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Last Updated: Monday, 2 May, 2005, 01:37 GMT 02:37 UK
Search for a snakebite cure
By Caroline Ryan
BBC News health reporter

Saw-scaled viper - Liverpool School of Tropical Medicine
Researchers have the dangerous job of extracting venom
When you come face-to-face with a saw-scaled viper, it's a relief to find it safely contained in a cage.

But people living in tropical areas are not so lucky.

Snake bites cause 125,000 deaths each year. Almost 10 times that number suffer severe, permanent effects from the bites.

Children are particularly at risk because they encounter the snakes as they play and work in the fields and forests where they are found.

The saw-scaled viper is one of 400 of the world's deadliest snakes, kept at the Liverpool School of Tropical Medicine.

Concrete baths

Scientists there are looking at developing new ways of making antivenom.

It is hoped that the ease of DNA production and improved efficiency should make the new antivenoms more commercially viable
Dr Rob Harrison, Liverpool School of Tropical Medicine

They are doing so because, for much of Africa, none is available.

Pharmaceutical companies in Europe have either stopped manufacturing it, or have scaled back production because of low profit margins.

As a short-term measure, the Liverpool team, led by Professor David Theakston, are sending venom from their snakes to factories in South America, which are using their spare capacity to produce antivenom for Africa.

The antidote to a snake-bite is currently produced by repeatedly injecting small amounts of venom into sheep or horses.

There are some villages in west Africa where snake bite is more of a problem than anything else
Dr Rob Harrison

Once the animals have built up a high level of immunity following their repeated exposure to the venom, they are bled, and the therapeutic antibodies they have developed are separated out and treated so the size of the antivenom molecules are reduced.

This helps to reduce the risk of adverse immune reactions in people.

The researchers are aiming to develop antivenoms which will be effective against bites from a number of snakes, instead of just one, as current antivenoms are.

Amputation risk

But people living in areas where snake bites are common have developed their own ways of dealing with them.

There is the 'cut and suck', where the wound is cut open and the blood sucked out. However this doesn't work, particularly if the victim has been bitten by a viper and therefore likely to bleed a lot.

Other remedies without therapeutic value include a concrete bath, used in Sri Lanka and India, where victims are covered in oil and the Black Stone, a porous stone which is placed on top of the wound.

Electric shock therapy has also been found to be ineffective at neutralising the effect of venom, despite its widespread use in Africa and South America.

Dr Rob Harrison, of the Alistair Reid Venom Research Unit at the Liverpool School of Tropical Medicine, says: "There are some villages in west Africa where snake bite is more of a problem than anything else.

"And snake bite victims can take up as many as 70% of hospital beds in some rural hospitals."

When someone is bitten by a snake, the venom may stay in the tissue around the bite, which could lead to scarring - or even tissue death.

Once that happens, a victim may be left with permanent physical damage.

But if the venom gets into the blood stream, the snake venom can be fatal.

And different types of snakes can cause different effects with their bites. Cobra bites lead to paralysis, while vipers cause haemorrhaging.

'Endless supply'

The Liverpool researchers are also investigating more long-term treatment options.

DNA technology offers new hope. They have been able to analyse the genetic make-up of venom, and what parts of the venom cause the pathology.

A gene called jararhagin, an enzyme found in the venom of the Brazilian pit viper, Bothrops jararaca, that causes haemorrhaging, was injected into the skin of mice, prompting the mice to generate antibodies that neutralized about 70% of the haemorrhagic activity of the viper venom.

The scientists are now planning to develop the technique further so that mice will produce human-type antibodies.

Those antibodies would then be extracted and fused with other cells to "manufacture" a potentially limitless supply of anti-venom.

Encouraged by these results, Dr Harrison's team is now isolating the DNA of toxins from the venom of saw-scaled vipers, puff adders and desert horn vipers, responsible for the majority from the 20,000 deaths from snake-bites in Africa each year.

They found that the DNA encoding these venom toxins looked very similar, raising the hope that one antibody could be used as the basis for anti-venom which is effective against a number of snake species, rather than just one.

Dr Harrison said: "Our approach is to scientifically examine the major toxins in venoms of the most medically-important vipers in Africa, and isolate the genes that encode those toxins.

"Then, by using new DNA-immunisation techniques, we would generate antibodies to those parts of the venom toxins that are identical in all the venomous snakes of that region.

"This new, rationally designed, antivenom would be much more dose-effective than conventional antivenoms at neutralising envenoming by any of the snakes in that region."

He added: "It is hoped that the ease of DNA production and improved efficiency should make the new antivenoms more commercially viable in Africa than conventional systems."

And it may not be all bad news in relation to snake venom itself.

Scientists have developed two anti blood-clotting drugs, Aggrastat and Ancrod, based on proteins found in the venom, and more venom-based drugs are being investigated.

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