Dirofilaria immitis and D. repens, the agents of human pulmonary and subcutaneous dirofilariasis respectively, may coexist in areas of southern Europe. They are the only filarial parasites in Europe occasionally transmitted to man. The usual hosts of these nematodes are domestic and wild carnivores. Dogs are the most common host though cats, foxes (Vulpes vulpes) and wolves among other carnivores may also serve as hosts. In their canine and feline hosts these parasites are commonly known as canine heartworm. The vectors include mosquito species in the genera Aedes, Anopheles and Culex.

Canine subcutaneous and cardiopulmonary dirofilarioses are widely extended through the southern countries of the continent and are less frequent or completely absent toward the north. Italy, Spain, France, Portugal and Greece are the countries where epidemiological studies have demonstrated the presence of both D. immitis and D. repens in domestic (dogs and cats) and wild carnivores (mainly foxes). Italy is the European country where Dirofilaria species are most frequently found. The northern limit in which these two species have been reported, is the area of Cherbourg, France (Doby et al., 1986). There is clear evidence that Dirofilaria infections are spreading in animal populations (Rossi et al., 1996). Mosquito density and large numbers of microfilaraemic dogs are the most important risk factors for the transmission of the infection to humans. Dirofilaria repens infection is the most frequent and widespread dirofilariasis species.