Peri - Orbital human dirofilariosis: A pitfall for experimental ELISA

The dog nematodes Dirofilaria immitis (D. immitis) and D. repens, well known as zoonotic agents, can infect humans in whom they usually produce abortive infections or immature worms. Dirofilarioses, asymptomatic in most patients and suspected only when the worm reaches surface locations or imaging detects coin lesions, are under-diagnosed because both physicians do not consider this aetiology and the human immune response blocks the worm development at early larval stages, difficult to be located. The identification of the infecting species is based on morphological/genetical study of surgically removed specimens. Serology should be an alternative to the invasive methods, also useful to detect hidden infections; nevertheless, at present, there are no commercial kits to specifically diagnose human dirofilarioses. The aim of the study was to test the sensitivity of experimental serological assays in a case of peri-ocular dirofilariosis caused by D. repens, which had been identified by morphology and molecular methods (PCR). Serological investigations included two serum samples, one before surgery intervention and the other one six months after extirpating the worm. Specific antibodies against both somatic/metabolic antigens of D. repens and D. immitis adult specimens, and against antigens of the filarial endosymbionts belonging to the genus Wolbachia were evaluated. Sera were submitted to experimental enzyme immunoassay (ELISA) protocols, and to an ELISA commercial kit available to diagnose human tropical filarioses. Diagnostic significant titres of specific antibodies by any applied test were not found. As suspected, peri-ocular case of human infection due to D. repens proved a pitfall for serology, even if immunodiagnostic tests are designed with a wide range of antigens that are released by the worm, starting from its penetration in the human host.