Dirofilaria repens

Dirofilaria repens is a filarial nematode that affects dogs and other carnivores such as cats, wolves, coyotes, foxes, and sea lions, as well as muskrats. It is transmitted by mosquitoes. Although humans may become infected as aberrant hosts, the worms fail to reach adulthood while infecting a human body. It most often found in the Mediterranean region, sub-Saharan Africa, and Eastern Europe. Italy bears the highest burden of European dirofilariasis cases in humans: (66%), followed by France (22%), Greece (8%), and Spain (4%). In Europe, the parasite has spread as far north as Estonia.. The lifecycle of D. repens consists of five larval stages in a vertebral host and an arthropod (mosquito) intermediate host and vector. In the first stage, mated adult female worms produce thousands of microfilariae (larvae) into the circulation daily, which are ingested by mosquitoes in a blood meal. Larvae develop into infective larvae within the mosquito over the next 10–16 days, depending on environmental conditions, before being reintroduced back into a new host. Microfilariae undergo secondary developmental changes in the insect. For the final two stages of development, third-stage larvae are inoculated back into a vertebral host during an act of feeding. The adults of D. repens reside in the subcutaneous tissues of dogs and cats, where they mature in 6–7 months. Adult worms are 1–2 mm in diameter (females are 25–30 cm in length, the males being shorter).