A SCIENTIFIC investigation has been launched into the mutant Hampshire rats that have become almost impossible to kill.

A team of scientists is focusing on a new breed of “super-rats” that have developed a resistance to traditional poisons.

As first reported by the Daily Echo 18 months ago, DNA tests on tails collected from rats across the county confirmed the presence of a mutant gene that helped protect the disease-carrying rodent.

Local pest controllers are having to use more powerful poisons to control the rat population north of Winchester, but say it’s only a matter of time before the creatures arrive in Southampton.

A £30,000 study into the phenomenon was launched this month and is focusing on seven areas across the UK where there have been reports of toxin-resistant rats.

As well as Hampshire, the other hot spots include Avon, East Anglia, the south-east, mid-Wales, Yorkshire and the Scottish Borders.

Rodent specialist Professor Rob Smith said 60 local authorities were taking part in the year-long survey that will analyse up to 1,000 rats.

Samples will be taken every 10km, from Southampton in the south to Oxford in the north, and from Guildford in the east to Salisbury in the west.

Council pest control teams will be asked to remove the tips of the rat’s tails and dispatch them to the University of Huddersfield for testing.

“It will be the first time that we will have an unbiased idea of the problem. One of our areas of great interest will be Hampshire,” Professor Smith said.

“Hampshire was the first place where there was a resistance, and the problem has built up ever since then.”

The super-rats are stronger thanks to an ability to resist the usual kind of anticoagulant poisons laid out to kill off the pests by exterminators.

With extended exposure to poison, resistant rats continue to breed while others die off, leaving a resistant population.

In a classic “survival of the fittest” scenario, individual rats do not develop resistance – they are either born with it or without it.

Professor Smith hopes the Huddersfield Rodent Resistant Project will uncover how far the mutation has spread and convince the Government to take the problem seriously.

“The intention is that the relevant Government departments will be asked what they are going to do about resistance once the extent of the problem is properly established,” he explained.

“One of the big worries with rats is the disease they spread, and resistant rats should be of concern to the Department of Health as well as Defra.”

One man who doesn’t need convincing is Sean Whelan, from Southampton-based Whelan Pest Control. He has seen the local rat population explode in recent years.

“North of Winchester, and in fact now in Winchester, the bait we are using is stronger than the bait we are using in Southampton,” he said.

“It’s strong stuff, we are talking about something that could harm humans. It’s only a matter of time before the rats in Southampton also show resistance to the bait.”

Latest figures show that the number of rat-related call-outs by Southampton City Council’s public health team has actually fallen over the past three years.

In the 2007-8 financial year the team received 995 rat reports, compared with 681 in 2008-9 and 768 in 2009-10. However, council rat catcher Justin Crow believes the statistics hide a worrying truth.

He said the rat population was continuing to flourish, but residents were either trying to deal with the potentially dangerous threat themselves or ignoring it altogether.

“We are seeing increases in rats in Southampton. There is no doubt about that, but we are seeing the number of people calling us go down,” the deputy supervisor said.

“Whether that is because of the economic climate or people are becoming more accepting of rats in their community, we are not sure. But there has definitely been a change of attitude.

“There is a great number of people who think they are just furry little creatures and don’t realise they are doing any harm.”

Rats carry and transmit a number of diseases that affect both humans and farm animals, including diseases as serious as salmonella and leptospirosis.

Both Mr Whelan and Mr Crow advised homeowners against trying to kill rats with bait bought for as little as £5 from DIY stores.

The experts said they were often not strong often to kill the rodent humanely and were not a long-term solution to infestations.

“People expect miracles, but if you don’t know what you are doing you put your own health at risk,” Mr Crow added.