With its diverse landscapes, ranging from arid scrublands to rocky plains and rain-soaked forests to urbanized settlements, India is home to many venomous snakes. About one million snakebites occur each year, resulting in as many as 58,000 deaths.1 A majority of these deaths are due to Russell’s vipers.2
Snakebites across regions lead to different symptoms because of varying composition and activity of enzymes in the venom.3 “We have previously shown that diet influences the venom of Russell’s vipers,” said Kartik Sunagar, an evolutionary biologist at the Indian Institute of Science. “We were keen to see if the environment or abiotic factors also [play] a role.”
Sunagar and his team recently found that climate influences the biochemical composition of Russell’s viper venom, with snakes from drier regions having higher activity of protein-degrading enzymes that damage human tissue.4 Their results, published in PLoS Neglected Tropical Diseases, could help scientists predict the clinical symptoms of snakebites in different locations and help doctors provide appropriate therapies.
Russell’s viper bites are usually treated with polyvalent antivenom that can neutralize the venoms of multiple snakes, but its efficacy is affected by variation in venom composition.5
For their study, Sunagar and his team collected venom samples from 115 Russell’s vipers across different biogeographic zones in India. Biochemical assays revealed that the activity of various toxins—such as enzymes that break down proteins, phospholipids, and amino acids in human cells to cause symptoms—varied significantly between venoms from different regions.
“This is very comprehensive data, nicely analyzed in a systematic way,” said Christiane Berger-Schaffitzel, a biochemist at the University of Bristol who was not involved in the research. “It's absolutely important to understand the local variation of venom, because it has a very immediate consequence for the antivenom efficacy that is administered,” she added.
The researchers investigated a link between venom composition and the local weather at sampling sites using historical climate data. They observed that temperature and rainfall partly explained the variation in venom makeup. Among these components, protein-degrading enzyme activity showed the highest correlation with climate. Phospholipase activity did not show such a strong link. In contrast, climatic variation did not affect amino acid oxidase activity.
Using this data, Sunagar and his team generated a predictive map showing how Russell’s viper venom composition might vary across India. “If you have these predictive maps, you already know which toxins might be abundant [in a specific region],” said Sunagar. “So, you can basically tailor therapies depending on the activity.”
For instance, their maps indicated that people bitten by Russell’s vipers in the humid northeastern plains and coastal regions may need therapies targeting phospholipases in the venom. In contrast, drugs targeting protein-degrading enzymes may be most efficient to treat snakebites in the arid regions of northwest India.
Neither Sunagar nor Berger-Schaffitzel were surprised by the link between climate and venom composition. “Because, of course, with the climate, the prey and the predators for the snakes change, and they have evolved to their environment,” said Berger-Schaffitzel. Nevertheless, she noted the importance of Sunagar and his team’s analyses. “The same should be done for [other regions] where snakebite and envenoming is a problem.”
According to Sunagar, the study is not without limitations. While their analyses highlight a link between abiotic factors and the observed venom compositions, their model does not account for the influence of biotic factors such as the snakes’ diet and predator pressure. He also noted that they worked with a limited sample size of 115 snakes. “In the future as we keep collecting items for our studies, if we keep updating this model, it will probably become more accurate.”
- Chakma JK, et al. White paper on venomous snakebite in India. Indian J Med Res. 2020;152(6):568-574.
- Suraweera W, et al. Trends in snakebite deaths in India from 2000 to 2019 in a nationally representative mortality study. eLife. 2020;9:e54076.
- Kalita B, et al. Proteomic analysis and immuno-profiling of eastern India Russell's viper (Daboia russelii) venom: Correlation between RVV composition and clinical manifestations post RV bite. J Proteome Res. 2018;17(8):2819-2833.
- Sarangi N, et al. Significant serpents: Predictive modelling of bioclimatic venom variation in Russell's viper. PLoS Negl Trop Dis. 2025;19(4):e0012949.
- Senji Laxme RR, et al. Biogeographic venom variation in Russell's viper (Daboia russelii) and the preclinical inefficacy of antivenom therapy in snakebite hotspots. PLoS Negl Trop Dis. 2021;15(3):e0009247.
