“WE HAVE a hospital just across the road, with a store of our antivenoms,” says biologist Nick Casewell. That’s good to know, given that we are in a room stacked floor to ceiling with boxes holding the world’s deadliest snakes. There are rattlesnakes, puff adders, black mambas and more – if it can kill a human, it’s here. With about 250 animals from 40 different species, it’s one of the largest collections of venomous snakes in Europe. And it’s milking time.
Casewell and his colleague Paul Rowley are about to collect the venom of four vipers from equatorial Africa. We are in the Alistair Reid Venom Research Unit, which sends supplies of venom around the world to make antivenom. But Casewell is also working on a project that could save tens of thousands more lives each year.
Looking around, every snake’s box lists its species and the antivenom required if you are bitten. And therein lies the problem. An antivenom only works for a handful of species at most. If you get bitten, you need to know what kind of snake it was and hope that someone nearby has exactly the right concoction to give you. If not, you’re in trouble. Surveys estimate that around 125,000 people die from snakebites every year. The true figure is probably much higher, Casewell says. “Snakebite is a major problem, but the attention it receives is almost nil.”
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Casewell has seen first-hand the devastation bites can cause, when capturing Senegalese saw-scaled vipers for his unit and when setting up a snakebite project in Kenya. “We visited hospitals with patients who had been bitten by spitting cobras. Some of them had horrific wounds,” he says.
Snakes can kill and maim in various gruesome ways, including by paralysing the respiratory system or causing catastrophic tissue death. But more than half of deaths are the result of what Casewell calls “blood disturbances”.
That’s the speciality of the Gaboon viper, which Rowley is just about to release on to the floor to be milked. Symptoms include intense pain, internal bleeding and an extreme drop in blood pressure. Though its venom is not quite as potent as, say, that of a black mamba, Gaboon vipers have the longest fangs of any snake and the deepest bite, and can inject the greatest amount of venom.
Rowley, who has managed this herpetarium for 24 years, uses a hook to take the snake from its box. He always handles the dangerous end and has been bitten three times. It’s a low strike rate, given that he has been milking snakes for all that time. Once the snake is on the floor, Casewell holds it down with a section of plastic pipe attached to a broom handle. It’s the best thing for the job apparently. “I made it in the 90s,” says Rowley. The pair are calm despite the situation. The writhing viper escapes several times before they get it under control.
“Fat-bodied vipers in particular are so strong,” says Casewell. “There’s always a moment when you’ve got the snake restrained using the tools and you have to switch to using your hands. That’s the moment of greatest risk.”
But once Rowley has grasped the snake behind its head, the tension eases slightly. The pair carry the animal to a table where a membrane-covered jar awaits. Rowley touches the snake’s snout to the glass, and its mouth instinctively springs open. Long fangs swing forward and the snake plunges them through the membrane. Thick yellow venom drips from its fangs and pools inside the jar.
Antibody cocktail
Some of this venom will be used to make antivenom the traditional way. This method has barely changed in over a century: you inject venom in non-fatal doses into a horse or sheep, then extract the antibodies it produces. But it’s far from ideal, because the antivenom contains numerous animal proteins that can induce severe allergic reactions in people. “If they weren’t life-saving treatments,” Casewell says, “they would have a hard time passing medical safety standards.”
Casewell and his colleagues are taking a different approach. Though each species’ venom is unique, all contain a cocktail of 50 to 200 proteins, and only 20 or so of those are really harmful. The team is working to identify the key toxins that make you bleed to death. Casewell will then immunise mice with them. The resulting antibodies should combat the lethal effects of any venom from half of all snakebites. “If you’re bitten and you’re bleeding, this one antivenom should save you regardless of the snake,” says Casewell.
And the snakes win too. Using a technique called monoclonal antibody production, he plans to clone the antibody-making cells from the immunised mice to generate a culture that will produce an endless supply of all-round antivenom. That will remove the need to use animals to produce it year after year, and largely solves the allergy problem too. “This type of approach has the potential to completely revolutionise the field of antivenom,” says Casewell.
Back at the venom unit, Casewell and Rowley gently return the viper to its box and transfer the venom to a vial that goes in the fridge. They have three more snakes to milk. But having to work so intimately with such lethal animals is a risk worth taking. “When I see first-hand the patients who are suffering, the destitution and poverty that these people live in and the effect that snakebite has on not only them but their families, it’s a powerful motivator.”
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Nick Casewell is senior lecturer and Wellcome Trust research fellow at the Alistair Reid Venom Research Unit, Liverpool School of Tropical Medicine, UK
This article appeared in print under the headline “Inside the venom factory”
