Microfilariae have been evaluated as
antigen for the indirect immunofluorescent test in the diagnosis of
filariasis. Sonicated, unlike whole, microfilariae present no problems in handling on a slide. The cytoplasmic
antigen that is exposed by sonication, unlike the sheath or cuticular
antigen, reacts with
filariasis sera irrespective of whether or not there is a detectable microfilaraemia. The cytoplasmic
antigen of microfilariae of various species was marginally superior to Dirofilaria adult worm as
antigen for diagnostic immunofluorescence in respect of both sensitivity and specificity. The microfilariae extruded from the uterus of an adult D. immitis were a useful source. But the best results were obtained with the sonicated microfilariae of Brugia pahangi, with which it was possible to utilize both cytoplasmic and sheath
antigens simultaneously, giving a positivity rate of 95% for
filariasis infecions as a group. This test is thought to be the best available at present for the sero-diagnosis of
filariasis, in spite of some lack of specificity. For individual filarial
infections a homologous microfilarial
antigen is probably the deal.