Insights Into Onchocerca volvulus Population Biology Through Multilocus Immunophenotyping

Abstract

We have developed a serologically based immunophenotyping approach to study Onchocerca volvulus (Ov) population diversity. Using genomic sequence data and polymerase chain reaction-based genotyping, we identified nonsynonymous single-nucleotide polymorphisms (SNPs) in the genes of 16 major immunogenic Ov proteins: Ov-CHI-1/Ov-CHI-2, Ov16, Ov-FAR-1, Ov-CPI-1, Ov-B20, Ov-ASP-1, Ov-TMY-1, OvSOD1, OvGST1, Ov-CAL-1, M3/M4, Ov-RAL-1, Ov-RAL-2, Ov-ALT-1, Ov-FBA-1, and Ov-B8. We assessed the immunoreactivity of onchocerciasis patient sera (n = 152) from the Americas, West Africa, Central Africa, and East Africa against peptides derived from 10 of these proteins containing SNPs. Statistically significant variation in immunoreactivity among the regions was seen in SNP-containing peptides derived from 8 of 10 proteins tested: OVOC1192(1-15), OVOC9988(28-42), OVOC9225(320-334), OVOC7453(22-36), OVOC11517(14-28), OVOC3177(283-297), OVOC7911(594-608), and OVOC12628(174-188). Our data show that differences in immunoreactivity to variant antigenic peptides may be used to characterize Ov populations, thereby elucidating features of Ov population biology previously inaccessible because of the limited availability of parasite material.

Keywords: Onchocerca volvulus; immunophenotype; immunoreactivity; population biology; single nucleotide polymorphism.

Figure 1.

Immunoreactivity against variant peptides significantly differs by region. A, Heatmap of semisupervised clustering of the normalized optical density (OD) values, with a color scale ranging from low (dark blue) to high (dark red). B–K, Scatterplot graphs of OD for each variant peptide, with geometric means indicated by the horizontal lines. The geographic regions are indicated on the x-axis; the OD values are indicated on the y-axis. The false discovery rate–adjusted P values from analysis of variance are listed on each graph. Abbreviations: Am, Americas; CA, Central Africa; EA, East Africa; WA, West Africa.

Figure 2.

Binary responses of immunoreactivity against variant peptides significantly differs by region. A, Binary responses for each peptide with immunoreactive (dark gray) and nonreactive (light gray) patients. B–K, Normalized proportions of binary responses for each variant peptide. Geographic regions are indicated on the x-axis, and the proportions of immunoreactive (black) and nonreactive (gray) patients are indicated on the y-axis. Abbreviations: Am, Americas; CA, Central Africa; EA, East Africa; WA, West Africa.