Autochthonous human Dirofilaria repens infection in Latvia: a case report supported by retrospective canine surveillance data

Dirofilaria repens, a mosquito-borne zoonotic nematode of dogs and other carnivores, has undergone marked geographic expansion across Europe in recent decades, spreading from its Mediterranean origin into southern, eastern, and Baltic Europe, likely driven by climate warming and dog movement. We describe a documented case of D. repens infection in Latvia, interpreted alongside retrospective canine surveillance data. A 59-year-old man with no history of international travel presented with a persistent painful swelling near the lacrimal sac unresponsive to empirical antimicrobial and anti-inflammatory therapy. Surgical excision revealed a live nematode within a fibrous pseudocyst; based on characteristic morphology, the parasite was presumptively identified as D. repens. Histopathological and immunohistochemical examination demonstrated a chronic inflammatory response with macrophage-rich granulation tissue, lymphocytic infiltration, angiogenesis, and collagen deposition. Routine modified Knott test results from 1,250 clinically suspected dogs tested between 2021 and 2024 were retrospectively analysed; D. repens infection was detected in 12.0% of dogs, with no significant temporal or seasonal variation, indicating sustained parasite circulation in the canine population. These findings support local human transmission of D. repens in Latvia. Despite being the principal cause of human dirofilariasis in Europe, D. repens remains less studied than Dirofilaria immitis, and limited emphasis on zoonotic parasitic infections in medical education continues to hinder recognition. Greater clinical awareness, veterinary-medical collaboration, and a One Health approach are essential to improve recognition, surveillance, and control of this emerging zoonosis.