Imma Perfetto
Cosmos science journalist
In India, the snakebite capital of the world where about half of all snakebite deaths occur, a single deadly serpent causes more death and disability than any other.
Russell’s viper (Daboia russelii) is found across the Indian subcontinent, but its venom varies wildly between regions. This means that a person bitten in one place will experience different symptoms to someone bitten elsewhere.
New research has found that a combination of climatic factors – temperature and precipitation – is partly driving this variation.
The scientists say their findings could be used to predict the clinical symptoms of Russel’s viper bites across different regions to inform clinicians to select the most appropriate treatment.
Snake bites, which kill an estimated 81,000–138,000 people each year, are a major global public health challenge. The study, which is published in PLOS Neglected Tropical Diseases, provides new insights into the complex evolutionary adaptations of what might be the most clinically important venomous snake in the world.
Assistant Professor Kartik Sunagar, the study’s corresponding author who leads the Evolutionary Venomics Lab at the Indian Institute of Science, says that Russel’s viper kills and maims more people than any other snake species.
“As a result, it is important to precisely unravel the composition, activity, and potency of Russell’s viper venoms and understand the role of biotic and abiotic factors in shaping them,” says Sunagar.
“Recent studies from our lab have shed light on the influence of biotic factors, such as developmental shifts in diet, on Russell’s viper venom composition and toxicity.”
However, the effects of abiotic, or environmental, factors have remained unstudied until now.
Sunagar and his colleagues analysed venom samples from 115 snakes collected from 34 locations across India. They then used historical climate data to understand the relationship between venom composition and the local climate, which varies considerably even in short distances across the landmass.
“Here, we highlight, for the first time, the role of climatic conditions, such as temperature, humidity and rainfall, in driving the biochemical functions of Russell’s viper venoms.”
Experiments revealed that Russel’s viper venom from dryer regions of India contain more protein-degrading enzymes, which are a major component of venom responsible for the most severe clinical symptoms.
Other venom components were unaffected by climate.
The researchers used this data to create a map of expected venom types across Russell’s viper’s range in India, which could be used to predict the clinical symptoms of snake bites in different regions.
“Though the mainstay treatment for Russell’s viper bites is the administration of polyvalent antivenom, the effectiveness of the antivenom therapy is affected by the complexity of venom variability among individual snakes of this species across its distribution,” the authors write in the study.
“These predictive maps will guide us in unravelling the geographic venom variation in a species and provide valuable insights into localities where a particular targeted therapy, such as a toxin-specific recombinant antibody or a species-specific antivenom or small molecule inhibitor drug, could be deployed.”
