Dirofilaria repens transmission in southeastern Finland

Abstract

Background: The spread of vector-borne diseases to new regions has become a global threat due to climate change, increasing traffic, and movement of people and animals. Dirofilaria repens, the canine subcutaneous filarioid nematode, has expanded its distribution range northward during the last decades. The northernmost European locations, where the parasite life-cycle has been confirmed, are Estonia and the Novgorod Region in Russia.

Results: Herein, we describe an autochthonous D. repens infection in a Finnish woman. We also present two cases of D. repens infection in imported dogs indicating the life-cycle in the Russian Vyborg and St Petersburg areas, close to the Finnish border.

Conclusions: The most obvious limiting factor of the northern distribution of D. repens is the summer temperature, due to the temperature-dependent development of larvae in vectors. With continuing climate change, further spread of D. repens in Fennoscandia can be expected.

Keywords: Autochthonous infection; Climate change; Dirofilariosis; Vector-borne nematodes; Zoonosis.

Fig. 1

The northernmost Dirofilaria repens infections found reported. See text for further information of the reports. 1, Hamina (61°N, 27°E); 2, Vyborg (61°N, 20°E); 3, St Petersburg (60°N, 30°E); 4, Tartu (58°N, 27°E); 5, Novgorod Oblast (58°N, 33°E); 6, Arkhangelsk (65°N, 41°E); 7, Yakutsk (62°N, 130°E)

Fig. 2

Histopathology as seen in the subcutaneous lesion (a and b) and microfilaria found in the blood smear (c) from the human patient, a 70 year-old female. A diffuse dermal inflammatory infiltrate composed of eosinophilic granulocytes and histiocytes surrounding an adult female filarioid nematode can be observed in (a). The area in the rectangle is enlarged in (b). A cuticle with evenly spaced external longitudinal cuticular ridges, a musculature of coelomyarian type, a small intestine and a paired uterus filled with microfilariae were considered typical of Dirofilaria spp. Haematoxylin-eosin stained histological section. A microfilaria possessing three nuclei in a large cephalic space (arrow) can be observed in (c). Abbreviations: cut, cuticle; mus, musculature; in, intestine; ut, uterus; mf, microfilariae. Scale-bars: a, 100 μm; b, 50 μm