NEW SCIENTIST (UK) 06 June 06 New antivenom could save more snakebite victims (Debora MacKenzie)

A snakebite antivenom has been developed that is more powerful than conventional antidotes and works even when it is unclear exactly what species of snake has bitten the victim.

Snakebites kill tens of thousands of people each year, yet supplies of traditional antivenom are drying up. The inventors of the new antidote hope it will be taken up in the poor countries where it is most needed.

Snake venom contains a complex cocktail of tissue-destroying enzymes. The only antidote till now has been the antibody-rich serum extracted from the blood of horses after they have been injected with venom milked from snakes.

In recent years, big drug companies have stopped making antivenom as it is increasingly unprofitable: the serum needs to be purified to meet stringent safety standards, animal rights activists object because the horses suffer, and most of the people who need the product can't afford it. Serum against African snakes is now especially scarce.

Snake-free venom

Simon Wagstaff and colleagues at the Liverpool School of Tropical Medicine in the UK have now made a serum without using snake venom. Instead, they started with the DNA of the carpet viper, which is responsible for the majority of snakebite deaths in west Africa, and looked for the genes that are active when the snake is refilling its venom sacs.

A dozen of these genes code for metalloprotease enzymes that destroy blood vessels and cause haemorrhaging. From these genes they created a “consensus” sequence that resembles as closely as possible all the different genes.

From this generic gene they took seven DNA stretches that code for parts of the outside of the protein molecules and should therefore elicit antibody responses in the body, and joined these together to make a single strand.

Sure enough, when they injected this synthetic DNA into mice, the animals made antibodies to these parts of the protein. When serum extracted from these animals was tested on other mice it was more powerful than classic serum against carpet viper venom, but also against other west African vipers, and even a viper from north Africa.

This generic action is important, as classic antivenom works best against the species from whose venom it is prepared, yet victims may not know which snake has bitten them. Also, because the serum produces specific antibodies, rather than the much larger range of antibodies in classic serum, it is less likely to provoke an allergic reaction.

Western companies are unlikely to snap up Wagstaff's technique, however, as it still requires the use of large animals such as horses to produce viable amounts of serum.

But Wagstaff told New Scientist that he hopes producers in developing countries will try making serum using the team’s technique.

Journal reference: PLoS Medicine, DOI: 10.1371/journal.pmed.0030184



http://www.newscientist.com/article/dn9277-new-antivenom-could-save-more-snakebite-victims.html

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