Nutrias and muskrats as bioindicators for the presence of Echinococcus multilocularis in new endemic areas.

Nutrias (Myocastor coypus) and muskrats (Ondatra zibethicus) are large invasive semi-aquatic or aquatic rodents, naturalized throughout Europe. They are regarded as pests, and can be infected with several pathogens and parasites transmissible to wildlife, livestock, pets and humans. As a rule, in Europe the life cycle of the cestode Echinococcus multilocularis involves red foxes (Vulpes vulpes) as main definitive hosts and common voles as intermediate hosts. The suitability of nutrias and muskrats as intermediate hosts has already been described. Here, we investigate the occurrence of E. multilocularis in the context of a wide-scale health study on nutrias and muskrats in 12 "départements" in the western part of France. During the sampling period, a total of 817 aquatic rodents were trapped in five rivers or ponds in each "départements". During post-mortem examinations, lesions were observed on the livers of 21 nutrias and 104 muskrats, and analyzed by PCR and sequencing of the mitochondrial cox1 gene for specific identification. Several non-zoonotic parasites were identified: Taenia taeniaformis, Taenia mustelae, Taenia polyacantha and Taenia martis. Four livers from 2 nutrias and 2 muskrats exhibited E. multilocularis infection. One of the muskrats was infected with fertile E. multilocularis lesions. The 4 animals came from 3 French "départements" where foxes have recently been found to be infected by E. multilocularis. These results lead us to consider nutrias and muskrats as relevant bioindicators for the presence of E. multilocularis in this environment. Our results also suggest that, when listed as pests and targeted by large trapping campaigns, nutrias and muskrats could be used to detect the presence of E. multilocularis in areas considered free of this parasite.