[Preliminary report on the demonstration of resistance to coumafene in Rattus rattus in Marseilles]

An abnormal proliferation of Rattus rattus in an important food-products warehouse in Marseille's periportuary zone has been recorded in spite of preventative measures put in place and aimed at testing these rodents resistance to basic anticoagulants, especially to coumafene. The laboratory experiments on animals taken from the invaded area have enabled us to prove for the first time on metropolitan ground a Rattus rattus resistance to coumafene. The colony of rodents responsible is giving proof of its resistance in already large proportions, since the survival beyond 10 days of treatment is established in 74% of the tested subjects, whereas 30% of them survive treatments prolonged by 4 to 10 weeks. The recorded results allow us to confirm the variable degrees of the state of resistance which appear to be developed locally, the origin of which cannot be defined. Taking into account the size of the affected zone and the numerous food-products storage establishments found there and usually infected with Rattus rattus, one is forced to fear a rapid progress of the territorial resistance. It is therefore opportune to take the necessary measures to destroy the resistant colony on the spot, to follow the ultimate progress in the area and to follow up in the laboratory the methods of evaluation of the efficiency of new rodenticides.