Rats and Mice are well known for spreading diseases such as plague, weils disease and cryptospridiosis but this article focuses on their gnawing behaviour, why they do it and what risks it presents to public health.
Rodents are characterised by their teeth. They have a pair of incisor teeth in the upper and lower jaws, separated from the molars by a large gap (diastema).
The incisors do not stop growing. This means that the animals are forced to gnaw steadily in order to wear them down.
This picture shows a skull from a rodent specimen who’s incisors hadn’t worn correctly and had become overgrown.
The incisors are curved inwards and have an extremely hard anterior coating,The enamel of rat incisors is hard, harder than iron, platinum and copper.
The softer inside layer is worn down much more rapidly than the hard, outer layer.This means that the teeth are continually kept sharp, enabling them to damage even materials such as masonry and electric cables.
Rats are believed to have caused a massive blaze that destroyed three coaches and three minibuses at a coach company headquarters in Southampton in December of 2012.
The rat has small flaps of cheek tissue on either side of the inside of the mouth that close behind the incisors, protruding into the gap between the incisors and the molars (the diastema) These flaps are believed to form a plug that keeps unwanted debris from entering the mouth,a rat does not have to swallow or even taste what it chews,allowing them to gnaw away with impunity.
Here, we have the skull of Rattus norwegicus, The Brown rat, the incisors and diastema are clearly visible.
Next, A Grey Squirrel, Sciurus Carolinensis.
Here we see the very clear teethmarks of a brown rat on a piece of electrical cable.
this is an old bait tray, that would have held rodenticides once, it would appear that the local rodent population not only consumed the bait but found themselves partial to the plastic tray themselves.
If you suspect that you have rodents in your property, The safest and most efficient way to deal with them is to contact a professional pest control company, such as Cavalry Pest Solutions.
‘MUTANT SUPER RATS’
If you’ve recently seen a headline similar to the above, Don’t be unduly alarmed, the fact that you’re reading this blog means that you’re about to find out just what the Issue is and what is being done about it!
Rodenticides in The U.K
With the exception of one (Alphachloralose), All rodenticides licensed to control rats and mice in the u.k are anticoagulants, that is they interfere with the clotting process of blood, this means that death is normally due to internal haemorrhage.
The most famous of these compounds is ‘warfarin’ (Wisconsin alumni research foundation + Coumarin) commonly used to treat thrombosis and similar conditions in humans.
Warfarin, along with Chlorophacinone and Coumatetralyl are known as first generation anticoagulant rodenticides (FGARs)
Resistance to the first generation of anticoagulant rodenticides was discovered in rats (R. norvegicus and R. rattus) and mice (Mus musculus domesticus) in the United Kingdom around 1960, approximately 10 years after the first use of anticoagulant rodenticides.
Similar resistance has now been reported in many countries across the globe.
The second-generation anticoagulant rodenticides (SGARs) were specifically developed to overcome resistance, but resistance to several of these more potent analogs has now been detected.
Continued use of anticoagulant rodenticides against these populations of resistant rats is likely to maintain the selection pressure toward higher prevalence and degrees of resistance.
Second Generation Anticoagualnt Rodenticides (SGARS)
The 2 SGARS which are the main focus of the problem are Difenacoum and Bromadiolone, both are ‘multi-feed’ rodenticides (That is, a rodent usually needs to feed on them a number of times before the active ingredient takes effect) and both are available to the professional sector AND the general public. Any rodenticide product that you see in the high street, supermarket etc will be one of these two.
There are other 3 SGARS available, which have greater levels of toxicity than Difenacoum and Bromadiolone, Brodifacoum, Flocoumafen and Difethialone. There is no known resistance to products containing these actives. They are technically ‘multi-feed’ rodenticides but Rats & Mice frequently eat enough in one feed to have a lethal effect, This has led to some people referring to them as ‘single-feed’
At present it is illegal to use any of these 3 outdoors.
Resistance in Rats and Amateur Use
Although genetic resistance occurs naturally in Rats and resistant organisms are simply following the rules of evolution; the best-adapted individuals survive and pass their resistance on to their offspring, Incorrect usage of rodenticides can actively increase resistance.
The availability of these products to the general public is believed to have contributed to the spread of resistance throughout the U.K.
Many professionals feel that rodenticides shouldn’t be available for use by untrained members of the public, Pest Controllers have to produce evidence of qualifications and training to suppliers when ordering products.
Another problem is that amateur users are less likely to interpret safety instructions on correctly and are less likely to understand how to use the products to best effect.
Personally, as well as the Issues already mentioned I feel that the sale of products to amateur users devalues The Industry and disregards our role in contributing to safeguarding public health.
Obviously, SGARs are not selective and precautions need to be taken to minimise the risk to non-target species and it is when this does happen, for example if rodenticide is eaten by a vole that in turn is caught and eaten by a kestrel that the rodenticides enter the food chain and the problem of ‘secondary poisoning’ occurs.
The Campaign for responsible rodenticide use (CRRU) (Cavalry Pest Solutions are registered CRRU Supporters) has produced the CRRU Code, a 7 point strategy to minimise risks to the environment and non-target species. The CRRU also developed ‘Wildlife Aware’ Accreditation in conjunction with BASIS-PROMPT. (At Present, The only Pest Controller registered in the Wigan Borough as being ‘Wildlife’ Aware Accredited is Elliot Lowe, Senior Pest Control Officer at Cavalry Pest Solutions.)
Last year,The Health & Safety Executive invited a number of stakeholders from across the country, representing pest control, gamekeepers, environmental organisations to a meeting to discuss the way forward for the use of SGARs in The U.K. (Cavalry Pest Solutions were one of the stakeholders invited to the meeting)
Proposals have suggested that a Stewardship Scheme headed by the CRRU is the preferred option, further meetings with stakeholders are to be held next year.