Performance evaluation of 3 serodiagnostic peptide epitopes and the derived multi-epitope peptide OvNMP-48 for detection of Onchocerca volvulus infection

Abstract

Current diagnostic tools to determine infection with the helminth parasite Onchocerca volvulus have limited performance characteristics. In previous studies, a proteome-wide screen was conducted to identify linear epitopes in this parasite’s proteome, resulting in the discovery of 1110 antigenic peptide fragments. Here, we investigated three of these peptides using peptide ELISA’s and evaluated their sensitivity and specificity. Epitope mapping was performed, and peptides were constructed that contained only the minimal epitope, flanked by a linker. Investigation of the performance of these minimal epitope peptides demonstrated that all three of them have a specificity (as defined by lack of response in non-helminth-infected individuals) of 100%, low cross-reactivity (5.6%, 5.6%, and 9.3%, respectively), but low sensitivity (36.9%, 46.5%, and 41.2%, respectively). Some cross-reactivity was observed in samples from individuals infected with soil-transmitted helminths or Brugia malayi . Combining these three minimal epitopes in a single peptide, called OvNMP-48, resulted in a performance that exceeded the sum of the individual epitopes, with a sensitivity of 76.0%, a specificity of 97.4%, and a cross-reactivity of 11.1%. Cross-reactivity was observed in some STH and Brugia malayi -infected individuals. This work opens the opportunity to start exploring how these novel linear epitope markers might become part of the O. volvulus diagnostic toolbox. Electronic supplementary material The online version of this article (10.1007/s00436-019-06345-3) contains supplementary material, which is available to authorized users.

Assessment of multiplex Onchocerca volvulus peptide ELISA in non-endemic tropical regions

“…Comparing the results of the multiplex ELISA with the previously published singleplex ELISA [12, 13, 17] showed a correlation between the spot intensities (multiplex assay) and absorbance (singleplex assay). The intensity measured in the multiplex assay rapidly increased with increasing antibody levels and started to saturate at a level that corresponds with an absorbance of 1 (Fig.…”

“…Regression lines were calculated using least squares fit. Spot intensity cut-offs are indicated by the horizontal dashed lines; absorbance cut-offs are indicated by the vertical dashed lines [12, 13]…”

“…The 3-peptide positives algorithm would label > 40% seropositive for O. volvulus in Kenya, a result that is in strong disagreement with the epidemiology of onchocerciasis. It was concluded that the three peptides bearing linear O. volvulus epitopes are recognized by antibodies induced by either/or O. volvulus and yet another immunogen, but not STH, S. mansoni , W. bancrofti , B. malayi , HIV, HCV, dengue, and possibly also not by the malaria parasite [12, 13, 18]. The majority of the endemic control samples from Ghana were found to be positive for peptides OvMP-1, OvMP-23 and/or OvNMP-48, with 83.3% of them positive for all three peptides.…”

“…The observed cross-reactivity on the O. volvulus derived peptides opens an additional discussion on the quality check of the biobanks used for biomarker discovery activities. Since discovery of these peptides was performed on samples from Cameroon [14] and confirmation of their reactivity was done on samples from Ghana, Indonesia, Sri Lanka [12, 13] and Kenya, we came to the conclusion that, despite the careful selection of samples, we knew little or nothing of other filaria past or present co-infections. Therefore, validation of candidate biomarkers should be performed on extremely well-characterized samples for multiple infections.…”

“…Plasma samples from O. volvulus infected individuals, healthy controls, W. bancrofti- infected individuals, individuals with B. malayi infection and individuals infected with soil-transmitted helminths (STH) and/or Schistosoma mansoni have been described before [12, 13, 17]. An overview, including Ov16 IgG4 information is provided in Table 1.…”