Health: Blood of sheep protects against tongue of viper: There may be no rattlesnakes in Wales, but researchers on a small Carmarthen farm may save some of the two million people worldwide bitten by snakes each year. Jeremy Hart reports

Thomasville, Georgia is the 'Rattlesnake Capital of America' - the centre of America's snake belt. Snakes are found everywhere, from suburban garages to sugar cane fields. A nearby town even has a rattlesnake round-up, where the serpents are gathered annually to have their lethal venom milked.

The chances of being bitten in the UK by a poisonous snake may be low, but with more British people travelling to America, Australia and West Africa, their lack of knowledge may put them more at risk.

In the leafy Georgia town, the local hospital treats a snakebite victim every fortnight. Thomasville may be in the thick of the action, but it is far away on the virtually snake-free hills of south Wales where the most radical advances in antivenin technology in 55 years are being made.

The clue to the revolution is in the fields of a 250-acre farm near Carmarthen, where 2,000 sheep graze in preparation for a monthly donation of blood. Their blood bears what is claimed to be the purest antidote to the world's deadliest snakes.

For almost a century virtually all antivenins have been produced by injecting horses with progressively large amounts of venom and then extracting the resulting antibodies.

The horse's reaction to the venom is very powerful and stimulates a specific immunoglobulin, or antibody, IgG(T). The 'T' is for toxin and a high proportion of patients given snake-bite serum are allergic to it. Figures for an adverse reaction rate range from 10 to 80 per cent, with experts settling at around 40 per cent. This can vary from a rash or asthma- type attack to death in extreme cases.

'Some people do die from antivenin, although we haven't lost anyone,' says Dr Ed Hall, who treats over 20 cases of snakebite a year at a Thomasville hospital.

Using sheep, which do not produce the 'T' immunogloblin that causes the side-effects, was the brainchild of John Landon, professor of chemical pathology at St Bartholomew's Hospital, London, whose research company, Therapeutic Antibodies Ltd, has a budget of pounds 10m for its antivenin programme.

'Antivenoms were first named by a Frenchman, Albert Calmette, in 1896. He gave increased amounts of venom to pigeons, which developed an active immunity to the toxin,' Professor Landon explained.

Other scientists proved that if you injected the blood into another animal you could get passive immunity. Horses were used as they were the animal most widely available.

'At that time immunotherapy had a high incidence of side-effects. Almost everyone then would develop serum sickness, which affected the kidneys and the skin,' Professor Landon said. 'Occasionally they died when they were given the injection.' Even now, some doctors prefer to chance a patient's recovery to nature.

Horse antivenin has been improved and purified since then, reducing the allergy risk. But Professor Landon claims that his sheep antivenin, at about pounds 1,000 a treatment, will have only a 1 per cent incidence of allergic reaction.

Each species of poisonous snake has its own brand of venom, so the Carmarthen sheep are being used to produce antivenins for many different species. These are then sent all round the world: to Nigeria, Sweden, Saudi Arabia, Sri Lanka and the United States.

Dr Hall, in Thomasville, is one the experts involved in the trials, in his case using rattlesnake antivenin. 'As yet it is unproven, it doesn't even have a name. But we have tested it on seven or eight patients and it works great,' he said.

'The problem has been because this is such a small market without much pharmaceutical interest,' said Professor Landon, whose first Welsh laboratory was a milking parlour and a flock of 25 sheep.

The market may be comparatively small in terms of profit but up to two million people a year are bitten by poisonous snakes. One hundred thousand die and three times that are permanently affected. In Britain, there is a one-in-a-million chance of being killed by a snake. The adder, our only venomous snake, kills just once a decade. But in countries such as Nigeria, where one in 10 hospital beds are occupied by snakebite victims, the need for radical and rapid new antivenin is acute. 'Most of the bites are from the carpet viper, which is only 10 inches long, but enjoys biting you. It is unusually aggressive,' said Professor Landon.

'Its venom has some particularly nasty properties. An anticoagulant makes you bleed to death and a vasculo-toxin gives you a heart attack.' Rattlesnakes, including Georgia's eastern diamond back variety, bear the same deadly arsenal.

In Australia the tiger snake, the brown snake and the taipan are the deadliest and responsible for 18 human deaths a year. Professor Landon has developed a first-aid antivenin kit for hikers, the military and farmers in the outback.

'Currently, antivenin has to be administered intravenously, but we are working on an antidote that can be injected into the muscle. That means just sticking the needle into your leg or arm as soon as you are bitten.'

Another development involves those stars of Australian toilet jokes and beer commercials, the deadly redback and funnel-web spiders. These are also about to have their lethal poisons tackled by the serum from the humble sheep. Australia could take over from Wales as the leading centre of antivenin production. Professor Landon said: 'If this takes off we might need to get into serious numbers of sheep.'

(Photograph omitted)