EN
Dirofilariasis caused by Dirofilaria repens nematodes is a parasitosis occurring in dogs, cats and wild carnivores in southern Europe. In Poland it was found for the first time in 2009 in dogs in the Mazovian Province. The nematodes of that species are mostly found in nodules located in the subcutaneous connective tissue or intramuscular connective tissue of the trunk and legs. The aim of this paper was to describe a case D. repens nematode located in a dog’s testicular parenchyma. An eight-year-old German shepherd dog was found to have an enlarged left testis. After castration, during the extraction of a sample from the removed testis for histopathological examination, an oval, three-centimeter-wide cyst filled with clear liquid was found. Inside the cyst, a long, spirally rolled white nematode was detected - a mature female belonging to the D. repens species. In the dog’s blood, microfilariae of that parasite were also identified. The histopathological examination of the cyst wall showed the presence of a tumor composed of Leydig cells of a cyst-vascular type. The dog came from the Mazovian Province and had never been away, which suggests that this was a native invasion. This is the first case of D. repens in an intra-testicular location in a dog.