Pitfalls and difficulties in histological diagnosis of human dirofilariasis due to Dirofilaria (Nochtiella) repens

The authors have conducted a histologic study of over 90 cases of Dirofilar ia infection in man due to Dirofilaria repens, the most extensive study of its kind in the would. On the basis of their findings, they illustrate the diagnostic difficulties that may arise when regreessive phenomena I ender t he parasite's morphologic characteristics largely or completely unrecogniza ble. These phenomena are due to the death of the filaria inside the inflamm atory nodule weeks ol months prior to surgical removal, and to the conseque nt invasion of inflammatory cells. They start at the nenatode's natural ori fices (mouth, vulva, anus, cloaca) and gradually spread throughout ifs body . In cases of difficult diagnosis, therefore, it is recommended that rite n odule be sectioned at different points comprising caudal, cephalic and midd le body aspects, so as to reveal the Jew morphologic features that ale stil l recognizable and which may afford a correct diagnosis. The authors presen t examples of histologic sections in color plates in which the nematode was in an excellent state of preservation and others illustrating the full ran ge of regressive phenomena, from slight to total disintegration of the bodi ly structure. (C) 1999 Elsevier Science Inc.