Alaria alata mesocercariae in raccoons (Procyon lotor) in Germany

Alaria alata is a trematode of carnivores from Europe. The mesocercarial stage was recently identified in wild boar meat from Europe. Previous histopathologic studies showed the presence of unidentified parasitic cysts within the tongues of raccoons from northern Germany. For identification of the parasite species, tissue samples of 105 raccoons originating from a National Park in northern Germany and from Berlin metropolitan area were collected. Histological examination of cryotome sections of frozen as well as paraffin-embedded tongues were used to identify parasite cysts. These were located in the connective and adipose tissue and in close proximity to small arterioles, suggesting a hematogenous spread of the parasite. Often, cysts were surrounded with mild infiltration by inflammatory cells. Additionally, mesocercariae were isolated from defrosted tongue samples of 11 raccoons. Molecular-biology assays confirmed the parasite species as A. alata. Except for one positive raccoon from Berlin City, all other positive raccoons originated from the sylvan Müritz National park, indicating an abundance of intermediate hosts in this area. Our results show that raccoons can act as paratenic hosts for A. alata and extend the broad host range of this parasite to a species introduced into Germany.