Rampaging squirrels to go on the pill

A CONTRACEPTIVE vaccine for grey squirrels is being developed as a humane alternative to traditional methods of population control such as shooting and poison.

The grey squirrel is widely blamed for the decline of Britain's native red squirrel, which conservationists fear could soon become extinct. There are 2.5m grey squirrels in the UK and just 161,000 red, according to the Joint Nature Conservation Committee review of British mammals.

Professor Harry Moore, of the University of Sheffield's molecular biology and bio-technology department, has spent the past five years developing the "harmless" squirrel contraceptive. The project is jointly funded by the Ministry of Agriculture and the Forestry Committee.

The protein vaccine, which will be developed orally through a bait, is targeted at the female squirrel. Professor Moore has managed to identify the sperm receptor on the female's egg. The protein vaccine, which creates antibodies, then binds to this receptor and renders the egg infertile. "We have known for 50 years that certain antibodies make humans infertile so we have adapted it for squirrels," he said. "We can target this vaccine to just one species because fertilisation is very specific. It would not affect other animals. This avoids the ethical problems associated with poisoning or shooting, and it's far more effective."

Eighty per cent of the female population must eat the bait to ensure the vaccine is successful. The effects are not permanent, so the bait would have to be administered once a season to keep populations low.

Harry Pepper, a wildlife forester with the Forestry Commission, is keen that an effective means of controlling squirrels may soon be available: "Squirrels strip the bark from trees and kill them. With other methods of control becoming less acceptable to the public, the commission wishes to find a more acceptable means. The development of the contraceptive vaccine is an alternative that would address these issues."

In Australia, a similar technique has been used to limit the number of mice and in Africa a comparable vaccine is used to maintain a stable elephant population. In the long run scientists hope the discovery of a contraceptive based on naturally produced antibodies could be used with humans.

"This would be the next generation in human contraception as it would not involve the use of potentially damaging hormones," said Professor Moore.

However, safe contraception for squirrels will be available far sooner. If further laboratory tests are successful the vaccine will be on the market within the next five years.