The fight against snake bites

Venomous snake bites are responsible for 138,000 deaths every year around the world, but could some disarmingly simple interventions help to save lives?

"In the monsoon, the fields are overgrown with weeds," says Tukaram Rao, a farm labourer from the village of Rathnapuri in Karnataka, southwest India. "We have to walk out in the midst of those at night to turn on the water pump for the field. Sometimes if the water pipes are disjointed, we walk alongside the water pipe, feeling with our hands to fix it."

Like many farm workers in rural India, Rao and his neighbours tend to get around barefoot. But lurking in the thick undergrowth is something more worrisome than leaking water pipes. This is the perfect habitat for the Russell's viper, a large, earth-coloured, highly venomous snake found across much of India and parts of South Asia.

These snakes are active during the night and are masterful ambush predators, remaining motionless before striking their prey. They mainly hunt rodents or small frogs that scurry into their path in the fields where they forage – these snakes are not interested in humans. Yet they account for more bites and deaths in India than any other species of snake. The Russell's viper is estimated to be responsible for as many as 43% of snake bites in India and is responsible for 30-40% of snake bites in Sri Lanka.

Much of the reason for this is how they hunt. Sluggish to the point of immobility, they inch their way through the grass, their green and brown camouflage making them almost invisible in daylight. At night, they are impossible to spot. For farmers working in paddy fields or among overgrown plants, the snakes are easy to step on or disturb. And when they feel threatened, the Russell's viper becomes aggressive, striking out at random with its fangs.

There are around 2.8 mn cases of snake bites in India each year and 50,000 deaths. In the past two decades, more than 1.2 million people have died from snake bites in India alone. Globally snake bites are thought to cause between 81,000 and 138,000 deaths a year. But the true impact of snake bites is greater still. A bite from a venomous snake can leave survivors with life-changing injuries. It is something Rao has seen first-hand.

"A farmer was recently weeding his turmeric field when he got bit on his leg and the flesh around his ankle rotted away," he says. "The rot spread to his knee. Now he is unable to do any work." Doctors were forced to amputate part of the man's leg. "Three times as many victims – around 400,000 per year – are left with long-term disabilities such as limb necrosis leading to amputations, disfigurement and blindness," says Laura-Oana Albulescu, who studies snake venom at the Liverpool School of Tropical Medicine in the UK.

The global health burden created by snake bites is thought to be huge. Of the estimated 4.5 mn people who are bitten by snakes worldwide each year, around 2.7 mn men, women and children are left seriously injured, according to the Global Snakebite Initiative.

"Snake bites are a far bigger problem than many people realise," explains Leslie Boyer, founding director of the Venom Immuno chemistry, Pharmacology and Emergency Response ( Viper) Institute at the University of Arizona in the US. The WHO considers snake bites to be such a burden on some communities that they recently classified snake bite envenomation – where venom is injected by a bite – as a neglected tropical disease.

Snake bites are now recognised as one of the world's most important neglected health problems and one that disproportionately affects poorer communities.

But should snake bites be such a large problem? "We've known how to make antivenoms for about 120 years," says Boyer, referring to some of the work by scientists at the Pasteur Institute in France, the Lister Institute in England and the Butantan Institute in Brazil. While many antivenoms are effective, the complex nature of snake venom can make treatment difficult. Access to antivenom can be patchy and treatments with it can be expensive. This has led some to seek other ways of tackling the health burden caused by snake bites.

Rao and his neighbours are now involved in one such project aimed at helping the communities most at risk from snake bites to protect themselves. And the solution is deceptively simple – they are being given boots. "Many people in rural parts of India are walking around in the dark without footwear," says Sumanth Bindumadhav, senior manager of the wildlife, disaster response and Dharwad program at the Humane Society International in India. "Over 90% of bites occur when people step on a snake without even seeing them." His organisation has handed out more than 400 rubber boots and 200 solar lamps to residents in Rao's village and the surrounding area. "Putting a light in people's hands and footwear that will cover up to the ankle can seem simple, but it makes a big difference," says Bindumadhav. "The Russell's viper has some of the longest fangs of any snake in India, but it is very hard for them to penetrate gumboots. Preventing snake bites is better than treating them."

Snake venom is a complex cocktail of toxins that varies from species to species.

Hospitals in India primarily use a polyvalent (or multipurpose) antivenom as an antidote against the "big four" snakes that cause the majority of bites – the spectacled cobra, the common krait, saw-scaled viper and the Russell's viper. It is produced using venom from these four snakes. But India has more than 60 venomous species of snake and there is no specific antivenom against most of them. Instead, the "big four" antivenom is often used as a general snake bite treatment. Recent research has found, however, that it is largely ineffective against the venom of other important snakes in the country.

To compound the problem further, other research has shown that even among the big four, the toxins in the venom can vary depending on where in the country they are. It means that antivenom produced using snakes in southern India might be less effective against the venom from the same species in the north or those in Sri Lanka or Nepal.

"These are never going to be one-sizefits-all treatments," says Boyer. "But they could be a bridge to antivenom. It could help someone survive the trip to a hospital where they stock antivenom or protect a limb from necrotising damage."