Histological and molecular confirmation of the fourth human case caused by Dirofilaria repens in a new endemic region of Slovakia

Dirofilariosis is considered to be the arthropod vector-borne disease with the fastest spread in Europe. Slovakia belongs to new endemic regions for canine and human infections. This paper reports the fourth human case, where diagnosis was confirmed using computed tomography (CT), histological and molecular examinations - for the first time in this endemic region. The epidemiological history of this case indicated the autochthonous origin, and infection manifested by intense swelling in the periocular region, where a subcutaneous nodule was localized. Microscopic analysis of cross-sections of the surgically removed nodule confirmed the presence of a single male worm of Dirofilaria repens, indicated by the external cuticular ridges, the robust muscle cells and a single male sex organ seen as one tube beside the intestine. Considering that the worm morphology was partially damaged, molecular study was performed using DNA isolated from formalin-fixed and paraffin-embedded tissue sections of the worm. In polymerase chain reactions (PCR) a set of primers specific for D. repens DNA for the CO1-encoding gene amplified the expected 246 bp product using a high concentration of DNA template. Our diagnostic approach, involving molecular techniques, showed that identification of D. repens from excised tissues is possible even when the morphology of the worm and DNA are damaged during tissue processing. It is expected that the spread of this disease will continue due to climatic changes in central Europe. This warrants higher awareness among clinicians, who will initially be approached by patients, and better co-operation with parasitologists in newly endemic countries.