The first sign of resistance seen by practitioners is often the failure of control practices which are normally effective. However, there are many possible reasons for such failure and careful consideration of all possible explanations is first necessary (Prepare a rodent control and determine your individual resistance risk level, see also Checklist for users). If, after consideration, other explanations are ruled out, an important next step is the collection of tissue samples from the suspected resistant infestation and confirmation, using DNA-sequencing, of the presence of a resistance mutation (LINK zu Punkt 1: Testing for resistance, und Punkt 5 Laboratories). This will permit resistance specialists to understand the nature of resistance present and to develop and promote effective strategies to remove resistant infestations.
When resistance is confirmed using DNA-sequencing or PCR, it is essential to pass this information to local resistance specialists and/or to a rodenticide resistance working group (see also Laboratories), so that an up-to-date record of the distribution of resistance can be kept. Those who apply anticoagulants in areas where resistance is known to occur should always make the assumption that resistance is present at treated sites unless there is positive proof to the contrary. This precautionary measure will tend to restrict the spread of resistance, rather than promote it. Of course, confirmation of the presence or absence of resistance on a site-by-site basis using DNA-sequencing is extremely helpful.