The alert is part of the study “Resistance to anticoagulant rodenticides challenges pest control efforts in Portugal”, authored by Ana Santos, a graduate in Biology and Master in Evolutionary and Developmental Biology.

PhD student at the Faculty of Sciences of the University of Lisbon, Ana Santos is developing her thesis focusing on the difficulties in controlling pests of rats and domestic mice due to resistance to the biocides used. The scientific article has now been published.

Speaking to Lusa, Ana Santos explained that mutations are normal and spontaneous in animals, but added that "they are small changes that do not change the normal function of proteins but can alter some mechanisms, in this case, resistance to compounds” which are the anticoagulant rodenticides, rat poisons.

Thus, when the poison is used to control pests, there are rats that will resist, and the more the compound is used, the more resistant the population becomes, because the rats that have the mutations will survive and those that do not have them will die, in a mechanism identical to that of antibiotics and resistant bacteria.

Ana Santos told Lusa that these genetic mutations were already known but had not yet been studied in Portugal.

“We didn’t know if the mice had the mutations”, she highlighted, explaining that the studies showed, for example, that on some islands in the Azores, all the animals studied were already resistant to anticoagulant rodenticides, while on the island of S. Miguel, of the 40 samples studied, only five had the mutation that gave them resistance.

The expert considers that the results may be worrying, because the percentage of resistant individuals is very high, and argues that the country should be mapped and based on this, the rodenticide should be chosen depending on whether there is resistance or not.