Subcutaneous/ocular dirofilariasis caused by Dirofilaria repens is a vector-borne zoonosis affecting dogs and humans in the Old World. While dogs are the natural reservoirs, humans can be accidentally infected when they are bitten by mosquitoes that previously fed on infected dogs. Human subcutaneous/ocular dirofilariasis is characterized by the appearance of benign subcutaneous nodules that can be mistaken by cutaneous carcinomas and by the location of immature or fully developed worms free or encapsulated in the ocular area.1 Most cases have been reported in Europe, where a geographical spreading from the Southern endemic countries to previously non-endemic central and Northern countries has been observed in the last ten years. These spreading is attributed both to global warming and the lack of preventive measures in canine populations, given the usually asymptomatic character of this parasitosis in the animal reservoirs.2 To the present, in Spain D. repens has been detected exclusively in the canine populations of the Mediterranean coastal provinces and Balearic Islands and only 8 human cases have been reported in the same areas.3 In the present work a clinical case of human subconjunctival dirofilariasis, reported in an area of Northwestern Spain where canine infections by D. repens have not been previously observed, is described in a patient with Multiple Endocrine Neoplasia type 2 (MEN2).
Case presentationA 39-year-old man attends medical consultation in the Ophthalmology Service of the Healthcare Complex of Zamora (Northwestern Spain) for the follow-up of a chronic keratoconjunctivitis related to MEN2. During consultation the patient refers only a slight conjunctival irritation. Ophthalmological exploration evidenced hyperemia and the presence of a subconjunctival nodule in each eye, compatible with filarial parasites. Surgical removal of the 2 worms with topical anesthesia was difficult as a consequence of the adherence of the parasites to the conjunctiva and their friability. Several fragments of both worms with different sizes were obtained (Fig. 1A). Parasitological identification was not possible on the basis of the morphology and morphometry in our laboratory because the nematode was significantly damaged. It was sent to Laboratory of Parasitology of the University of Salamanca for identification by polymerase chain reaction (PCR) technique.
(A) One of the fragments of the worms removed from the subconjunctival tissue of the patient. (B) Multiplex PCR amplification of the DNA extracted from the worms removed from the patient. Lane 1: negative control; lane 2: D. repens positive control; lanes 3 and 4: samples obtained from the worms surgically removed from the patient; M: molecular marker, 100–1000pb.
DNA was extracted, amplified by PCR4 and visualized in agarose gel electrophoresis (Fig. 1B) showing a pattern of bands compatible with D. repens. This confirms that both subconjunctival nodules were due to a dirofilariasis caused by this species. Subsequent exploration did not evidenced residues of the parasites. Blood tests showed a number of eosinophils within normal range (0.1×103/mm3) and characteristic alterations of MEN: high calcitonin (11,220ng/L), parathormone (92ng/L) and cromogranine A (>2445ng/L) levels. The patient has not farming, hunting or fishing activities and he had not traveled outside the residence area in the in the last years and ever has had dogs. He lives in a humid area with 3 rivers and extensive irrigated crops, typical environmental characteristics of endemic areas of dirofilariasis in Spain.5
DiscussionTo our knowledge this is the first time that conjunctival dirofilariasis is described in a patient suffering from MEN. This is characterized by the appearance of multiple malignant or benign tumors in endocrine gland. The basic treatment of this condition is the surgical removal of the tumors associated, when necessary, to pharmacological treatment of the hormonal hypersecretion and/or substitutive hormonal therapy.6 Nevertheless, not immunosuppressive therapy that could facilitate the establishment of pathogens is employed and consequently we cannot establish the relationship of cause/effect between MEN syndrome and dirofilariasis. However, MEN especially variant 2, is associated with chronic keratoconjunctivitis. Probably this fact has been a local risk factor to make it susceptible to infection. Human dirofilariasis caused by D. repens presents as subcutaneous nodules/subconjunctival location. Thus it is necessary to consider this condition in the differential diagnosis of other pathological processes affecting subcutaneous or subconjunctival tissues. Canine and human subcutaneous/ocular dirofilariasis is considered currently an emergent parasitosis in Europe, attributing this fact to the introduction of infected asymptomatic dogs from Southern endemic areas into non endemic central and Northern areas of the continent in which adequate environmental conditions for the transmission have appeared as a consequence of global warming.2 In Spain human and animal dirofilariasis caused by D. repens has been reported exclusively in the Eastern Mediterranean area3. The variety and abundance of vector species and the number of larvae that complete the development are factors that determine the efficiency of transmission in this area. Although in this patient there was no epidemiological suspicion, since there are no previous cases described in the area, it must be considered that there is a risk of infection if there are infected dogs in the environment. The fact that this case has been detected in the West of the Iberian Peninsula suggests that, like in the rest of Europe, D. repens could be spreading stealthily in canine populations living in other parts of Spain and consequently becoming a risk factor for the human populations of these areas. In conclusion, this case should take attention about the possibility to find cases of subcutaneous/ocular dirofilariasis associated to MEN and the spreading of D. repens into previously non-endemic areas in Spain.
Unfortunately, we do not have images of the nodules prior to excision, which would have allowed a differential diagnosis, however the initial suspicion was ocular dirofilariasis since the worm was appreciated with the naked eye.
