Snakebite kills approximately 138,000 people and causes 400,000 disabilities each year, primarily in poor rural communities in low- and middle-income tropical and subtropical countries. The WHO has pledged to reduce this burden by 50% by 2030 but there is limited knowledge of how, when, and where humans and snakes interact.

In the new study, researchers used public and private databases, citizen science platforms, museum records, scientific literature, and expert observations to model the habitats of all 508 medically important venomous snake species at about 1 km resolution. 

Snake and human populations overlap?

The team used these models to generate estimates of how snake and human populations currently overlap, as well as to project how that might shift by 2050 and 2090 due to climate change.

The researchers found that current snake-human overlap is highest across much of sub-Saharan Africa and South and Southeast Asia—regions already known to bear the greatest snakebite burden. 

However, under climate change, there are also notable increases in snake-human overlap across the Indian subcontinent, eastern North America, and parts of China. Most snakes were projected to have a general trend toward higher latitude range distributions but the extent varied by species. 

The four species with the highest and most certain predicted increases in human overlap by 2090 were the black-necked spitting cobra, Naja nigricollis, the many-banded krait (Bungarus multicinctus), the cottonmouth (Agkistrodon piscivorus), and the copperhead (Agkistrodon contortrix). 

Many species across Congo, Amazon and Southeast Asia

Many species across the Congo and Amazon basins and Southeast Asia, especially those with already small ranges, were predicted to show net decreases in range size, raising conservation concerns; However, in Africa, the wide-ranging puff adder (Bitis arietans), which currently causes a substantial number of bites, was also predicted to lose much of its current range.

 “Our predictions can be used to decide where to stockpile which antivenom, how to ensure adequate capacity of individual health facilities, how to improve health care accessibility of remote at-risk communities, and where to focus conservation efforts for threatened snake species,” the authors say.

The authors add: "Before this study surprisingly little was known about the exact distribution of many medically important snakes, even some widespread ones that cause many bites...[a] big reason snakebite is considered a 'neglected' tropical disease is that we know so little about exactly how many people get bitten and where, despite the enormous burden these bites cause in many countries."

They conclude: "The first step in helping victims of snakebite is to know where people and snakes interact the most so we can get support to the right places and the right people, often in remote rural communities."