Field Evaluation of Feasibility & Ease-of-Use of Novel Onchocerciasis Diagnostics - Ghana

Background: Onchocerciasis, causing severe itching, blindness, and economic hardship, is a target for elimination by the WHO. Accurate diagnostics are crucial for identifying areas of transmission and for stopping treatment. However, traditional diagnostics like skin-snipping and SD Ov16 ELISA tests have limitations, preventing their use as decision-making tools. This study evaluates the performance, feasibility, and ease of use of two new lateral flow assays (GADx Oncho test and DDTD multi-antigen test) for point-of-care (POC) and lab-based diagnosis, comparing them with existing SD Ov16 RDT and the skin snip PCR.
Methods: The study conducted head-to-head comparisons of the GADx and DDTD tests with the SD Ov16 RDT on whole blood in the field and dried blood spots in the lab. Participants 5 years and above were enrolled in the study. Field testing was implemented on whole blood collected from all participants in seven communities across different onchocerciasis-endemic regions in Ghana, and DBS samples were collected for laboratory testing. Skin snip samples were also collected from adults and tested in the laboratory using the O-150 qPCR. Blood samples were also tested for infections with Mansonella perstans using the qPCR, to assess any cross-reactivity with the tests. The sensitivity of the tests was assessed by comparing them with the SD and the skin-snip PCR data.
Results: Out of 1,700 enrolled participants, 1,696 participated in at least one of the tests. There was a substantial to near-perfect agreement between the results of the two tests, although the DDTD test identified more positives than the GADx test. However, the GADx test slightly outperformed the DDTD test in terms of sensitivity although the differences are not significant. For both RDTs, the tests run on eluted DBS in the lab provided the best results in terms of sensitivity. These tests meet the WHO DTAG TPP clinical sensitivity for mapping (>60%) but not for stopping (>89%). The skin snip qPCR returned only 26 positives, limiting the ability to undertake specificity assessments for the tests. The tests were easy to use in the field and in the lab.
Conclusions/Next Steps: Both GADx and DDTD tests demonstrated promise as onchocerciasis diagnostics for mapping purposes but require further refinement to meet the thresholds for MDA-stopping decisions. Further detailed analysis is ongoing, combining the data from Ghana with that from other countries to understand the relative performance of the GADx and DDTD RDTs with respect to the SD test. The samples collected during the study have been stored to enable the re-evaluation of future versions of the tests.