An Antibody Biomarker Associated with Onchocerca volvulus Microfilariae Identified by Proteomic Analysis of Parasite Tissues Isolated from Paraffin Embedded O. volvulus Nodules by Laser Capture Microdissection.

Onchocerciasis (river blindness), a neglected tropical disease caused by the filarial nematode Onchocerca volvulus, impacts millions of people in sub-Saharan Africa. The WHO coordinates global efforts to eliminate onchocerciasis and has prioritized development of improved diagnostic tests to aid these efforts. To find new microfilarial-associated diagnostic targets to help identify active infections, we used laser capture microdissection to isolate embryonic stages from histologic sections of O. volvulus worms in subcutaneous nodules excised from onchocerciasis patients. Proteomic analysis identified 2,512 O. volvulus proteins in those tissues, including 264 found only in the microfilariae (Mf). From this pool of diagnostic candidates, we selected OVOC12404, a putative cuticular collagen, for further study because of its abundance and lack of close homologues in other filarial species. Immunolocalization detected this antigen on the surface of coiled, stretched, and tissue Mf. IgG antibodies to OVOC12404 were detected by ELISA in plasma from 124 of 162 (76.5%) people with O. volvulus Mf in their skin snips. ELISA specificity was 98% based on 42 samples from lymphatic filariasis patients from areas without co-endemic onchocerciasis. In contrast to antibodies to Ov16, a currently used diagnostic target, antibodies to OVOC12404 declined significantly after treatments that cleared O. volvulus Mf from the skin. This study showed that proteomic analysis of parasite tissues recovered from histological sections can be used to identify stage-specific filarial diagnostic targets. Further studies are needed to assess the potential value of an OVOC12404 antibody test as an additional diagnostic tool to support the onchocerciasis elimination efforts.