Mutant 'super rats' that cannot be killed by regular poison are running rampage across Britain, warn experts.
The rodents are believed to be quickly spreading after researchers found some in Sussex, following finds in Kent and the west country.
Health authorities are reportedly concerned as rats carry lots of diseases, including potentially deadly bacteria.
Dr Dougie Clarke, of the University of Huddersfield, told the Daily Star: "Poisons such as the ones you buy in B&Q are not effective against them, nor are those used by pest control experts.
"There are obviously health concerns and worries about the bacteria they carry, such as salmonella.
"They carry a lot of diseases, including Weil's, which has been linked to deaths. They also chew on electrical cables."
Sir Steve Redgrave's former rowing partner, Olympic champion Andy Holmes, died of Weil's disease in 2010 after an event in Lincolnshire.
The British Pest Control Association's Richard Moseley told the Metro that these rat numbers are "expanding", saying: "Normal rats are being killed off by poison, so these resistant species are taking their place – it's only natural that their numbers are expanding.
"They eat poison like feed; you might as well be leaving out grain for them."
The amount of poison these rats have been eating has also led to fears that if family pets bite them, they could die from the effects.
It is believed these poison-resistant rats could have developed because of a naturally occurring mutation of genes. Although they have been around for about 50 years, it is thought their rate of breeding now poses a "public health risk".
Researcher Dr Dougie Clarke told Metro: "The only solution is stronger poisons. There are concerns about poisoning of secondary animals and birds but, if it's carefully controlled, it can be kept to an absolute minimum."
Mr Moseley agreed, adding: "Rats carry and spread diseases, so if their populations are left unchecked there can be a big public health risk."
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