travel restrictions, combined with agricultural calendar alignment, supports occupational agricultural exposure as the primary population-level risk driver. Our findings suggest that two sympatric vipers operate through fundamentally different risk pathways - H. hypnale risk is climate-driven (humidity and temperature), whereas D. russelii risk is governed by occupational agricultural exposure. Species-specific prevention strategies are essential.