A Four-Antigen Mixture for Rapid Assessment of Onchocerca volvulus Infection

Abstract

Onchocerciasis, an infection caused by the filarial nematode Onchocerca volvulus, is a major public health concern. Given the debilitating symptoms associated with onchocerciasis and concerns about recrudescence in areas of previous onchocerciasis control, more efficient tools are needed for diagnosis and monitoring of control measures. We investigated whether luciferase immunoprecipitation systems (LIPS) may be used as a more rapid, specific, and standardized diagnostic assay for Onchocerca volvulus infection. Four recombinantly produced Onchocerca volvulus antigens (Ov-FAR-1, Ov-API-1, Ov-MSA-1 and Ov-CPI-1) were tested by LIPS on a large cohort of blinded sera comprised of both uninfected controls and patients with a proven parasitic infection including Onchocerca volvulus (Ov), Wuchereria bancrofti (Wb), Loa loa (Ll), Strongyloides stercoralis (Ss), and with other potentially cross-reactive infections. In addition to testing all four Ov antigens separately, a mixture that tested all four antigens simultaneously was evaluated in the standard 2-hour incubation format as well as in a 15-minute rapid LIPS format. Antibody responses to the four different Ov antigens allowed for unequivocal differentiation between Ov-infected and uninfected control sera with 100% sensitivity and 100% specificity. Analysis of the antibody titers to each of these four antigens in individual Ov-infected sera revealed that they were markedly different and did not correlate (r_S = –0.11 to 0.58; P = 0.001 to 0.89) to each other. Compared to Ov-infected sera, patients infected with Wb, Ll, Ss, and other conditions had markedly lower geometric mean antibody titers to each of the Ov 4 antigens (POv antigens simultaneously in the standard format or a quick 15-minute format (QLIPS) showed 100% sensitivity and 100% specificity in distinguishing the Ov-infected sera from the uninfected control sera. Finally, the QLIPS format had the best performance with 100% sensitivity and specificity values of 76%, 84% and 93% for distinguishing Ov from Wb, Ll and Ss-infected sera. The multi-antigen LIPS assay can be used as a rapid, high throughput, and specific tool to not only to diagnose individual Ov infections but also as a sensitive and potentially point-of-care method for early detection of recrudescent infections in areas under control and for mapping new areas of transmission of Ov infection. Caused by the filarial parasite Onchocerca volvulus, onchocerciasis is a neglected tropical disease associated with blindness and severe dermatitis. Available diagnostic methods are either invasive, require hours or days to perform, and/or need sophisticated equipment to be conducted. Thus, there is an urgent need for simple and rapid technologies for the specific diagnosis of Onchocerca volvulus infection. Here we investigated whether luciferase immunoprecipitation systems (LIPS) can produce a more rapid and specific test for diagnosis of O. volvulus infection. Using modified versions of previously identified Onchocerca-specific antigens, LIPS tests detected antibodies to all four O. volvulus antigens and easily distinguished the O. volvulus-infected samples from uninfected samples. We also tested these four different antigens in a simpler format as a combined mixture and distinguished 100% of the confirmed cases from the uninfected controls. A rapid 15-minute version of this mixture test (QLIPS) also allowed distinction of 100% of the cases from those uninfected and performed even better in identifying Onchocerca from other cross-reactive parasitic infections. This study suggests that this rapid LIPS test (QLIPS) has the potential to be used in point-of-care detection of onchocerciasis and thereby may provide a new tool for diagnosis and the monitoring of transmission control measures.