Outside the areas where exotic human filariasis are rife, more than 27 species of filaria usually parasitic on domestic or wild animals can be accidentally transmitted to humans [1]. Dirofilaria are nemathelminths belonging to the Onchocercidae family. Two subgenus have been identified: Dirofilaria, including D. immitis; and Nochtiella, five species of which may be responsible for human infections [2]. D. repens, the most common species in Europe, D. tenuis, D. ursi, D. subdermata and D. striata in America. Only two species can infest man: essentially the subgenus Nochtiella represented by D. repens and also the subgenus Dirofilaria represented by D. immitis. The latter is a cosmopolitan wireframe. It is the agent of human pulmonary dirofilariasis and exceptionally other visceral localizations. As for D. repens, widespread in Asia, Europe and Africa and particularly around the Mediterranean basin. It is the cause of subcutaneous or conjunctival damage, more rarely genital, peritoneal, and even pulmonary [1, 3]. Our observation describes a benign nematodosis, subcutaneous heartworm disease caused by D.repens. The definitive host is a carnivorous mammal (especially dogs or cats). The intermediate and vector host is a Diptera of the Culicidae family, belonging mainly to the genus Aedes. However, the genera Anopheles and Culex may be involved. This vector transmits the microfilariae in the blood of the animal during an infesting meal. These develop in the muscles of the insect to give infesting larvae which migrate to the tubes to be transmitted by a new bite to the animal but also accidentally to humans. Heartworm is generally immature in humans which is considered a parasitic dead-ends. Human infections with D.repens are increasingly reported in Europe and in countries around the Mediterranean area, with a major focus in Italy [4]. In Tunisia, there have been 16 cases since 1990, including eight with subcutaneous localization [5, 6].Other cases have been reported with different location (scrotal, ocular, axillary, breast, paraombilical) [7, 8]. The patients came from different regions of our country. Around the Mediterranean basin, canine reservoirs and vectors are abundant. But, human cases of heartworm disease are rare. It is therefore possible that this pathology is underestimated due to a non-specific and benign symptomatology [9]. Clinically, subcutaneous heartworm disease is manifested in most cases by a little or no painful nodule, sometimes associated with local inflammatory signs. Incubation does not exceed 6 months (1 month for our patient) followed by the appearance of a subcutaneous nodule of 1 to 4 cm, little or not painful, sometimes preceded by a sensation of painful edema [10]. This nodule is most often unique. The bite usually goes unnoticed; moreover, it is only rarely reported. The diagnosis is very often of accidental discovery.

Pathological examination reveals sections of D.repens generally in the form of adult female worms, generally immature, as was described in our patient. Morphological analysis of the parasitic sections made it possible to conclude on the diagnosis of dirofilariasis caused by D.repens on the diameter of the nematode (sections from 300 to 600 μm in the female and from 250 to 450 μm in the male), the presence of ten papillae cephalic on the anterior extremity, the well-developed muscular structure of the polymyar type, the internal organs that do not fill the cavity and the presence of a multilamellar cuticle, surmounted by parallel longitudinal ridges and regularly spaced 3 at 4 μm, or about 25 per quadrant [11]. The diagnosis is rarely made by direct examination of an adult worm. It is essentially histological, brought to pathological examination of the resected nodule by revealing a section of the parasite surrounded by a polymorphic inflammatory infiltrate including lymphocytes, plasma cells, histiocytes and eosinophils, which constitute a granuloma [2, 12, 13]. Serological diagnosis of the D. repens and D. immitis subgenera may be possible but remains insensitive and unspecific [12]. Biological diagnosis makes it possible to detect the parasite in humans before resection and could help in species identification. DNA analysis by PCR is considered the gold standard, even when small or altered larval fragments are used [14].

These new methods can be of interest for the diagnosis of visceral forms inaccessible to surgery. These methods are not common practice and they are unavailable in Tunisia. The diagnosis of subcutaneous heartworm is based on the morphological study of the filaria. Treatment is based on surgical removal of the nodule [12, 15]. In our observation, the diagnosis was histological by the demonstration of a section of a nematode following surgical exeresis. The spontaneous evolution was favorable.